the star formation newsletter · three-volume ”amateur telescope making” (atm) series by...

THE STAR FORMATION NEWSLETTERAn electronic publication dedicated to early stellar/planetary evolution and molecular clouds

No. 242 — 10 February 2013 Editor: Bo Reipurth ([email protected])

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The Star Formation Newsletter

Editor: Bo [email protected]

Technical Editor: Eli [email protected]

Technical Assistant: Hsi-Wei [email protected]

Editorial Board

Joao AlvesAlan Boss

Jerome BouvierLee Hartmann

Thomas HenningPaul Ho

Jes JorgensenCharles J. Lada

Thijs KouwenhovenMichael R. MeyerRalph Pudritz

Luis Felipe RodrıguezEwine van Dishoeck

Hans Zinnecker

The Star Formation Newsletter is a vehicle forfast distribution of information of interest for as-tronomers working on star and planet formationand molecular clouds. You can submit materialfor the following sections: Abstracts of recently

accepted papers (only for papers sent to refereedjournals), Abstracts of recently accepted major re-

views (not standard conference contributions), Dis-

sertation Abstracts (presenting abstracts of newPh.D dissertations), Meetings (announcing meet-ings broadly of interest to the star and planet for-mation and early solar system community), New

Jobs (advertising jobs specifically aimed towardspersons within the areas of the Newsletter), andShort Announcements (where you can inform or re-quest information from the community). Addition-ally, the Newsletter brings short overview articleson objects of special interest, physical processes ortheoretical results, the early solar system, as wellas occasional interviews.

Newsletter Archivewww.ifa.hawaii.edu/users/reipurth/newsletter.htm

List of Contents

Interview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

My Favorite Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Abstracts of Newly Accepted Papers . . . . . . . . . . 14

Abstracts of Newly Accepted Major Reviews . 49

Dissertation Abstracts . . . . . . . . . . . . . . . . . . . . . . . . 50

Meeting Announcements . . . . . . . . . . . . . . . . . . . . . . 53

Other Meetings of Possible Interest . . . . . . . . . . . 56

Short Announcements . . . . . . . . . . . . . . . . . . . . . . . . 58

Cover Picture

This image shows the Horsehead Nebula (Barnard33) in the lower right corner, together with the re-flection nebula NGC 2023 (to the upper left) illu-minated by the B1.5 star HD 37903. The imagewas taken with ESO’s new survey telescope VISTAat the Paranal Observatory through J, H, and Ksfilters. North is up and east is left. A bright youngstar, B33-1, is located at the northwestern corner ofthe Horsehead, together with a fainter young starjust south of it, also at the edge of the ionizationfront.

Image courtesy ESO/J. Emerson/VISTA. Acknowl-edgment: Cambridge Astronomical Survey Unit.

Submitting your abstracts

Latex macros for submitting abstractsand dissertation abstracts (by e-mail [email protected]) are appended toeach Call for Abstracts. You can alsosubmit via the Newsletter web inter-face at http://www2.ifa.hawaii.edu/star-formation/index.cfm

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John Ballyin conversation with Bo Reipurth

Q: You were born in Hungary?

A: I was born in Szombathely, Hungary as Janos IstvanCsaba Pogacsas. My mother, Livia Bally, and I left hun-gary in 1957 after the Soviet invasion, spent about sixmonths in Austria and one and a half years in Italy whilewaiting for quotas to open-up to enter the United States.My great uncle Laszlo Hudec (see Wikipedia) and his wifeGisella who lived in Berkeley sponsored our entry. Laszlosuggested that in the States, instead of Pogacsas, I usemy mother’s maiden name, Bally. Thus, I became JohnBally. Unfortunately, Laszlo died a few months before wearrived, but Gisella took us in. I started school in Berke-ley without knowing any English, so my teachers put mein the back of the classroom to work arithmetic problems.

Q: How did you become interested in astronomy?

A: Gisella gave me a small telescope, a 2.5” reflector, alongwith a small book, ”Stars; A Golden Nature Guide”. Thetelescope spent months in a closet. One night, I noticedan asterism I recognized from that book. I rememberedthe telescope, assembled it, and found the Pleiades. It wasa thrill to recognize something in the sky that I had onlyseen in pictures. On another evening I saw a spectacularbolide breaking up overhead. Thus, I looked for booksabout the sky in our junior high library and found thethree-volume ”Amateur Telescope Making” (ATM) seriesby Scientific American. At age 12, I convinced my parentsto buy me a mirror-making kit and I ground and polisheda 6” mirror in our basement bathroom. But, I had noidea how to get it aluminized. Following instructions inthe ATM books, I procured the chemicals to silver glass. Iobtained a functional coating and built a primitive equa-torial mount and tube, and started observing.

Q: Did you get further involved in amateur astronomy?

A: Yes, this became my passion. I ground more mirrorsand built telescopes. I learned about Chabot Observa-tory in Oakland which had 8” and 20” refracting tele-scopes and hosted the Eastbay Astronomical Society. Inmy early teens, I met John Dobson who hauled a 24”telescope to Mt. Diablo. I joined his ‘San Francisco Side-walk Astronomers’ at star parties on Freemont Peak (nearMonterey) and Glacier Point in Yosemite and saw stun-ning views of the planets, clusters, nebulae, and galaxies.I was hooked on the beauty of the sky.

I read an article in the local paper about George Herbig.The article described his work on star formation at LickObservatory, and what I later learned were his studies ofthe Herbig-Haro objects and T Tauri stars in Orion. Thiscontributed to my interest in astronomy.

I loved to play with optics. I discovered the benefits of un-obstructed optical systems. One design dubbed the ”Yolo”(after the Central Valley county) used a pair of tilted long-focus concave spheres and a warping harness to removeastigmatism. It delivered the best high contrast images Ihad ever seen. I experimented with my own tilted mir-ror telescopes and won a science fair in 10th grade. Myoptics experience was noticed by my high-school teachers.In 12th grade at J.F. Kennedy high-school in Richmond, Igave lectures on optics and telescopes to my class-mates.I was given keys to Chabot where I took many lunar andplanetary photos and long, hand-guided exposures.

In August 1968, after graduating from high school, ata star-party at an amateur astronomy conference in LasCruces, New Mexico, I was searching for the Ring Nebulawith a 10” telescope which had no finder. Sweeping thesky in Lyra, I chanced upon an unexpected fuzzy object ina patch of sky I knew well. Comet Bally-Clayton made thepress and prompted me to study astronomy at Berkeley.

I earned my way through college by living in the co-opsfor room and board and assisting with planetarium shows,school programs, and public observing nights at the ChabotObservatory. I found an old diffraction grating in the base-ment with an inscription, ”Ruled on Roland’s machine,1882”. I built a spectrograph to house it, took spectra ofstars, the brightest nebulae, and showed the Solar spec-trum to visiting students and the public. As a result ofmany nights at Chabot, the turbulent times in Berkeley(these were the days of the Vietnam war protests), andspending too much time with amateur astronomy, my un-dergraduate grades suffered. My advisors said I wouldnever become a scientist.

Q: How did you get into graduate school after such a non-

stellar undergraduate career?

A: After Berkeley, I became a ski-bum at Lake Tahoe.In the evenings I read Richard Feynmann’s ”Lectures inPhysics” and fell in love with the subject. I spent the fol-

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lowing year at Cal State Hayward ‘brushing-up’ on basicphysics and getting A’s. In Fall 1973, I toured the StanfordLinear Accelerator and SPEAR, the electron-positron col-lider, which triggered my interest in high-energy physics. Iapplied to graduate schools on the East coast of the UnitedStates to make a clean start in physics or astronomy.

I entered graduate school in Amherst at the University ofMassachusetts in Fall 1974 spending my first year in MikeKraisler’s high energy physics group building and calibrat-ing scintillator plastic and Cerenkov detectors. Duringthe following summer at Brookhaven, I tested componentsand mapped detector magnetic fields for an experiment tomeasure the form factors of the Λ particle (similar to theneutron but with a strange quark substituted for one ofthe down quarks). But, I decided that a large group withhundreds of others was not for me.

Next, I worked with Ted Harrison on a cosmology problemwhich resulted in my first ApJ paper. Then, I workedwith Gene Tadamaru on pulsars. Could the radiation forceof a rapidly rotating, offset, tilted dipolar magnetic fieldproduce high-velocity pulsar kicks? After months of workon multipole expansions, I realized this was not for me.

Nick Scoville ”rescued” me from theory, invited me on anobserving run on the Kitt Peak 50” to search for Brackett-γ emission from the Galactic center. In addition to ourGalactic center paper, the run produced the first (or atleast early) measurement of Brackett-α and γ from themicro-quasar SS433. He involved me in commissioningthe 14-meter mm-wave FCRAO radio telescope. I workedon gaussian optics, pointing corrections, and learned themethods of mm-observations. My thesis on the interac-tion of HII regions with molecular clouds became the firstPhD (in 1980) based on the 14-m dish. I obtained COobservations of the North America and Pelican Nebulae,S87, S106, and several other HII regions. I continued IR-observations from Kitt Peak, including a memorable earlyspectroscopic study of 2 µm H2 emission from the recentlydiscovered BN/KL outflow in Orion using the 36” Westauxiliary telescope on the McMath Solar facility and usedthe 50” to search for H2 in outflows from star-forming re-gions such as NGC 2071 and Cepheus A.

Q: What did you do after graduate school?

A: As a result of my instrumental and mm-wave expe-rience, Bill Langer, who served on my thesis committee,suggested I contact Bob Wilson at AT&T Bell Laborato-ries about a postdoc in the Radio Physics Research De-partment in Holmdel, New Jersey. I started at AT&T in1980. My first project was with Tony Stark on a 21 cm HIsurvey using the horn antenna that discovered the CMB.The offset parabolic horn had an exceptionally clean, wellcharacterized beam for measurement of the true minimumcolumn density of HI in the Lockman Hole. My second

project was to search infrared sources in star forming re-gions for outflows with the 7-meter offset Cassegrain an-tenna. I met my wife Kim, an engineer, at Bell Labs in1981. Two children, Trina and Lex, followed.

I spent the next eleven years in the remarkable environ-ment of Bell Labs. We were judged on what we wereaccomplishing rather than on proposals. I had funding tosupport continued infrared observations on Kitt Peak andradio-follow-ups of outflow detections at the VLA. The COoutflow survey was published with Charlie Lada in 1983and my postdoc was converted into a permanent position.With dedicated use of the 7-meter I fully mapped cloudssuch as Perseus, Orion, and the Central Molecular Zone,obtaining CO, 13CO, and CS J=2-1 maps with 104 to over105 spectra, data sets of unprecedented size at the time.

The Crawford Hill astronomy group consisted of Bob Wil-son, Rich Linke, Tony Stark, and me, with occasionalparticipation by Arno Penzias and visitors such as BillLanger. Full utilization of the 7-meter required develop-ment of automated data acquisition, remote monitoring,and antenna control through phone-lines. We ran observa-tions from home and around the clock. We hosted dozensof students and researchers from nearby universities andinternational institutions.

I worked on free-space optics for communications appli-cations and characterization of atmospheric transmissionat wavelengths where commercial laser diodes and com-munications hardware were available. I needed a high-resolution spectrometer. A verbal request for $200,000 fol-lowed by a two paragraph description of the project got methe purchase order for the instrument the next day. BellLabs was a unique and special place! Management real-ized that by investing in enough basic research, discoverieswould emerge to provide a bright future for the business.We were encouraged to experiment. We made lithograph-ically generated fresnel zone plates, orthogonally-orientedbent cylindrical parabolic surfaces, and vacuum-formedmylar membrane mirrors as inexpensive laser flux concen-trators for communications applications, and possibly asmm-wave optics. We built the first working SIS receiversusing lead-lead oxide-lead Josephson junctions.

In 1984, the US Justice Department ordered the break-upof the Bell System monopoly on the telecommunicationsmarket. Support for fundamental research at Bell Labssoon came to an end. By 1992, most of the dozen as-tronomers had left the Labs.

Q: How did you become involved with Antarctica?

A: Around 1985, Mark Dragovan was hired as a post-doc. He proposed to take small antennae to South Polein an early attempt to measure the CMB-anisotropy. TheCrawford Hill group started discussions with NSF PolarPrograms to explore the potential of South Pole for astron-

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omy. Tony Stark won funding to build the Antarctic Sub-mm Telescope and Remote Observatory (AST/RO). In thelate 1980s, we were invited by Al Harper (Yerkes Obser-vatory) to participate in a proposal to the NSF to fund the”Center for Astrophysical Research in Antarctica” (CARA),an 11-year program to do astronomy at South Pole. CARAwas funded and AST/RO was installed at South Pole Sta-tion.

In December 1991, I left Bell Labs for good, taking the‘long-route’ to Boulder via South Pole. I borrowed a 230GHz tipping radiometer from NRAO and installed it atPole and started collecting two years of 1.3 mm transmis-sion and ‘sky-noise’ measurements which confirmed theexcellent sub-mm conditions. I borrowed a 6” refractorfor visual-wavelength seeing measurements. The seeingduring the austral night turned out to be awful with 5”PSFs or worse due to the 20 C deep thermal inversionwhich formed about 500 meters above the ice. Micro-thermal sensors on balloons demonstrated that turbulencewas generated in the ground layer. But the integratedseeing above the inversion layer was likely to be excellent.During the early 1990s, I was in charge of site characteri-zation for CARA. We used a Hartmann-Differential ImageMotion Monitor (H-DIMM) to observe stars with a multi-aperture mask. The camera was slightly de-focused sothat the sub-apertures were diffraction limited but well-separated on the CCD. Image motion correlation analysison suitable double stars enabled the profiling of the verti-cal distribution of turbulence.

Q: How did you get involved with HST and the proplyds

and giant Herbig-Haro outflows?

A: In 1986, at one of the star formation workshops inSanta Cruz, Hans Zinnecker and I were wondering whata T Tauri star might look like when immersed in an HIIregion and irradiated by nearby O stars? Could the result-ing ionization fronts be observed spectroscopically? WhenI arrived in Boulder, I wrote the words, ‘PIGS, DEERS,and FOXES’ on my board, these being acronyms for ’Par-tially Ionized Globules’, ‘Deeply Embedded Energetic Ra-dio Sources’, and ‘Fluctuating Optical and X-ray EnergySources’ that were coined in various papers on the OrionNebula. David Devine (my first graduate student in Boul-der) and I wrote a proposal to search for the externallyionized T-Tauri stars in Orion and got time on the KPNO0.9-m and 2.1-m telescopes to search for the expected sig-natures predicted by Ralph Sutherland with the Mappingscode. Before our run, we heard about Bob O’Dell’s discov-ery of proplyds on HST images. We were one of the firstto use the 2k by 2k CCD T2KA with an unprecedented23’ FOV and decided to see what it could do on HH 34.As the first narrow-band images appeared, we saw thatHH 34 was merely the inner portion of a 3 pc-long outflowcontaining other previously known HH objects such as HH

33/40. I recall e-mailing you about this result and you in-vited me to visit the NTT in January 1994 to explore thisfurther. On that run we realized that many classic HHflows were an order-of-magnitude larger than previouslythought. KPNO 4-m spectra provided confirmation of the‘giant HH flow’ hypothesis.

Following the 1994 repair mission, we started using HSTto observe irradiated T Tauri stars - the proplyds - lead-ing to a decade-long study of the environment of planetformation in HII regions, the discovery of externally irra-diated jets, and visual wavelength narrow-band surveys ofmost of the nearby star forming clouds at NOAO. Withinthe last fifteen years, we found hundreds of new HH ob-jects, dozens of giant flows, and have come to appreciatethe role of outflows as the lowest rung of the ‘feedbackladder’ in star formation that self-regulates the process.HST, and the Mosaic CCDs on the CTIO and KPNO fourmeter telescopes, were essential for these discoveries.

Q: How did your career evolve in the last decade?

A: In the mid-1990s I joined the CU Boulder Astrobiol-ogy Center as the ‘astrophysicist’ where I worked on theemerging view that most stars and their planetary systemsform in dense but short-lived transient clusters where theyare bathed in UV radiation, shocks, and other harsh en-vironmental factors such as nearby supernovae. Abouteight years ago I became involved with Bolocam on theCSO, proposing to conduct a dust-continuum survey ofthe Northern Galactic plane at 1.1 mm. The BolocamGalactic Plane Survey (BGPS) is just now being releasedin its final form. I participate in the Hershel Space Obser-vatory Hi-GAL Galactic plane survey. My interests havereturned to the Central Molecular Zone and the nature ofmassive star and star cluster formation. I see outflows andHerbig-Haro objects in the broader context of the feed-back ladder and as a stage in the self-regulation of starformation. I’ve re-kindled my early interests in cosmologyand fundamental physics, enjoy teaching classes in thesesubjects, and am exploring and learning the literature.

Q: Do you still ski?

A: Absolutely! We built a home in Breckenridge, Coloradoat an elevation of 10,800 feet that looks directly at the skiarea. Kim is retired, enjoys the musical environment ofBreckenridge, and loves to play her 7.5 foot grand piano.We occasionally give concerts in our living room. We builta small observatory over the garage where I keep threetelescopes, currently a 17.5” being the largest. I have a24” mirror ready to mount once I have a weldment made.My CCDs are used to calibrate large-telescope data andto take stunning pictures. I still marvel at the beauty ofthe sky and never tire of seeing the clusters, nebulae, andgalaxies familiar since childhood. We are both returningto our childhood passions.

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My Favorite Object

The Horsehead’s Maneby Jerome Pety

Located in the Orion constellation, the Horsehead nebulais one of the most famous and easily-recognizable objectsin the sky. For instance, its light-bathed silhouette wasselected by internet voters as the target for the 11th an-niversary of the Hubble Space Telescope (See the Hub-ble Heritage site for details). The nebula, also known asBarnard 33, was first discovered by Williamina Flemingin the late 1800s on a photographic plate taken at theHarvard College Observatory. At visible wavelengths, itappears as a 5-arcminute dark patch against the brightHα emission from the HII region IC 434. At mid-infraredand radio wavelengths, on the other hand, the nebula isbright due to dust and molecular emission.

The closest radiatively sculpted pillar to Earth:Named for its optical appearance, the shape of the neb-ula at radio wavelengths is indeed more reminiscent of aseahorse (cf., the middle left image in Fig. 1)! A curvedrim including the nose, ridge and mane of the horse is lo-cated at the western end of the nebula (i.e., the top ofthe head). This ridge is connected to the eastern L1630molecular cloud by a filament, the horse’s neck. While op-tically thick tracers like the 12CO lines show a low densityhalo surrounding the neck, optically thin tracers like thedust emission (from 1.2mm to 350µm) or C18O J=2–1emission reveal the presence of two dense condensations:the first one associated with the western ridge, called B33-MM1, and the second one in the middle of the neck, calledB33-MM2.

Two massive stars are located at the same projected dis-tance of the Horsehead (0.5◦), the O9.6Ib star ζOri northof the nebula and the O9.5V star σOri west of the neb-ula. However, Hipparcos estimates of their distance (Per-ryman et al. 1997) indicate that ζOri (250± 50 pc) is lo-cated further away from the Horsehead nebula than σOri

(352±113 pc). Using the 12CO J=4–3/J=2–1 ratio, whichis an excellent tracer of the direction of the incoming farUV photons, Philipp et al. (2006) determined that thefar UV illumination primarily comes from σOri. This in-cident radiation field shaped the molecular cloud into thefamous Horsehead.

Reipurth & Bouchet (1984) were the first to suggest thatthe Horsehead nebula formed through the photoevapora-tion of low density material around the neck which wasprotected by the shadow of denser material in the ridge.Following this pioneer work, Pound et al. (2003) cast theHorsehead nebula in the category of the pillars like thewell-known examples in the Eagle nebula. The typical sizeand velocity gradients thus imply a formation timescale of∼ 0.5Myr and a timescale of destruction through pho-toablation of ∼ 5Myr. Hily-Blant et al. (2005) showedthrough careful measurement of velocity gradients in theC18O J=2–1 emission that the gas is rotating around theneck axis. The velocity gradients perpendicular to theneck axis are reasonably constant around an average valueof 1.5 km s−1 pc−1 (implying a rotation period of 4Myr)except at the position of the dense condensation B33-MM2, where the transverse velocity gradients experiencea sharp increase up to 4 km s−1 pc−1. The overall shape ofthe neck is thus assumed to be cylindrical with a fairly con-stant projected diameter of about 0.15–0.30 pc. Since thisstudy, Gahm et al. (2006) have confirmed that rotation ofgas around pillar major axes is a common phenomenon.At 400 pc from Earth, the Horsehead nebula is thus theclosest known example of pillar. This recently triggereda numerical study of its formation by Tremblin et al. (inprep.).

Ward-Thompson et al. (2006) derived the main character-istics of the two condensations of the Horsehead nebula.Assuming a temperature of 15K, the mass of the easterncondensation (B33-MM2) is ∼ 4M⊙ in a region of dimen-sion 0.15 × 0.07 pc. This yields an average H2 density of105 cm−3 while the peak density is 2×106 cm−3. Virial es-timates imply that this dense core is in approximate gravi-tational equilibrium. The size of the western condensation(B33-MM1) is 0.13× 0.31 pc and its mass is ∼ 2M⊙ (as-suming a temperature of 30K). This yields an average H2

density of 104 cm−3 while the peak density is 6×105 cm−3.Its virial balance is however largely dominated by the ion-izing field. Both condensations are potential progenitors ofthe next generation of star formation and may thus giveclues about the differences between triggered and spon-taneous star formation. Indeed, Reipurth & Bouchet etal. (1984) made an early census of star formation in theHorsehead nebula. In a more detailed study, Bowler etal. (2009) found five candidate young stars, plus a classII young stellar object, and two protostars located just atthe north-western illuminated edge of B33-MM1.

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Figure 1: 3D-view (position, position, frequency) of the Horsehead. The upper and lower panels display the spectraof the 3mm band at a spectral resolution of 49 kHz for two different positions in the Horsehead Nebula, obtainedat the IRAM-30m with the combination of EMIR receivers and FTS backends in about 60 hours. Each spectra hasabout 740 000 channels, i.e., as much information as in an image of 860 × 860 pixels! The median noise is about8mK. The survey positions correspond to two different environments located inside the white square on the C18OJ=2–1 integrated emission map (wide, left image obtained with the IRAM-30m/HERA multi-beam): 1) the photo-dissociation region (PDR) marked by the green cross on the CCH emission map (middle, top image, IRAM-PdBI),and 2) the dense core marked by the blue cross on the DCO+ emission map (middle, bottom image, IRAM-PdBI).The middle right panels display two lines zoomed from the surveys.

A prototypical, low illumination Photon-DominatedRegion: High density gas and far-UV stellar light inter-act at the illuminated edge of the western condensation,forming a Photon-Dominated Region (PDR) where thephysics and chemistry is driven by the far-UV radiation.PDRs play an important role in astrophysics as they arefound everywhere in the interstellar medium, e.g. in dif-fuse gas, star forming regions, protoplanetary disks, andcircumstellar envelopes around evolved stars. Moreover,PDRs dominate the IR and sub-mm spectra in externalgalaxies. Understanding PDRs thus sheds light on theseobjects. Therefore, numerous models have been developedto study the different physical and chemical processes in-

volved in PDRs since the early 1970’s (Rollig et al. 2007).This requires good modeling of many microscopic pro-cesses (UV radiative transfer, heating, cooling, turbulentmixing, gas phase and grain surface chemistry) with verydifferent timescales. It also relies on many different mi-crophysical parameters (e.g., chemical rates, adsorptionand desorption coefficients, etc...) calculated/measuredby several theoretical and experimental groups. However,the difficulty of this last effort implies that only a few re-actions (among the thousands used in chemical networks)can be thoroughly studied.

In view of the intrinsic complexity of building reliablechemical networks and models, there is an obvious need

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of well-constrained observations that can serve as basicreferences. PDRs are particularly well suited to serve asreferences because they make the link between diffuse anddark clouds, thus enabling to probe a large variety of phys-ical and chemical processes. In this context, the Horseheadis particularly interesting because it has the most simplegeometry we can hope to find in the interstellar medium,i.e., edge-on.

Indeed, the Horsehead edge presents one of the thinnestinfrared filaments (width < 10′′ or 0.02 pc) detected inour Galaxy by ISOCAM. The most straightforward ex-planation given by Abergel et al. (2003) is that the densematerial features a flat interface, viewed edge-on and illu-minated in the plane of the sky by σOri, as other geome-tries would broaden the filament. The 2.12µm H2 fluores-cent emission observed by Habart et al. (2005) with theSOFI instrument on the NTT telescope is even sharper(width: 5′′), implying the inclination of the PDR on theplane-of-sky to be less than 5◦. Abergel et al. (2003)deduced from the distance between σOri and the PDR(3.5 pc) that the intensity of the incident far UV radia-tion field is χ ≃ 60 times the mean interstellar radiationfield (Draine 1978). This is relatively low compared toother well-studied PDRs (e.g., the Orion Bar, NGC 7023,Mon R2,...) where χ ≃ 104 − 105. While this implies thatthe Horsehead PDR is a fainter source, its properties arecloser to a large fraction of the interstellar volume.

Habart et al. (2005) constrained the gas density structureperpendicular to the PDR front through a careful mod-eling of the H2, CO, and PAH emission. The observedspatial stratification, the absolute intensities, and the in-tensity ratios of the different tracers imply that the den-sity must follow a steep gradient at the cloud edge, risingto nH = 105 cm−3 in less than 10′′, at a constant ther-mal pressure (4× 106 Kcm−3) more than 100 times largerthan the mean interstellar pressure. Gerin et al. (2009)detected bright lines (1.5K) of the HCO radical at about15′′ from the PDR edge. At this position, HCO is as abun-dant as HCO+. This implies that the visual extinction isstill moderate (AV ∼ 1.5), the gas is warm Tkin ∼ 60K,while already relatively dense nH ∼ 6 × 104 cm−3. Wethus proposed that HCO is a good surface tracer of densefar-UV illuminated molecular gas.

Pety et al. (2007) detected very bright DCO+ lines (4K)less than 35′′ away from the peak of HCO emission. Thisconfirms that a UV-shielded (AV ∼ 10), cold (T = 10 −

20K), and dense (nH ≥ 2 × 105 cm−3) gas exists justbehind the PDR. The deuteration fraction of this sim-ple molecule is 2% in this dense core. Guzman et al.(2011) also detected deuterated formaldehyde (HDCO andD2CO) in the core with a high deuteration fraction([D2CO]/[H2CO] = 4%). An important consequence isthat it is relatively easy to disentangle the UV-illuminated

gas from the UV-shielded layers of the nebula with cur-rent instruments. We thus subsequently used in all ourstudies the HCO and DCO+ peak of emission as lines ofsight typical of the PDR and the dense core, respectively.

Using observations of DCO+, HCO+, and HOC+, Goicoecheaet al. (2009) showed that the electron abundance also fol-lows a steep gradient, with a scale length of ∼ 0.05 pc (or∼ 25′′), from [e−] = ne−/nH ≃ 10−4 in the PDR to a fewtimes 10−9 in the dense core. We showed that the gas-phase metal abundance, the cosmic-ray ionization rate,and the presence of PAHs and/or small grains play an im-portant role in the charge balance. This implies that it isdifficult to infer the value of any of them without informa-tion on others.

Complex organic molecules in a harsh UV-irradiatedenvironment, top-down chemistry, and other chem-ical surprises: From the chemical viewpoint, several im-portant results were also obtained. First, the detection ofHF in different sources by Herschel shed light on the flu-orine chemistry. In this context, Guzman et al. (2012a)made the second ever detection of CF+ towards the Horse-head PDR. The edge-on geometry implies quite narrowlinewidths (0.6−0.8 km s−1), which enabled us to constrainthe hyperfine structure of CF+ (Guzman et al. 2012b).The simple chemistry of CF+ implies that CF+ shouldfollow C+. We thus proposed that CF+, which is observ-able from the ground, could be used as a proxy of C+,an important coolant of the interstellar medium. Second,sulfur is an abundant element, which remains undepletedin diffuse interstellar gas and HII regions. But, it was his-torically assumed to deplete on grains in higher densitymolecular clouds by factors as large as ∼ 103 to accountfor the observed amount of CS. However, Goicoechea etal. (2006) showed for the first time that CS and HCS+

abundances can be reproduced by an almost undepletedsulfur abundance. This followed new laboratory measuresof the reaction rates and branching ratios of the electronicrecombination of HCS+ and OCS+ by Montaigne et al.(2005).

Teyssier et al. (2004) and Pety et al. (2005) showedthat small hydrocarbons, like CCH, c− C3H2 and C4Hare ubiquitous in these regions, with abundances almostas high as in dark, well shielded clouds. This was a sur-prise because they are expected to be destroyed by thestrong UV radiation present in these regions. They pro-posed that the incident radiation field can fragment PAHsinto these small hydrocarbons. Other possibilities are avariation of the cosmic ray ionization rate with the PDRdepth (Rimmer et al. 2012), and/or the transport of thesmall hydrocarbons formed deeper inside the cloud intothe UV-illuminated part by turbulent mixing (Lesaffreet al. 2007; Gerin et al. 2007). Indeed, Compiegne etal. (2007) have detected neutral PAHs in the ionised gas

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ahead of the Horsehead’s mane. The presence of PAHs canbe explained by 1) the continuous production of “fresh”matter through photo-evaporation of the Horsehead, and2) the long survival time of these PAHs in the HII region.Compiegne et al. (2008) also showed that the ratio ofPAHs to very small grains is 2.4 times larger in standarddiffuse gas than in the Horsehead PDR, suggesting thatthe dust properties evolve with the gas density when thegas crosses the UV-illuminated edge of PDRs. Recently,Pety et al. (2012) detected a consistent set of 6 unknownlines, which they tentatively1 attribute to C3H

+, an im-portant precursor of the other small hydrocarbons in thegas-phase. The derived abundance confirms the need fora new chemical route to form the small hydrocarbons inUV-illuminated regions, e.g., the photo-erosion of PAHs.All these studies are the first clear examples of the needof a top-down chemistry, i.e. from complex to simplemolecules, in addition to the usual bottom-up chemistry,in order to understand the organic inventory in space.

Finally, Guzman et al. (2011) and Gratier et al. (2013)found large amounts of complex molecules, like H2CO orCH3CN, in the Horsehead PDR. The effect is even moredramatic for CH3CN, which is about 30 times more abun-dant in the PDR than in the dense core! Grain surfacechemistry has to be invoked to explain the large inferredabundances. Indeed, ice mantles around interstellar dustgrains are active, despite the low temperatures. Atoms(e.g., H, D, C, O and N) can be absorbed on the grainsurfaces, migrate and react with other atoms or moleculesforming complex species that can later be desorbed intothe gas-phase. In contrast to other PDRs (like the OrionBar) or protostars, where the temperature of the dustgrains is ≥ 100K, the Horsehead dust grains have toolow temperatures (20−30K) to permit thermal desorptionfrom the ices. The Horsehead PDR therefore offers a cleanenvironment to investigate the role of photo-desorption.These results are used by the team of the Meudon PDRcode to constrain the grain surface chemistry, which theyare currently implementing in their chemical model (LeBourlot et al. 2012).

A long list of discoveries driven by incredible in-strumental progress and many talented people: TheHorsehead nebula is thus not only a beautiful object, butalso a fantastic physics and chemistry laboratory to studythe interaction between the far-UV radiation and the gasand dust at the edge of molecular clouds. For a decadenow, we have systematically studied the western edge ofthe Horsehead nebula because its geometry is well under-stood and quite simple (almost 1D and viewed edge-on).The density profile across the PDR is well constrainedand there are several current efforts to constrain the ther-mal profile. The combination of low distance to Earth

1The attribution must still be spectroscopically confirmed.

(400 pc), low illumination (χ ∼ 60) and high density (n ∼

105 cm−3) implies that all the interesting physical andchemical processes can be probed in a field-of-view of lessthan 50′′ with typical spatial scales ranging between 1 and10′′.

The development of this project followed the instrumentalprogress in radioastronomy (Graatier & Pety 2012). Forinstance, the recent upgrade of the heterodyne spectrom-eters at the IRAM-30m now enable to observe simultane-ously a bandwidth of 16GHz per polarization at 195 kHzresolution. It allows one to observe in one week whatwould have required one year before! We used this oppor-tunity to setup the Horsehead WHISPER2 project, partlydisplayed in Fig. 1. The recent results described here arederived from this complete unbiased line survey of the 3,2, and 1mm bands at the PDR and dense core positions.

The advent of wideband, high spectral resolution receiversalmost turns any observation into an unbiased spectralsurvey. This opens new possibilities to classify the differ-ent kinds of gas in the universe, based on the moleculesthey contain. In this framework, the WHISPER spectracould become templates for low mass dense cores and lowUV illumination PDRs. Another future thread of workwill be to use innovative observing techniques, like interfer-ometric On-The-Fly (Pety & Rodrıguez-Fernandez 2010),in order to image the Horsehead’s mane with ALMA orNOEMA3 at a resolution of 1′′, enabling to resolve all thephysical and chemical gradients.

The collection of discoveries on the Horsehead is the resultof the effort of many talented scientists. While acknowl-edging them by citing their work, I want to particularlythank my closest collaborators on this project: M. Gerin,J. R. Goicoechea, P. Gratier, V. Guzman, and E. Roueff.

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Bowler, B. P., Waller, W. H., Megeath, S. T., Patten, B. M., &

Tamura, M. 2009, aj, 137, 3685

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A&A, 491, 797

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Goicoechea, J. R., Pety, J., Gerin, M., Hily-Blant, P., & Le Bourlot,

J. 2009, A&A, 498, 771

Goicoechea, J. R., Pety, J., Gerin, M., et al. 2006, A&A, 456, 565

2“Wideband High-resolution Iram-30m Surveys at two Positions

with Emir Receivers”. Thanks to H. S. Liszt for finding this neat

acronym.3NOEMA is the on-going project of extension of the IRAM

Plateau de Bure Interferometer. Details can be found here:

http://iram-institute.org/medias/uploads/NoemaBrochureEngFinal.pdf

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Gratier, P. & Pety, J. 2012, in SF2A-2012: Proceedings of the An-

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Figure 2: The Horsehead nebula imaged with the VLT inB,V,R filters. Courtesy ESO.

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10

Perspective

Formation of Globular Clusters

by Bruce G. Elmegreen

Young massive clusters (YMCs; Portegies Zwart et al.2010) form in regions with high star formation rates aspart of a power law distribution of cluster masses (e.g.,Lim et al. 2013), suggesting that their formation processis not significantly different from that of lower mass clus-ters. The power law appears to reflect turbulent fragmen-tation in interstellar gas. After a Hubble time of evolution,YMCs should resemble old globular clusters (GCs; Whit-more & Schweizer 1995; Meurer et al. 1995; Figure 1),so it is often assumed that most GCs formed in normalstar-forming regions when galaxies were young.

A number of questions emerge from this simple picture.GCs have internal variations in stellar abundances (Car-retta et al. 2010a, Gratton et al. 2012), multiple mainsequences and turnoffs (Bedin et al. 2004), and multiplesubgiant branches (Milone et al. 2008), suggesting self-enrichment by AGB stellar wind debris (Vesperini et al.2013) or debris from fast-rotating stars (Charbonnel et al.2013), and suggesting extended formation times (Keller etal. 2012, Rubele et al. 2013). This type of enrichmentseems to be characteristic of massive clusters in general(Bekki 2011), as young massive clusters in the LMC ap-pear to have it too (Milone et al. 2009, Keller et al. 2011,Rubele et al. 2011) while some lower mass clusters donot (Bragaglia et al. 2012). Self-enrichment is not ob-servable for clusters in regions of star formation, becausethey are too young and most are too low in mass. Also,self-enrichment is more easily detected at low metallicities.Observations of AGB winds in ∼ 100 Myr old clusters inthe Milky Way would be interesting, as would recurring

star formation in clusters this old. One issue is that classi-cal GCs appear to have had this enriched gas mixed withmore primitive gas (D’Ercole et al. 2008, Ventura et al.2009, Schaerer et al. 2011). How that gas got into thecluster and whether today’s ISM can return to a clusterand mix with debris from stellar evolution is an open ques-tion (Bekki & Mackey 2009, Pflamm-Altenburg & Kroupa2009, Conroy & Spergel 2011). Internal rotation of a clus-ter may be a clue to the accretion process (Mackey et al.2013).

The high level of enrichment in GCs implies that the initialcluster mass might have been 10 times larger than whatwe see today, with most of the additional stars evaporatinginto the field (Conroy 2012). However the Fornax dwarf(Larson et al. 2012) has a mass in metal-poor stars thatexceeds the current mass in GCs by only a factor of 4 or 5,so these clusters could not have been much more massivein the past. Also, the total stellar mass in the WLM dwarfgalaxy was about the same as the current mass of its GCwhen the GC formed (∼ 106 M⊙; Hodge et al. 1999;Stephens et al. 2006; Leaman et al. 2012; Elmegreen etal. 2012), so if the GC were 10 times more massive inthe past, then it would have been 91% of the total galaxymass. WLM with its GC is shown in Figure 2.

Figure 1: An infrared image of the massive globularcluster 47 Tuc in the Small Magellanic Cloud taken byVISTA at ESO’s Paranal Observatory. Credit: ESO/M.-R. Cioni/VISTA Magellanic Cloud survey. Acknowledg-ment: Cambridge Astronomical Survey Unit

A second outstanding problem about GC formation is theorigin of the log-normal GC mass distribution. An initial

11

power law or Schechter function changes to something likea log-normal after the low mass clusters disperse. Theselow mass clusters are the first to get destroyed by internalevolution (McLaughlin & Fall 2008), shear (de Grijs & An-ders 2012), and random tidal forces (Gieles et al. 2006).When this transformation took place is not known. Itcould have happened slowly over a Hubble time, as wouldbe the case for evaporation and collisions with the hostgalaxy (Chandar et al. 2007), it could have happenedat birth by rapid unbinding when the gas initially left(”infant mortality,” Parmentier et al. 2008, Baumgardt2008), or it could have happened during the first part ofthe clusters’ lives as the associated star-forming complexdispersed, causing the clusters to be exposed to locallyhigh tidal forces from dense cloud debris and other clus-ters (Elmegreen 2010; called the ”cruel cradle effect” byKruijssen et al. 2012a). The early loss of low-mass clus-ters produces something like a log-normal mass functionwith a peak that either remains constant (Vesperini 1998)or increases slowly over a Hubble time (Kruijssen et al.2012b), depending on the environment.

GC populations are usually bimodal with one componentrelatively blue and low metallicity (Z < 0.1), and the otherrelatively red and higher metallicity (Brodie & Strader2006, Brodie et al. 2012). Blue GCs tend to be in galaxyhalos and extend to larger radii than red GCs (Schuberthet al. 2010; Hargis & Rhode 2012), and the blue GCs are20% larger (Webb et al. 2012). Blue GCs are sometimesslightly older than red GCs as well (Park et al. 2012,Cezario et al. 2013), although both are generally old. Aplausible explanation for this difference in type is thatmost blue GCs formed in dwarf galaxies where the metal-licity is low, and they entered the halos of larger galaxiesduring cosmological accretion (Lee et al. 2010, Forbes &Bridges 2010; Elmegreen 2012; Katz & Ricotti 2012; Parket al. 2012, Tonini 2013). The dwarfs have since dispersedby tidal forces, although many GCs still have either dwarfgalaxy remnants or tidal streams around them (e.g., DaCosta & Armandroff 1995, Mackey et al. 2010). Red GCstend to be associated with galaxy disks and bulges, andthe inner regions of ellipticals. This implies they couldhave formed during disk and bulge formation (Shapiro etal. 2010), acquiring the higher metallicities of their moremassive hosts. Both the blue and the red GCs get intoellipticals along with their spiral host stars during majormergers, and new red GCs form during these mergers ifthe hosts have enough gas (Ashman & Zepf 1992).

There are other possible origins for GCs, other than nor-mal star-forming regions. Some are likely to be the nu-clei of dwarf galaxies (Kruijssen & Cooper 2012, Cohen& Kirby 2012, Capuzzo-Dolcetta 2013, Joo & Lee 2013).The larger GCs may have formed by cluster coalescence(Bruns et al. 2011, Carretta et al 2010b).

Figure 2: WLM local dwarf galaxy with indicated GCmost recently studied by Hodge et al. (1999) andStephens et al. (2006). This is a metal-poor GC withabout 106 M⊙ and still connected with its host dwarfgalaxy, presumably because both are on the outskirtsof the Local Group and have not yet been captured byM31 or the Milky Way. When the WLM GC formed, itcontained a high fraction of the total stellar mass in thegalaxy at that time (Leaman et al. 2012; Elmegreen etal. 2012). Metal poor GCs may be delivered to galaxyhalos as remnants of past star bursts in small dwarfgalaxies like WLM. The image is from the webpageof the LITTLE THINGS survey; red is HI, green isV-band and blue is GALEX FUV (Hunter et al. 2012).(https://science.nrao.edu/science/surveys/littlethings/data/wlm.html)

Can GCs be observed at the time of their formation?A young GC forming 12 Gyrs ago would have its high-redshift counterpart at z = 3.8. If its absolute g-band ABmagnitude is -14.3 for 106 M⊙ at 10 Myr old (Bruzual &Charlot 2003; with metallicity 0.2 solar and a ChabrierIMF), then its apparent AB magnitude at the redshiftedwavelength of 2.4µm would be 31.7, which is marginallynot observable with present-day instruments. However,the entire star-forming region, which most likely containsmany other clusters and unbound OB associations, should

12

be observable. For a typical dn/dM ∼ M−2 cluster massfunction, the total cluster mass down to 10 M⊙ that isassociated with a largest cluster mass of 106 M⊙ is 1.2 ×107 M⊙. If an equal mass is in unclustered stars, then thetotal luminosity would be 24 times that of the largest clus-ter, and the apparent magnitude 28.2, which is observablein deep surveys. For the red GCs, the place to look wouldbe the giant star-forming clumps in very young galaxydisks (Shapiro et al. 2010). The blue GCs would presum-ably be in the dwarf galaxies at that time. Because high-redshift starburst dwarfs generally emit Lyman−α radi-ation through their short disk path-lengths, metal-poorGCs should be found among the class of galaxies calledLyman−α emitters (Elmegreen et al. 2012).

Research on globular clusters has never been more excit-ing than it is now. New surveys (SLUGGS; Usher et al.2012), instruments capable of getting GC spectra in a largesample of galaxies, wide-field cameras capable of findingtens of thousands of GCs in fields around massive galax-ies, deep surveys able to see the halo streams that deliverGCs to galaxies, and numerical simulations with numbersof particles comparable to the number of stars in a GC,are all advancing GC research at rapid pace.

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13

Abstracts of recently accepted papers

The dramatic change of the fossil magnetic field of HD 190073: evidence of the birth ofthe convective core in a Herbig star?

E. Alecian1, C. Neiner1, S. Mathis2,1, C. Catala1, O. Kochukhov3, J. Landstreet4,5, and the MiMeScollaboration

1 LESIA-Observatoire de Paris, CNRS, UPMC Univ., Univ. Paris-Diderot, 5 place Jules Janssen, F-92195 MeudonPrincipal Cedex, France2 Laboratoire AIM, CEA/DSM, CNRS, Universite Paris Diderot, IRFU/SAp Centre de Saclay, F-91191 Gif-sur-Yvette,France3 Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden4 Armagh Observatory, College Hill, Armagh, BT61 9DG, Northern Ireland, UK5 Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, N6A 3K7, Canada

E-mail contact: evelyne.alecian at obspm.fr

In the context of the ESPaDOnS and Narval spectropolarimetric surveys of Herbig Ae/Be stars, we discovered andthen monitored the magnetic field of HD 190073 over more than four years, from 2004 to 2009. Our observations alldisplayed similar Zeeman signatures in the Stokes V spectra, indicating that HD 190073 hosted an aligned dipole,stable over many years, consistent with a fossil origin. We obtained new observations of the star in 2011 and 2012 anddetected clear variations of the Zeeman signature on timescales of days to weeks, indicating that the configuration ofits field has changed between 2009 and 2011. Such a sudden change of external structure of a fossil field has neverpreviously been observed in any intermediate or high-mass star. HD 190073 is an almost entirely radiative pre-mainsequence star, probably hosting a growing convective core. We propose that this dramatic change is the result of theinteraction between the fossil field and the ignition of a dynamo field generated in the newly-born convective core.

Accepted by A&A

http://arxiv.org/pdf/1301.1804

WISE photometry of EXor sources and candidates

S. Antoniucci1, T. Giannini1 and D. Lorenzetti1

1 INAF-Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone (RM), Italy

E-mail contact: simone.antoniucci at oa-roma.inaf.it

We present a collection of WISE photometry of EXor sources and candidates (more recently identified). This representsthe first complete survey of such objects in the mid-IR (3.4 - 22 um) that was carried out with the same instrumentation.Two-color diagrams constructed with WISE data evidence a clear segregation between classical and newly identifiedsources, being these latter characterized by colder (and less evolved) circumstellar disks. By combining 2MASS andWISE data, we obtain spectral energy distributions (SED’s) that are compatible with the existence of an inner holein the circumstellar disk. A compilation of all EXor observations given in the literature at wavelengths very similar tothose of WISE is also provided. This allows us to study their mid-IR variability, which has been poorly investigatedso far and without any coordination with shorter wavelengths surveys. The presented it WISE photometry and thecompilation of the literature data are intended as a first step toward the construction of a significant database in thisspectral regime. Preliminary indications on the mechanisms responsible for the luminosity fluctuations are provided.

Accepted by New Astronomy

http://arxiv.org/pdf/1209.0485v2

14

The Effect of Magnetic Fields and Ambipolar Diffusion on Core Mass Functions

Nicole D. Bailey1 and Shantanu Basu1

1 Department of Physics and Astronomy, University of Western Ontario,1151 Richmond Street, London, Ontario, N6A 3K7, Canada

E-mail contact: nwityk at uwo.ca

Linear analysis of the formation of protostellar cores in planar magnetic interstellar clouds yields information aboutlength scales involved in star formation. Combining these length scales with various distributions of other environ-mental variables, (i.e., column density and mass-to-flux ratio) and applying Monte Carlo methods allow us to producesynthetic core mass functions (CMFs) for different environmental conditions. Our analysis shows that the shape ofthe CMF is directly dependent on the physical conditions of the cloud. Specifically, magnetic fields act to broaden themass function and develop a high-mass tail while ambipolar diffusion will truncate this high-mass tail. In addition,we analyze the effect of small number statistics on the shape and high-mass slope of the synthetic CMFs. We findthat observed core mass functions are severely statistically limited, which has a profound effect on the derived slopefor the high-mass tail.

Accepted by Astrophysical Journal


A Thermal Infrared Imaging Study of Very Low-Mass, Wide Separation Brown DwarfCompanions to Upper Scorpius Stars: Constraining Circumstellar Environments

Vanessa Bailey1, Philip M. Hinz1, Thayne Currie2, Kate Y.L. Su1, Simone Esposito3, John M. Hill4,William F. Hoffmann1, Terry Jones5, Jihun Kim6, Jarron Leisenring7, Michael Meyer7, Ruth Murray-Clay8, Matthew J. Nelson9, Enrico Pinna3, Alfio Puglisi3, George Rieke1, Timothy Rodigas1, AndrewSkemer1, Michael F. Skrustkie9, Vidhya Vaitheeswaran1, and John C. Wilson9

1 Steward Observatory, University of Arizona, Tucson, AZ, USA2 Department of Astronomy and Astrophysics, University of Toronto, Toronto, Ontario, Canada3 INAF, Osservatorio di Arcetri, Firenze, Italy4 Large Binocular Telescope, University of Arizona, Tucson, AZ, USA5 School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, USA6 College of Optical Sciences, University of Arizona, Tucson, AZ, USA7 Institute for Astronomy, ETH Zurich, Zurich, Switzerland8 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA9 Department of Astronomy, University of Virginia, Charlottesville, VA, USA

E-mail contact: vbailey at as.arizona.edu

We present a 3 − 5 µm LBT/MMT adaptive optics imaging study of three Upper Scorpius stars with brown dwarf(BD) companions with very low-masses/mass ratios (MBD < 25 MJup; MBD/M⋆ ≈ 1–2%), and wide separations(300−700AU): GSC 06214, 1RXS 1609, and HIP 78530. We combine these new thermal IR data with existing 1−4 µmand 24 µm photometry to constrain the properties of the BDs and identify evidence for circumprimary/secondary disksin these unusual systems. We confirm that GSC 06214B is surrounded by a disk, further showing this disk produces abroadband IR excess due to small dust near the dust sublimation radius. An unresolved 24 µm excess in the systemmay be explained by the contribution from this disk. 1RXS 1609B exhibits no 3− 4 µm excess, nor does its primary;however, the system as a whole has a modest 24 µm excess, which may come from warm dust around the primaryand/or BD. Neither object in the HIP 78530 system exhibits near- to mid-IR excesses. We additionally find that the1 − 4 µm colors of HIP 78530B match a spectral type of M3 ± 2, inconsistent with the M8 spectral type assignedbased on its near-IR spectrum, indicating it may be a low-mass star rather than a BD. We present new upper limitson additional low-mass companions in the system (< 5 MJup beyond 175 AU). Finally, we examine the utility ofcircumsecondary disks as probes of the formation histories of wide BD companions, finding that the presence of a diskmay disfavor BD formation near the primary with subsequent outward scattering.

Accepted by The Astrophysical Journal


15

Lopsided dust rings in transition disks

T. Birnstiel1,2, C. P. Dullemond3 and P. Pinilla3

1 Excellence Cluster Universe, Technische Universitat Munchen, Boltzmannstr. 2, 85748 Garching, Germany2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA3 Heidelberg University, Center for Astronomy (ZAH), Institute for Theoretical Astrophysics, Albert Ueberle Str. 2,69120 Heidelberg, GermanyE-mail contact: tbirnstiel at cfa.harvard.edu

Context: Particle trapping in local or global pressure maxima in protoplanetary disks is one of the new paradigms inthe theory of the first stages of planet formation. However, finding observational evidence for this effect is not easy.Recent work suggests that the large ring-shaped outer disks observed in transition disk sources may in fact be lopsidedand constitute large banana-shaped vortices.Aims: We wish to investigate how effectively dust can accumulate along the azimuthal direction. We also want to findout if the size-sorting resulting from this accumulation can produce detectable signatures at millimeter wavelengths.Methods: To keep the numerical cost under control we developed a 1+1D method in which the azimuthal variations aretreated separately from the radial variations. The azimuthal structure was calculated analytically for a steady-statebetween mixing and azimuthal drift. We derived equilibration time scales and compared the analytical solutions totime-dependent numerical simulations.Results: We found that weak, but long-lived azimuthal density gradients in the gas can induce very strong azimuthalaccumulations of dust. The strength of the accumulations depends on the Peclet number, which describes the relativeimportance of advection and diffusion. We applied our model to transition disks and our simulated observations showthat this effect would be easily observable with the Atacama Large Millimeter/submillimeter Array (ALMA) and couldbe used to put constraints on the strength of turbulence and the local gas density.

Accepted by A&A

http://goo.gl/4ysxE

Influence of viscosity and the adiabatic index on planetary migration

Bertram Bitsch1,2, Aaron Boley3 and Wilhelm Kley1

1 Institut fur Astronomie & Astrophysik, Universitat Tubingen, Auf der Morgenstelle 10, D-72076 Tubingen, Germany2 Dep. Cassiopee, University of Nice-Sophia Antipolis, CNRS, Observatoire de la Cote d’Azur, 06304, Nice3 University of Florida, Department of Astronomy, 211 Bryant Space Science Center, Gainesville, FL 32611, USAE-mail contact: bertram.bitsch at oca.eu

Context. The strength and direction of migration of low mass embedded planets depends on the disk’s thermodynamicstate. It has been shown that in active disks, where the internal dissipation is balanced by radiative transport, migrationcan be directed outwards, a process which extends the lifetime of growing embryos. Very important parametersdetermining the structure of disks, and hence the direction of migration, are the viscosity and the adiabatic index.Aims. In this paper we investigate the influence of different viscosity prescriptions (α-type and constant) and adiabaticindices on disk structures. We then determine how this affects the migration rate of planets embedded in such disks.Methods. We perform three-dimensional numerical simulations of accretion disks with embedded planets. We use theexplicit/implicit hydrodynamical code NIRVANA that includes full tensor viscosity and radiation transport in theflux-limited diffusion approximation, as well as a proper equation of state for molecular hydrogen. The migration ofembedded 20 MEarth planets is studied.Results. Low-viscosity disks have cooler temperatures and the migration rates of embedded planets tend toward theisothermal limit. Hence, in these disks, planets migrate inwards even in the fully radiative case. The effect of outwardmigration can only be sustained if the viscosity in the disk is large. Overall, the differences between the treatmentsfor the equation of state seem to play a more important role in disks with higher viscosity. A change in the adiabaticindex and in the viscosity changes the zero-torque radius that separates inward from outward migration.Conclusions. For larger viscosities, temperatures in the disk become higher and the zero-torque radius moves to largerradii, allowing outward migration of a 20-MEarth planet to persist over an extended radial range. In combination withlarge disk masses, this may allow for an extended period of the outward migration of growing protoplanetary cores.

Accepted by A&A


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Orbital Migration of Protoplanets in a Marginally Gravitationally Unstable Disk

Alan P. Boss1

1 Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington,DC 20015-1305, USA

E-mail contact: boss at dtm.ciw.edu

Core accretion and disk instability require giant protoplanets to form in the presence of disk gas. Protoplanet migrationmodels generally assume disk masses low enough that the disk’s self-gravity can be neglected. However, disk instabilityrequires a disk massive enough to be marginally gravitationally unstable (MGU). Even for core accretion, a FU Orionisoutburst may require a brief MGU disk phase. We present a new set of three dimensional, gravitational radiationhydrodynamics models of MGU disks with multiple protoplanets, which interact gravitationally with the disk andwith each other, including disk gas mass accretion. Initial protoplanet masses are 0.01 to 10 M⊕ for core accretionmodels, and 0.1 to 3 MJup for Nice scenario models, starting on circular orbits with radii of 6, 8, 10, or 12 AU, insidea 0.091 M⊙ disk extending from 4 to 20 AU around a 1M⊙ protostar. Evolutions are followed for up to ∼ 4000 yr andinvolve phases of relative stability (e ∼ 0.1) interspersed with chaotic phases (e ∼ 0.4) of orbital interchanges. The0.01 to 10 M⊕ cores can orbit stably for ∼ 1000 yr: monotonic inward or outward orbital migration of the type seenin low mass disks does not occur. A system with giant planet masses similar to our Solar System (1.0, 0.33, 0.1, 0.1MJup) was stable for over 1000 yr, and a Jupiter-Saturn-like system was stable for over 3800 yr, implying that ourgiant planets might well survive a MGU disk phase.

Accepted by ApJ

http://www.dtm.ciw.edu/users/boss/ftp/orbital.pdf

Collapse and Fragmentation of Magnetic Molecular Cloud Cores with the Enzo AMRMHD Code. I. Uniform Density Sphere

Alan P. Boss and Sandra A. Keiser

1 Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington,DC 20015-1305, USA

E-mail contact: boss at dtm.ciw.edu

Magnetic fields are important contributers to the dynamics of collapsing molecular cloud cores, and can have a majoreffect on whether collapse results in a single protostar or fragmentation into a binary or multiple protostar system.New models are presented of the collapse of magnetic cloud cores using the adaptive mesh refinement (AMR) codeEnzo2.0. The code was used to calculate the ideal magnetohydrodynamics (MHD) of initially spherical, uniformdensity and rotation clouds with density perturbations, i.e., the Boss and Bodenheimer (1979) standard isothermaltest case for three dimensional (3D) hydrodynamics (HD) codes. After first verifying that Enzo reproduces the binaryfragmentation expected for the non-magnetic test case, a large set of models was computed with varied initial magneticfield strengths and directions with respect to the cloud core axis of rotation (parallel or perpendicular), density per-turbation amplitudes, and equations of state. Three significantly different outcomes resulted: (1) contraction withoutsustained collapse, forming a denser cloud core, (2) collapse to form a single protostar with significant spiral arms,and (3) collapse and fragmentation into binary or multiple protostar systems, with multiple spiral arms. Comparisonsare also made with previous MHD calculations of similar clouds with barotropic equations of state. These results forthe collapse of initially uniform density spheres illustrate the central importance of both magnetic field direction andfield strength for determining the outcome of dynamic protostellar collapse.

Accepted by ApJ


The RMS Survey: Near-IR Spectroscopy of Massive Young Stellar Objects

H. D. B. Cooper1, S. L. Lumsden1, R. D. Oudmaijer1, M. G. Hoare1, A. J. Clarke1, J. S. Urquhart2,J. C. Mottram3, T. J. T. Moore4 and B. Davies4

1 School of Physics & Astronomy, University of Leeds, Leeds, LS2 9JT, UK

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2 Max-Planck-Institut fr Radioastronomie, 53121 Bonn, Germany3 Leiden Observatory, Leiden University, 2300 RA, Leiden, Netherlands4 Astrophysics Research Institute, Liverpool JohnMoores University, Twelve Quays House, EgertonWharf, BirkenheadCH41 1LD, UK

E-mail contact: pyhdc at leeds.ac.uk

Near-infrared H- and K-band spectra are presented for 247 objects, selected from the Red MSX Source (RMS) surveyas potential young stellar objects (YSOs). 195 (∼ 80%) of the targets are YSOs, of which 131 are massive YSOs(LBOL > 5 × 103 L⊙, M > 8 M⊙). This is the largest spectroscopic study of massive YSOs to date, providing avaluable resource for the study of massive star formation. In this paper we present our exploratory analysis of thedata. The YSOs observed have a wide range of embeddedness (2.7 < AV < 114), demonstrating that this studycovers minimally obscured objects right through to very red, dusty sources. Almost all YSOs show some evidence foremission lines, though there is a wide variety of observed properties. The most commonly detected lines are Br γ, H2,fluorescent Fe II, CO bandhead, [Fe II] and He I 2–1 1S–1P, in order of frequency of occurrence. In total, ∼ 40% of theYSOs display either fluorescent Fe II 1.6878 µm or CO bandhead emission (or both), indicative of a circumstellar disc;however, no correlation of the strength of these lines with bolometric luminosity was found. We also find that ∼ 60%of the sources exhibit [Fe II] or H2 emission, indicating the presence of an outflow. Three quarters of all sources haveBr γ in emission. A good correlation with bolometric luminosity was observed for both the Br γ and H2 emissionline strengths, covering 1 L⊙ < LBOL < 3.5 × 105 L⊙. This suggests that the emission mechanism for these lines isthe same for low-, intermediate-, and high-mass YSOs, i.e. high-mass YSOs appear to resemble scaled-up versions oflow-mass YSOs.

Accepted by MNRAS


From Planetesimals to Dust: Low Gravity Experiments on Recycling Solids at the InnerEdge of Protoplanetary Disks

Caroline de Beule, Thorben Kelling, Gerhard Wurm, Jens Teiser and Tim Jankowski

1 Universitat Duisburg-Essen, Fakultat fur Physik, Lotharstraβe 1,D-47057 Duisburg, Germany

E-mail contact: caroline.de-beule at uni-due.de

Transporting solids of different sizes is an essential process in the evolution of protoplanetary disks and planet for-mation. Large solids are supposed to drift inward; high-temperature minerals found in comets are assumed to havebeen transported outward. From low-gravity experiments on parabolic flights we studied the light-induced erosionof dusty bodies caused by a solid-state greenhouse effect and photophoresis within a dust bed’s upper layers. Thegravity levels studied were 0.16g, 0.38g, 1g, and 1.7g. The light flux during the experiments was 12 ± 2 kW m−2 andthe ambient pressure was 6 ± 0.9 mbar. Light-induced erosion is strongly gravity dependent, which is in agreementwith a developed model. In particular for small dusty bodies ((sub)-planetesimals), efficient erosion is possible at theoptically thin inner edges of protoplanetary disks. Light-induced erosion prevents significant parts of a larger bodyfrom moving too close to the host star and be being subsequently accreted. The small dust produced continues to besubject to photophoresis and is partially transported upward and outward over the surface of the disk; the resultingsmall dust particles observed over the disk’s lifetime. The fraction of eroded dust participates in subsequent cycles ofgrowth during planetesimal formation. Another fraction of dust might be collected by a body of planetary size if thisbody is already present close to the disk edge. Either way, light induced erosion is an efficient recycling process inprotoplanetary disks.

Accepted by ApJ


Search for Associations Containing Young stars (SACY): Chemical tagging IC 2391 &the Argus association

G. M. De Silva1, V. D’Orazi2,6, C. Melo3, C. A. O. Torres4, M. Gieles5,7, G. R. Quast4, M. Sterzik3

1 Australian Astronomical Observatory, 105 Delhi Rd, NSW 2113, Australia

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2 Macquarie University Research Centre in Astronomy, Astrophysics & Astrophotonics NSW 2109, Australia; Depart-ment of Physics & Astronomy, Macquarie University, NSW 2109, Australia3 European Southern Observatory, Casilla 19001, Santiago 19, Chile4 Laboratorio Nacional de Astrofısica/MCT, 37504-364, Itajuba, Brazil5 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK6 Monash Centre for Astrophysics, School of Mathematical Sciences, Building 28, Monash University, VIC 3800, Aus-tralia7 Department of Physics, University of Surrey, Guildford, GU2 7XH, UK

E-mail contact: gdesilva at aao.gov.au

We explore the possible connection between the open cluster IC 2391 and the unbound Argus association identifiedby the SACY survey. In addition to common kinematics and ages between these two systems, here we explore theirchemical abundance patterns to confirm if the two substructures shared a common origin. We carry out a homogenoushigh-resolution elemental abundance study of eight confirmed members of IC 2391 as well as six members of the Argusassociation using UVES spectra. We derive spectroscopic stellar parameters and abundances for Fe, Na, Mg, Al, Si,Ca, Ti, Cr, Ni and Ba.All stars in the open cluster and Argus association were found to share similar abundances with the scatter wellwithin the uncertainties, where [Fe/H] = −0.04 ± 0.03 for cluster stars and [Fe/H] = −0.06 ± 0.05 for Argus stars.Effects of over-ionisation/excitation were seen for stars cooler than roughly 5200K as previously noted in the literature.Also, enhanced Ba abundances of around 0.6 dex were observed in both systems. The common ages, kinematics andchemical abundances strongly support that the Argus association stars originated from the open cluster IC 2391.Simple modeling of this system find this dissolution to be consistent with two-body interactions.

Accepted by MNRAS


The Luminosities of Protostars in the Spitzer c2d and Gould Belt Legacy Clouds

Michael M. Dunham1, Hector G. Arce1, Lori E. Allen2, Neal J. Evans II3, Hannah Broekhoven-Fiene4,Nicholas L. Chapman5, Lucas A. Cieza6, Robert A. Gutermuth7, Paul M. Harvey3, Jennifer Hatchell8,Tracy L. Huard9, Jason M. Kirk10, Brenda C. Matthews4, Bruno Merın11, Jennifer F. Miller9,12, DawnE. Peterson13 and Loredana Spezzi14

1 Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520, USA2 National Optical Astronomy Observatories, Tucson, AZ, USA3 Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205,USA 4 Herzberg Institute, National Research Council of Canada, 5071 W. Saanich Road, Victoria, BC V9E 2E7,Canada5 Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Department of Physics & Astron-omy, 2145 Sheridan Road, Evanston, IL 60208, USA6 Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822, USA7 Department of Astronomy, University of Massachusetts, Amherst, MA, USA8 Astrophysics Group, Physics, University of Exeter, Exeter EX4 4QL, UK9 Department of Astronomy, University of Maryland, College Park, MD 20742, USA10 School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF24 3AA, UK11 Herschel Science Centre, ESAC-ESA, P.O. Box 78, 28691 Villanueva de la Canada, Madrid, Spain12 HarvardSmithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA13 Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 8030114 European Southern Observatory (ESO), Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen, Germany

E-mail contact: michael.dunham at yale.edu

Motivated by the long-standing “luminosity problem” in low-mass star formation whereby protostars are underlumi-nous compared to theoretical expectations, we identify 230 protostars in 18 molecular clouds observed by two Spitzer

Space Telescope Legacy surveys of nearby star-forming regions. We compile complete spectral energy distributions,calculate Lbol for each source, and study the protostellar luminosity distribution. This distribution extends over threeorders of magnitude, from 0.01 L⊙ – 69 L⊙, and has a mean and median of 4.3 L⊙ and 1.3 L⊙, respectively. The

19

distributions are very similar for Class 0 and Class I sources except for an excess of low luminosity (Lbol < 0.5 L⊙)Class I sources compared to Class 0. 100 out of the 230 protostars (43%) lack any available data in the far-infraredand submillimeter (70 µm < λ < 850 µm) and have Lbol underestimated by factors of 2.5 on average, and up tofactors of 8− 10 in extreme cases. Correcting these underestimates for each source individually once additional databecomes available will likely increase both the mean and median of the sample by 35% – 40%. We discuss and com-pare our results to several recent theoretical studies of protostellar luminosities and show that our new results do notinvalidate the conclusions of any of these studies. As these studies demonstrate that there is more than one plausibleaccretion scenario that can match observations, future attention is clearly needed. The better statistics provided byour increased dataset should aid such future work.

Accepted by Astron. J.


Magnetized Accretion and Dead Zones in Protostellar Disks

Natalia Dzyurkevich1,3, Neal J. Turner2, Thomas Henning3 and Wilhelm Kley4

1 Laboratoire de radioastronomie, UMR 8112 du CNRS, Ecole Normale Superieure et Observatoire de Paris, 24 ruede Lhomond, 75231, Paris Cedex 05, France2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA3 Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg, Germany4 University of Tuebingen, Auf der Morgenstelle 10, Tuebingen, 72076 Germany

E-mail contact: natalia.dzyurkevich at lra.ens.fr

The edges of magnetically-dead zones in protostellar disks have been proposed as locations where density bumps mayarise, trapping planetesimals and helping form planets. Magneto-rotational turbulence in magnetically-active zonesprovides both accretion of gas on the star and transport of mass to the dead zone. We investigate the location ofthe magnetically-active regions in a protostellar disk around a solar-type star, varying the disk temperature, surfacedensity profile, and dust-to-gas ratio. We also consider stellar masses between 0.4 and 2 M⊙, with correspondingadjustments in the disk mass and temperature. The dead zone’s size and shape are found using the Elsasser numbercriterion with conductivities including the contributions from ions, electrons, and charged fractal dust aggregates. Thecharged species’ abundances are found using the approach proposed by Okuzumi. The dead zone is in most casesdefined by the ambipolar diffusion. In our maps, the dead zone takes a variety of shapes, including a fish-tail pointingaway from the star and islands located on and off the midplane. The corresponding accretion rates vary with radius,indicating locations where the surface density will increase over time, and others where it will decrease. We show thatdensity bumps do not readily grow near the dead zone’s outer edge, independently of the disk parameters and the dustproperties. Instead, the accretion rate peaks at the radius where the gas-phase metals freeze out. This could lead toclearing a valley in the surface density, and to a trap for pebbles located just outside the metal freeze-out line.

Accepted by ApJ

http://arxiv.org/pdf/1301.1487v2

Testing maser-based evolutionary schemes: A new search for 37.7-GHz methanol masers

Simon Ellingsen1, Shari Breen2, Maxim Voronkov2 and Joanne Dawson1

1 School of Mathematics and Physics, Private Bag 37, University of Tasmania, Hobart 7001, TAS, Australia2 CSIRO Astronomy and Space Science, PO Box 76 Epping, NSW, Australia

E-mail contact: Simon.Ellingsen at utas.edu.au

We have used the Australia Telescope National Facility Mopra 22-m antenna to search for 37.7-GHz (7−2 → 8−1E)methanol masers towards a sample of thirty six class II methanol masers. The target sources are the most luminousclass II methanol masers not previously searched for this transition, with isotropic peak 12.2-GHz maser luminositygreater than 250 Jy kpc2 and isotropic peak 6.7-GHz maser luminosity greater than 800 Jy kpc2. Seven new 37.7-GHzmethanol masers were detected as a result of the search. The detection rate for 37.7-GHz methanol masers towards acomplete sample of all such class II methanol maser sites south of declination -20◦ is at least 30 percent. The relativelyhigh detection rate for this rare methanol transition is in line with previous predictions that the 37.7-GHz transition is

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associated with a late stage of the class II methanol maser phase of high-mass star formation. We find that there is amodest correlation between the ratio of the 6.7- and 37.7-GHz maser peak intensity and the 6.7- and 12.2-GHz maserpeak intensity (correlation coefficient 0.63 in a log-log plot). We detected one new 38.3-GHz (62 → 53A

−) methanolmaser towards G335.789 + 0.174. This is only the fourth source for which maser emission has been detected in thistransition and it is the only one for which emission is not also observed in the 38.5-GHz 62 → 53A

+ transition.

Accepted by MNRAS


The Interior Structure Constants as an Age Diagnostic for Low-Mass, Pre-Main Se-quence Detached Eclipsing Binary Stars

Gregory A. Feiden1 and Aaron Dotter2

1 Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755, USA2 Research School of Astronomy and Astrophysics, The Australian National University, Weston, ACT 2611, Australia

E-mail contact: Gregory.A.Feiden.GR at Dartmouth.edu

We propose a novel method for determining the ages of low-mass, pre-main sequence stellar systems using the apsidalmotion of low-mass detached eclipsing binaries. The apsidal motion of a binary system with an eccentric orbit providesinformation regarding the interior structure constants of the individual stars. These constants are related to thenormalized stellar interior density distribution and can be extracted from the predictions of stellar evolution models.We demonstrate that low-mass, pre-main sequence stars undergoing radiative core contraction display rapidly changinginterior structure constants (greater than 5% per 10 Myr) that, when combined with observational determinations ofthe interior structure constants (with 5 – 10% precision), allow for a robust age estimate. This age estimate, unlikethose based on surface quantities, is largely insensitive to the surface layer where effects of magnetic activity are likelyto be most pronounced. On the main sequence, where age sensitivity is minimal, the interior structure constantsprovide a valuable test of the physics used in stellar structure models of low-mass stars. There are currently noknown systems where this technique is applicable. Nevertheless, the emphasis on time domain astronomy with currentmissions, such as Kepler, and future missions, such as LSST, has the potential to discover systems where the proposedmethod will be observationally feasible.

Accepted by ApJ


On the radio–X-ray connection in young stellar objects in the Orion Nebula Cluster

Jan Forbrich1,2 and Scott J. Wolk2

1 University of Vienna, Department of Astrophysics, Turkenschanzstraße 17, 1180 Vienna, Austria2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

E-mail contact: jan.forbrich at univie.ac.at

Context: Both X-ray and radio observations offer insight into the high-energy processes of young stellar objects (YSOs).The observed thermal X-ray emission can be accompanied by both thermal and nonthermal radio emission. Due tovariability, simultaneous X-ray and radio observations are a priori required, but only a comparably small number ofYSOs have been studied in this way. Results have been inconclusive due to the even smaller number of YSOs thatwere simultaneously detected in X-ray and radio observations.Aims: We use archival X-ray and radio observations of the Orion Nebula Cluster (ONC) to significantly enlarge thesample size of known YSOs with both X-ray and radio detections.Methods: We study the ONC using multi-epoch non-simultaneous archival Chandra X-ray and NRAO Very LargeArray (VLA) single-band radio data. The multiple epochs allow us to reduce the impact of variability by obtainingapproximated quiescent fluxes.Results: We find that only a small fraction of the X-ray sources (7%) have radio counterparts, even if 60% of the radiosources have X-ray counterparts. YSOs with detections in both bands thus constitute a small minority of the cluster.The radio flux density is typically too low to distinguish thermal and nonthermal radio sources. Only a small fractionof the YSOs with detections in both bands are compatible with the empirical “Gudel-Benz” (GB) relation. Most of

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the sources not compatible with the GB relation are proplyds, and thus likely thermal sources, but only a fraction ofthe proplyds is detected in both bands, such that the role of these sources is inconclusive.Conclusions: While the radio sources appear to be globally unrelated to the X-ray sources, the X-ray dataset clearlyis much more sensitive than the radio data. We find tentative evidence that known non-thermal radio sources andsaturated X-ray sources are indeed close to the empirical relation, even if skewed to higher radio luminosities, as theyare expected to be. Most of the sources that are clearly incompatible with the empirical relation are proplyds thatcould instead plausibly be thermal radio sources. The newly expanded Jansky Very Large Array with its significantlyenhanced continuum sensitivity is beginning to provide an ideal tool for addressing this issue. Combined X-ray andradio studies of YSOs using older VLA data are clearly limited by the typically low signal-to-noise of the radiodetections, providing insufficient information to disentangle thermal and nonthermal sources.

Accepted by A&A


The Effect of Irradiation on the Jeans Mass in Fragmenting Self-Gravitating ProtostellarDiscs

Duncan Forgan1 and Ken Rice1

1 Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, Blackford Hill,Edinburgh, EH9 3HJ, Scotland, UK

E-mail contact: dhf at roe.ac.uk

When a self-gravitating disc is subject to irradiation, its propensity to fragmentation will be affected. The strengthof self-gravitating disc stresses is expected to dictate disc fragmentation: as the strength of these torques typicallydecrease with increasing sound speed, it is reasonable to assume, to first-order, that disc fragmentation is suppressedwhen compared to the non-irradiated case, although previous work has shown that the details are complicated bythe source of the irradiation. We expand on previous analysis of the Jeans mass inside spiral structures in self-gravitating discs, incorporating the effects of stellar irradiation and background irradiation. If irradiation is present,fragmentation is suppressed for marginally unstable discs at low accretion rates (compared to the no-irradiation case),but these lower accretion rates correspond to higher mass discs. Fragmentation can still occur for high accretion rates,but is consequently suppressed at lower disc surface densities, and the subsequent Jeans mass is boosted. These resultsfurther bolster the consensus that, without subsequent fragment disruption or mass loss, the gravitational instabilityis more likely to form brown dwarfs and low-mass stars than gas giant planets.

Accepted by MNRAS


An analysis of the deuterium fractionation of star-forming cores in the Perseus molecularcloud

R.K. Friesen1,2, H.M. Kirk3 and Y.L. Shirley4

1 National Radio Astronomy Observatory, 520 Edgemont Rd, Charlottesville VA 22903, USA2 Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St George St, Toronto Canada M5S3H43 Origins Institute, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada, L8S 4M14 Steward Observatory, University of Arizona, 933 N. Cherry Ave.,Tucson, AZ 85721, USA

E-mail contact: friesen at di.utoronto.ca

We have performed a pointed survey of N2D+ 2-1 and N2D

+ 3-2 emission toward 64 N2H+-bright starless and

protostellar cores in the Perseus molecular cloud using the Arizona Radio Observatory Submillimeter Telescope andKitt Peak 12m telescope. We find a mean deuterium fractionation in N2H

+, RD = N(N2D+) /N(N2H

+), of 0.08,with a maximum RD = 0.2. In detected sources, we find no significant difference in the deuterium fractionationbetween starless and protostellar cores, nor between cores in clustered or isolated environments. We compare thedeuterium fraction in N2H

+ with parameters linked to advanced core evolution. We only find significant correlationsbetween the deuterium fraction and increased H2 column density, as well as with increased central core density, for

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all cores. Towards protostellar sources, we additionally find a significant anti-correlation between RD and bolometrictemperature. We show that the Perseus cores are characterized by low CO depletion values relative to previous studiesof star forming cores, similar to recent results in the Ophiuchus molecular cloud. We suggest that the low averageCO depletion is the dominant mechanism that constrains the average deuterium fractionation in the Perseus cores tosmall values. While current equilibrium and dynamic chemical models are able to reproduce the range of deuteriumfractionation values we find in Perseus, reproducing the scatter across the cores requires variation in parameters suchas the ionization fraction or the ortho- to para-H2 ratio across the cloud, or a range in core evolution timescales.

Accepted by ApJ


A three-phase chemical model of hot cores: the formation of glycine

Robin T. Garrod1

1 Center for Radiophysics and Space Research, Cornell University

E-mail contact: rgarrod at astro.cornell.edu

A new chemical model is presented that simulates fully-coupled gas-phase, grain-surface and bulk-ice chemistry inhot cores. Glycine (NH2CH2COOH), the simplest amino acid, and related molecules such as glycinal, propionic acidand propanal, are included in the chemical network. Glycine is found to form in moderate abundance within andupon dust-grain ices via three radical-addition mechanisms, with no single mechanism strongly dominant. Glycineproduction in the ice occurs over temperatures ∼40–120 K. Peak gas-phase glycine fractional abundances lie in therange 8 × 10−11–8 × 10−9, occuring at ∼200 K, the evaporation temperature of glycine. A gas-phase mechanism forglycine production is tested and found insignificant, even under optimal conditions. A new spectroscopic radiative-transfer model is used, allowing the translation and comparison of the chemical-model results with observationsof specific sources. Comparison with the nearby hot-core source NGC 6334 IRS1 shows excellent agreement withintegrated line intensities of observed species, including methyl formate. The results for glycine are consistent with thecurrent lack of a detection of this molecule toward other sources; the high evaporation temperature of glycine rendersthe emission region extremely compact. Glycine detection with ALMA is predicted to be highly plausible, for bright,nearby sources with narrow emission lines. Photodissociation of water and subsequent hydrogen-abstraction fromorganic molecules by OH, and NH2, are crucial to the build-up of complex organic species in the ice. The inclusion ofalternative branches within the network of radical-addition reactions appears important to the abundances of hot-coremolecules; less favorable branching ratios may remedy the anomalously high abundance of glycolaldehyde predictedby this and previous models.

Accepted by ApJ


XMM-Newton monitoring of the close pre-main-sequence binary AK Sco. Evidence oftide driven filling of the inner gap in the circumbinary disk

Ana Ines Gomez de Castro1, Javier Lopez-Santiago2, Antonio Talavera3, A.Yu. Sytov4, and D. Bisikalo4

1 S.D. Astronomıa y Geodesia and Instituto de Matematica Interdisciplinar, Fac. de CC Matematicas, UniversidadComplutense, 28040 Madrid, Spain2 Departamento de Astrofısica, Fac de CC Fısicas, Universidad Complutense, 28040 Madrid, Spain3 European Space Astronomy Center, Madrid, Spain4 Institute of Astronomy of the Russian Academy of Sciences, Moscow, Russia

E-mail contact: aig at mat.ucm.es

AK Sco stands out among pre-main sequence binaries because of its prominent ultraviolet excess, the high eccentricityof its orbit and the strong tides driven by it. AK Sco consists of two F5 type stars that get as close as 11R∗ atperiastron passage. The presence of a dense (ne ∼ 1011 cm−3) extended envelope has been unveiled recently. In thisarticle, we report the results from a XMM-Newton based monitoring of the system. We show that at periastron,X-ray and UV fluxes are enhanced by a factor of ∼ 3 with respect to the apastron values. The X-ray radiationis produced in an optically thin plasma with T∼ 6.4 × 106 K and it is found that the NH column density rises

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from 0.35×1021 cm−2 at periastron to 1.11×1021 cm−2 at apastron, in good agreement with previous polarimetricobservations. The UV emission detected in the Optical Monitor band seems to be caused by the reprocessing of thehigh energy magnetospheric radiation on the circumstellar material. Further evidence of the strong magnetosphericdisturbances is provided by the detection of line broadening of 278.7 km s−1 in the N V line with HST/STIS. Numericalsimulations of the mass flow from the circumbinary disk to the components have been carried out. They providea consistent scenario with which to interpret AK Sco observations. We show that the eccentric orbit acts like agravitational piston. At apastron, matter is dragged efficiently from the inner disk border, filling the inner gap andproducing accretion streams that end as ring-like structures around each component of the system. At periastron, thering-like structures come into contact, leading to angular momentum loss, and thus producing an accretion outburst.

Accepted by ApJ


Variability at the Edge: Optical Near/IR Rapid Cadence Monitoring of Newly Out-bursting FU Orionis Object HBC 722

Joel D. Green1, Paul Roberston1, Giseon Baek2, David Pooley3,4, Soojong Pak1,2, Myungshin Im5,Jeong-Eun Lee5, Yiseul Jeon5, Changsun Choi5 and Stefano Meschiari1

1 Department of Astronomy, 2515 Speedway, University of Texas at Austin, Austin, TX, USA2 School of Space Research, Kyung Hee University, Gyeonggi-Do 446-741, Korea3 Dept. of Physics, Sam Houston State University, Huntsville, TX, USA4 Eureka Scientific, Austin, TX, USA5 CEOU/Department of Physics & Astronomy, Seoul National University, Seoul 151-742, Korea

E-mail contact: joel at astro.as.utexas.edu

We present the detection of day-timescale periodic variability in the r-band lightcurve of newly outbursting FUOrionis-type object HBC 722, taken from > 42 nights of observation with the CQUEAN instrument on the McDonaldObservatory 2.1m telescope. The optical/near-IR lightcurve of HBC 722 shows a complex array of periodic variability,clustering around 5.8 day (0.044 mag amplitude) and 1.28 day (0.016 mag amplitude) periods, after removal of overallbaseline variation. We attribute the unusual number of comparable strength signals to a phenomenon related tothe temporary increase in accretion rate associated with FUors. We consider semi-random “flickering”, magneticbraking/field compression and rotational asymmetries in the disk instability region as potential sources of variability.Assuming the 5.8 day period is due to stellar rotation and the 1.28 day period is indicative of Keplerian rotation atthe inner radius of the accretion disk (at 2 R⋆), we derive a B-field strength of 2.2-2.7 kG, slightly larger than typicalT Tauri stars. If instead the 5.8 day signal is from a disk asymmetry, the instability region has an outer radius of5.4 R⋆, consistent with models of FUor disks. Further exploration of the time domain in this complicated source andrelated objects will be key to understanding accretion processes.

Accepted by Astrophysical Journal


The multiplicity of massive stars in the Orion Nebula Cluster as seen with long-baselineinterferometry

Rebekka Grellmann1, Thomas Preibisch1, Thorsten Ratzka1, Stefan Kraus2, Krzysztof Helminiak3,4

and Hans Zinnecker5,6

1 Universitats-Sternwarte, Ludwig-Maximilians-Universitat Munchen, Scheinerstr. 1, 81679 Munchen, Germany2 University of Michigan, Department of Astronomy, Ann Arbor, MI 48109-1090, USA3 Departamento de Astronoma y Astrofisica, Pontificia Universidad Catlica de Chile, Av. Vicua Mackenna 4860,7820436 Macul, Santiago, Chile4 Nicolaus Copernicus Astronomical Center, Department of Astrophysics,ul. Rabianska 8, 87-100 Torun, Poland5 SOFIA-USRA, NASA Ames Research Center, Moffett Field, CA 94035, USA6 Deutsches SOFIA Institut, Universitat Stuttgart, 70569 Stuttgart, Germany

E-mail contact: rgrellma at eso.org

The characterization of multiple stellar systems is an important ingredient for testing current star formation models.

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Stars are more often found in multiple systems, the more massive they are. A complete knowledge of the multiplicityof high-mass stars over the full range of orbit separations is thus essential to understand their still debated formationprocess. Infrared long baseline interferometry is very well suited to close the gap between spectroscopic and adaptiveoptics searches. Observations of the Orion Nebula Cluster in general and the Trapezium Cluster in particular canhelp to answer the question about the origin and evolution of multiple stars. Earlier studies provide a good knowledgeabout the multiplicity of the stars at very small (spectroscopic companions) and large separations (AO, specklecompanions) and thus make the ONC a good target for such a project. We used the near infrared interferometricinstrument AMBER at ESOs Very Large Telescope Interferometer to observe a sample of bright stars in the ONC. Wecomplement our data set by archival NACO observations of θ1 Ori A to obtain more information about the orbit ofthe close visual companion. Our observations resolve the known multiple systems θ1 Ori C and θ1 Ori A and providenew orbit points, which confirm the predicted orbit and the determined stellar parameters for θ1 Ori C. CombiningAMBER and NACO data for θ1 Ori A we were able to follow the (orbital) motion of the companion from 2003 to2011. We furthermore find hints for a companion around θ1 Ori D, whose existence has been suggested already before,and a previously unknown companion to NU Ori. With a probability of ∼ 90% we can exclude further companionswith masses of ≥ 3M⊙ around our sample stars for separations between ∼ 2mas and ∼ 110mas. We conclude thatthe companion around θ1 Ori A is most likely physically related to the primary star and not only a chance projectedstar. The newly discovered possible companions further increase the multiplicity in the ONC. For our sample of twoO and three B-type stars we find on average 2.5 known companions per primary, which is around five times more thanfor low-mass stars.

Accepted by A&A


Maps of Massive Clumps in the Early Stage of Cluster Formation: Two Modes of ClusterFormation, Coeval or Non-Coeval?

Aya E. Higuchi1,2, Yasutaka Kurono2, Takahiro Naoi2, Masao Saito1,2, Rainer Mauersberger1 andRyohei Kawabe1,2

1 Joint ALMA Observatory, Alonso de C’ordova 3107, Vitacura, Santiago, Chile2 National Astronomical Observatory of Japan 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan

E-mail contact: ahiguchi at alma.cl

We present maps of 7 young massive molecular clumps within 5 target regions in the C18O (J=1–0) line emission, usingthe Nobeyama 45m telescope. These clumps, which are not associated with clusters, lie at distances between 0.7 to2.1 kpc. We find C18O clumps with radii of 0.5–1.7 pc, masses of 470–4200M⊙, and velocity widths of 1.4–3.3 km s−1.All of the clumps are massive and approximately in virial equilibrium, suggesting they will potentially form clusters.Three of our target regions are associated with H ii regions (”CWHRs” from Clump with H ii Regions), and the othertwo are without H ii regions (CWOHRs). The C18O clumps can be classified into two morphological types: CWHRsshape a filamentary or shell-like structure, CWOHRs are spherical. The two CWOHRs have systematic velocitygradients. Using the publicly released WISE database, Class I and Class II protostellar candidates were identifiedwithin the C18O clumps. The fraction of the Class I candidates among all YSO candidates (Class I+Class II) is ≥

50% in CWHRs, and ≤ 50% in CWOHRs. We conclude that effects from the H ii regions can be seen in (1) spatialdistributions of the clumps: filamentary or shell-like structure running along the H ii regions, (2) velocity structuresof the clumps: large velocity dispersion along shells, and (3) small age spreads of YSOs. The small spread in age ofthe YSOs show that the presence of H ii regions tend to trigger coeval cluster formation.

Accepted by ApJ


Populations of Young Stellar Objects in Nearby Molecular Clouds

Tien-Hao Hsieh1 and Shih-Ping Lai1

1 National Tsing Hua University, Taiwan

E-mail contact: shawinchone at gmail.com

We develop a new method to identify YSOs from star-forming regions using the photometry data from Spitzer’s

25

c2d Legacy Project. The aim is to obtain YSO lists as complete as possible for studying the statistical properties,such as Star Formation Rate (SFR) and lifetimes of YSOs in different evolutionary stages. The largest obstacle foridentifying YSOs comes from background galaxies with similar SEDs to YSOs. Traditionally, selected color-colorand color-magnitude criteria are used to separate YSOs and galaxies. However, since there is no obvious boundarybetween YSOs and galaxies in Color-Color Diagrams (CCDs) and Color-Magnitude Diagrams (CMDs), those criteriamay exclude faint YSOs near the boundary. In this paper, we separate the YSOs and galaxies in multi-dimensional(Multi-D) magnitude space, which is equivalent to using all variations of CMDs simultaneously. Comparing sourcesfrom molecular clouds to Spitzer’s SWIRE data, which have negligible amount of YSOs, we can naturally identify YSOcandidates locating outside of the galaxy populated regions in the Multi-D space. In the five c2d-surveyed clouds, weselect 322 new YSO candidates (YSOc), miss/exclude 33 YSOc compared to Evans et al. 2009 and result in 1313 YSOcin total. As a result, SFR increases 28% correspondingly, but the lifetimes of YSOs in different evolutionary stagesremain unchanged. Comparing to theories Krumholz & McKee 2005, our derived SFR suggests that star formation inlarge scale is dominated by supersonic turbulence rather than magnetic fields. Furthermore, we identify 7 new VeryLow Luminosity Objects.

Accepted by ApJ


A hybrid SPH/N-body method for star cluster simulations

David A. Hubber1,2, Richard J. Allison1,3, Rory Smith4 and Simon P. Goodwin1

1 Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH,UK2 School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK3 Zentrum fur Astronomie der Universitat Heidelberg, Institut fur Theoretische Astrophysik, Germany4 Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion, Chile

E-mail contact: d.hubber at sheffield.ac.uk

We present a new hybrid Smoothed Particle Hydrodynamics (SPH)/N -body method for modelling the collisionalstellar dynamics of young clusters in a live gas background. By deriving the equations of motion from Lagrangianmechanics we obtain a formally conservative combined SPH-N -body scheme. The SPH gas particles are integratedwith a 2nd order Leapfrog, and the stars with a 4th order Hermite scheme. Our new approach is intended to bridgethe divide between the detailed, but expensive, full hydrodynamical simulations of star formation, and pure N -bodysimulations of gas-free star clusters. We have implemented this hybrid approach in the SPH code SEREN (Hubberet al. 2011) and perform a series of simple tests to demonstrate the fidelity of the algorithm and its conservationproperties. We investigate and present resolution criteria to adequately resolve the density field and to prevent strongnumerical scattering effects. Future developments will include a more sophisticated treatment of binaries.

Accepted by MNRAS


An improved sink particle algorithm for SPH simulations

David A. Hubber1,2, Stefanie Walch3,4 and Anthony P. Whitworth3

1 Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH,UK2 School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK3 School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, CF24 3AA, UK4 Max-Planck-Institut fur Astrophysik, Karl-Schwarzschild-Str. 1, Garching, D84758, Germany

E-mail contact: d.hubber at sheffield.ac.uk

Numerical simulations of star formation frequently rely on the implementation of sink particles, (a) to avoid expendingcomputational resource on the detailed internal physics of individual collapsing protostars, (b) to derive mass functions,binary statistics and clustering kinematics (and hence to make comparisons with observation), and (c) to modelradiative and mechanical feedback; sink particles are also used in other contexts, for example to represent accreting

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black holes in galactic nuclei. We present a new algorithm for creating and evolving sink particles in SPH simulations,which appears to represent a significant improvement over existing algorithms – particularly in situations where sinksare introduced after the gas has become optically thick to its own cooling radiation and started to heat up by adiabaticcompression. (i) It avoids spurious creation of sinks. (ii) It regulates the accretion of matter onto a sink so as tomitigate non-physical perturbations in the vicinity of the sink. (iii) Sinks accrete matter, but the associated angularmomentum is transferred back to the surrounding medium. With the new algorithm – and modulo the need to invokesufficient resolution to capture the physics preceding sink formation – the properties of sinks formed in simulationsare essentially independent of the user-defined parameters of sink creation, or the number of SPH particles used.

Accepted by MNRAS


The mass of the black hole in GRS 1915+105: new constraints from IR spectroscopy

D. J. Hurley1, P. J. Callanan1, P. Elebert1 and M. T. Reynolds2

1 Department of Physics, University College Cork, Cork, Ireland2 Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48109, USA

E-mail contact: d.j.hurley at mars.ucc.ie

GRS 1915+105 has the largest mass function of any Galactic black hole system, although the error is relatively large.Here we present spectroscopic analysis of medium-resolution IR VLT archival data of GRS 1915+105 in the K-band.We find an updated ephemeris, and report on attempts to improve the mass function by a refinement of the radialvelocity estimate. We show that the spectra are significantly affected by the presence of phase-dependent CO bandheademission, possibly originating from the accretion disc: we discuss the impact this has on efforts to better constrainthe black hole mass. We report on a possible way to measure the radial velocity utilising apparent H-band atomicabsorption features and also discuss the general uncertainty of the system parameters of this well-studied object.

Accepted by MNRAS


On vertical variations of gas flow in protoplanetary disks and their impact on the trans-port of solids

Emmanuel Jacquet

Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St Georges Street, Toronto, ON M5S 3H8,Canada

E-mail contact: ejacquet at cita.utoronto.ca

A major uncertainty in accretion disk theory is the nature and properties of gas turbulence, which drives transport inprotoplanetary disks. The commonly used viscous prescription for the Maxwell-Reynolds stress tensor gives rise to ameridional circulation where flow is outward near the midplane and inward away from it. This meridional circulationhas been proposed as an explanation for the presence of high-temperature minerals (believed to be of inner solarsystem provenance) in comets. However, it has not been observed in simulations of magnetohydrodynamical (MHD)turbulence so far. In this study, we evaluate the extent to which the net transport of solids can be diagnostic of theexistence of meridional circulation. To that end, we propose and motivate a prescription for MHD turbulence whichhas the same free parameters as the viscous one. We compare the effects of both prescriptions on the radial transportof small solid particles and find that their net, vertically integrated radial flux is actually quite insensitive to the flowstructure for a given vertical average of the turbulence parameter α, which we explain. Given current uncertaintieson disk turbulence, one-dimensional models are thus most appropriate to investigate radial transport of solids. Acorollary is that the presence of high-temperature material in comets cannot be considered an unequivocal diagnosticof meridional circulation. In fact, we argue that outward transport in viscous disk models is more properly attributedto turbulent diffusion rather than to the mean flows of the gas.

Accepted by A&A


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Water transport in protoplanetary disks and the hydrogen isotopic composition of chon-drites

Emmanuel Jacquet1,2 and Francois Robert2

1 Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St Georges Street, Toronto, ON M5S3H8, Canada2 Laboratoire de Mineralogie et de Cosmochimie du Museum, CNRS & Museum National d’Histoire Naturelle, UMR7202, 57 rue Cuvier, 75005 Paris, France

E-mail contact: ejacquet at cita.utoronto.ca

The D/H ratios of carbonaceous chondrites, believed to reflect that of water in the inner early solar system, areintermediate between the protosolar value and that of most comets. The isotopic composition of cometary water hasbeen accounted for by several models where the isotopic composition of water vapor evolved by isotopic exchange withhydrogen gas in the protoplanetary disk. However, the position and the wide variations of the distribution of D/Hratios in carbonaceous chondrites have yet to be explained. In this paper, we assume that the D/H composition ofcometary ice was achieved in the disk building phase and model the further isotopic evolution of water in the innerdisk in the classical T Tauri stage. Reaction kinetics compel isotopic exchange between water and hydrogen gas tostop at ∼500 K, but equilibrated water can be transported to the snow line (and beyond) via turbulent diffusion andconsequently mix with isotopically comet-like water. Under certain simplifying assumptions, we calculate analyticallythis mixing and the resulting probability distribution function of the D/H ratio of ice accreted in planetesimals andcompare it with observational data. The distribution essentially depends on two parameters: the radial Schmidtnumber ScR, which ratios the efficiencies of angular momentum transport and turbulent diffusion, and the range ofheliocentric distances of accretion sampled by chondrites. The minimum D/H ratio of the distribution correspondsto the composition of water condensed at the snow line, which is primarily set by ScR. Observations constrain thelatter to low values (0.1-0.3), which suggests that turbulence in the planet-forming region was hydrodynamical innature, as would be expected in a dead zone. Such efficient outward diffusion would also account for the presence ofhigh-temperature minerals in comets.

Accepted by Icarus


AFGL 5157 NH3: A new stellar cluster in the forming

Zhibo Jiang1,2, Zhiwei Chen1,2,3, Yuan Wang1,2, Ji Yang1, Jiasheng Huang4, Qizhou Zhang4, and GiovaniFazio4

1 Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijign Road, Nanjing 210008, China2 Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, China3 Graduate School, Chinese Academy of Sciences, China4 Harvard-Smithsonian Center for Astrophysics,60 Garden Street,Cambridge, MA 02138, USA

E-mail contact: zbjiang at pmo.ac.cn

We present the analysis of Spitzer/IRAC and NIR imaging observation of AFGL 5157, an active star forming region.In the IRAC images, this region shows strong PAH emissions in channel 4 and H2 emissions in channel 2. Many ofthe H2 features are aligned to form jet-like structures. Three bipolar jets in the NH3 core region and a couple of jetsnorthwest of the core have been identified. We identify the possible driving agents of the bipolar jets and show themto be very young. An embedded cluster has been detected in the NH3 core; many members in the cluster show theirSEDs increasing from JHK bands toward longer wavelength, indicative of their early evolutionary stages. Millimeterand sub-millimeter continuum emissions are found to coincide spatially with these presumable Class 0/I sources, inthe NH3 core and the NW subregion. The existence of H2 bipolar jets and very young stellar objects suggests thatstar formation is still going on at present epoch in these subregions. Combining the information from previous studies,we propose a sequential star formation scenario in the whole AFGL 5157 region.

Accepted by Research in Astronomy and Astrophysics


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Continuum Variability of Deeply Embedded Protostars as a Probe of Envelope Structure

Doug Johnstone1,2,3, Benjamin Hendricks3,4, Gregory J. Herczeg5 and Simon Bruderer6

1 Joint Astronomy Centre, 660 North Aohoku Place, University Park, Hilo, HI 96720, USA2 National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Rd, Victoria, BC, V9E2E7, Canada3 Department of Physics & Astronomy, University of Victoria, Victoria, BC, V8P 1A1, Canada4 Zentrum fur Astronomie der Universitat Heidelberg, Landessternwarte, Konigstuhl 12, D-69117 Heidelberg, Germany5 Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, HaiDian Qu, Beijing, P.R.China6 Max-Planck-Institut fur extraterrestriche Physik, Giessenbachstrasse 1, 85748, Garching, Germany

E-mail contact: doug.johnstone at nrc-cnrc.gc.ca

Stars may be assembled in large growth spurts, however the evidence for this hypothesis is circumstantial. Directlystudying the accretion at the earliest phases of stellar growth is challenging because young stars are deeply embeddedin optically thick envelopes, which have spectral energy distributions that peak in the far-IR, where observationsare difficult. In this paper, we consider the feasibility of detecting accretion outbursts from these younger stars byinvestigating the timescales for how the protostellar envelope responds to changes in the emission properties of thecentral source. The envelope heats up in response to an outburst, brightening at all wavelengths and with the emissionpeak moving to shorter wavelengths. The timescale for this change depends on the time for dust grains to heat andre-emit photons and the time required for the energy to escape the inner, optically-thick portion of the envelope. Wefind that the dust response time is much shorter than the photon propagation time and thus the timescale over whichthe emission varies is set by time delays imposed by geometry. These times are hours to days near the peak of thespectral energy distribution and weeks to months in the sub-mm. The ideal location to quickly detect continuumvariability is therefore in the mid- to far-IR, near the peak of the spectral energy distribution, where the change inemission amplitude is largest. Searching for variability in sub-mm continuum emission is also feasible, though with alonger time separation and a weaker relationship between the amount of detected emission amplitude and change incentral source luminosity. Such observations would constrain accretion histories of protostars and would help to tracethe disk/envelope instabilities that lead to stellar growth.

Accepted by ApJ


Herschel-HIFI observations of high-J CO and isotopologues in star-forming regions:from low- to high-mass

I. San Jose-Garcıa1, J. C. Mottram1, L. E. Kristensen14, E. F. van Dishoeck1,2, U. A. Yιldιz1, F. F. S.van der Tak3,4, F. Herpin5,6, R. Visser7, C. Mc Coey8, F. Wyrowski9, J. Braine5,6, and D. Johnstone10,11

1 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands2 Max Planck Institut fur Extraterrestrische Physik, Giessenbachstrasse 2, 85478 Garching, Germany3 SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands4 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands5 Universite de Bordeaux, Observatoire Aquitain des Sciences de l’Univers, 2 rue de l’Observatoire, BP 89, F-33270Floirac Cedex, France6 CNRS, LAB, UMR 5804, Laboratoire d’Astrophysique de Bordeaux, 2 rue de l’Observatoire, BP 89, F-33270 FloiracCedex, France7 Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA8 University of Waterloo, Department of Physics and Astronomy, Waterloo, Ontario, Canada9 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany10 National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BCV9E 2E7, Canada11 Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada

E-mail contact: sanjose at strw.leidenuniv.nl

Context. Our understanding of the star formation process has traditionally been confined to certain mass or luminosity

29

boundaries because most studies focus only on low-, intermediate- or high-mass star-forming regions. As part of the”Water In Star-forming regions with Herschel” (WISH) key program, water and other important molecules, such asCO and OH, have been observed in 51 embedded young stellar objects (YSOs). The studied sample covers a range ofluminosities from <1 to >105 L⊙.Aims. We analyse the CO line emission towards a large sample of protostars in terms of both line intensities andprofiles.Methods. Herschel-HIFI spectra of the 12CO 10-9, 13CO 10-9 and C18O 5-4, 9-8 and 10-9 lines are analysed for a sampleof 51 YSOs. In addition, JCMT spectra of 12CO 3-2 and C18O 3-2 extend this analysis to cooler gas components.Results. All observed CO and isotopologue spectra show a strong linear correlation between the logarithms of theline and bolometric luminosities across six orders of magnitude on both axes. This suggests that the high-J CO linesprimarily trace the amount of dense gas associated with YSOs. This relation can be extended to larger (extragalactic)scales. The majority of the detected 12CO line profiles can be decomposed into a broad and a narrow Gaussiancomponent, while the C18O spectra are mainly fitted with a single Gaussian. A broadening of the line profile is alsoobserved from pre-stellar cores to embedded protostars, which is due mostly to non-thermal motions (turbulence/infall).The widths of the broad 12CO 3-2 and 10-9 velocity components correlate with those of the narrow C18O 9-8 profiles,suggesting that the entrained outflowing gas and envelope motions are related independent of the mass of the protostar.These results indicate that physical processes in protostellar envelopes have similar characteristics across the studiedluminosity range.

Accepted by A&A


Water in star forming regions with Herschel (WISH) III. Far-infrared cooling lines inlow-mass young stellar objects

A. Karska1,2, G.J. Herczeg1,3, E.F. van Dishoeck1,2, S.F. Wampfler4,5, L.E. Kristensen2, J.R. Goicoechea6,R. Visser7, B. Nisini8, I. San Jose-Garcıa2, S. Bruderer1, P. Sniady11,12, S. Doty13, D. Fedele1, U.A. Yıldız2,A.O. Benz4, E. Bergin7, P. Caselli9,10, F. Herpin14,15, M.R. Hogerheijde2, D. Johnstone16,17, J.K. Jørgensen5,R. Liseau18, M. Tafalla19, F. van der Tak20,21, and F. Wyrowski22

1 Max-Planck Institut fur Extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748 Garching, Germany2 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands3 Kavli Institut for Astronomy and Astrophysics, Yi He Yuan Lu 5, HaiDian Qu, Peking University, Beijing, 100871,PR China4 Institute of Astronomy, ETH Zurich, 8093 Zurich, Switzerland5 Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, ØsterVoldgade 5-7, DK-1350 Copenhagen K., Denmark6 Centro de Astrobiologıa. Departamento de Astrofısica. CSIC-INTA. Carretera de Ajalvir, Km 4, Torrejon de Ardoz.28850, Madrid, Spain7 Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA8 INAF - Osservatorio Astronomico di Roma, 00040 Monte Porzio catone, Italy9 School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK10 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy11 Institute of Mathematics, Polish Academy of Sciences, ul. Sniadeckich 8, 00-956 Warszawa, Poland12 Institute of Mathematics, University of Wroclaw, pl. Grunwaldzki 2/4, 50-384 Wroclaw, Poland13 Department of Physics and Astronomy, Denison University, Granville, OH, 43023, USA14 Universite de Bordeaux, Observatoire Aquitain des Sciences de l’Univers, 2 rue de l’Observatoire, BP 89, F-33271Floirac Cedex, France15 CNRS, LAB, UMR 5804, F-33271 Floirac Cedex, France16 National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E2E7, Canada17 Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada18 Department of Radio and Space Science, Chalmers University of Technology, Onsala Space Observatory, 439 92Onsala, Sweden19 Observatorio Astronomico Nacional (IGN), Calle Alfonso XII,3. 28014, Madrid, Spain

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20 SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands21 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands22 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany

E-mail contact: karska at mpe.mpg.de

Context: Understanding the physical phenomena involved in the earlierst stages of protostellar evolution requiresknowledge of the heating and cooling processes that occur in the surroundings of a young stellar object. Spatiallyresolved information from its constituent gas and dust provides the necessary constraints to distinguish betweendifferent theories of accretion energy dissipation into the envelope.Aims: Our aims are to quantify the far-infrared line emission from low-mass protostars and the contribution ofdifferent atomic and molecular species to the gas cooling budget, to determine the spatial extent of the emissionand to investigate the underlying excitation conditions. Analysis of the line cooling will help us to characterize theevolution of the relevant physical processes as the protostar ages.Methods: Far-infrared Herschel-PACS spectra of 18 low-mass protostars of various luminosities and evolutionary stagesare studied in the context of the WISH key program. For most targets, the spectra include many wavelength intervalsselected to cover specific CO, H2O, OH and atomic lines. For four targets the spectra span the entire 55-200 µmregion. The PACS field-of-view covers ∼ 47′′ with the resolution of 9.4′′.Results: Most of the protostars in our sample show strong atomic and molecular far-infrared emission. Water isdetected in 17 out of 18 objects (except TMC1A), including 5 Class I sources. The high-excitation H2O 818–707 63.3µm line (Eu/kB = 1071 K) is detected in 7 sources. CO transitions from J = 14 − 13 up to J = 49 − 48 are foundand show two distinct temperature components on Boltzmann diagrams with rotational temperatures of ∼350 K and∼700 K. H2O has typical excitation temperatures of ∼150 K. Emission from both Class 0 and I sources is usuallyspatially extended along the outflow direction but with a pattern depending on the species and the transition. In theextended sources, emission is stronger off source and extended over ≥10,000 AU scales; in the compact sample, morethan half of the flux originates within 1000 AU of the protostar. The H2O line fluxes correlate strongly with those ofthe high−J CO lines, both for the full array and for the central position, as well as with the bolometric luminosityand envelope mass. They correlate less strongly with OH fluxes and not with [Oi] fluxes. In contrast, [Oi] and OHoften peak together at the central position.Conclusions: The PACS data probe at least two physical components. The H2O and CO emission likely arises innon-dissociative (irradiated) shocks along the outflow walls with a range of pre-shock densities. Some OH is alsoassociated with this component, likely resulting from H2O photodissociation. UV-heated gas contributes only a minorfraction to the CO emission observed by PACS, based on the strong correlation between the shock-dominated CO24-23 line and the CO 14-13 line. [Oi] and some of the OH emission probe dissociative shocks in the inner envelope.The total far-infrared cooling is dominated by H2O and CO, with the fraction contributed by [Oi] increasing for ClassI sources. Consistent with previous studies, the ratio of total far-infrared line emission over bolometric luminositydecreases with evolutionary state.

Accepted by Astronomy & Astrophysics.


The Galactic Center Cloud G0.253+0.016: A Massive Dense Cloud with low Star For-mation Potential

Jens Kauffmann1 and Thushara Pillai1

1 California Institute of Technology, Astronomy Department, 1200 East California Blvd., Pasadena, CA 91125, USA

E-mail contact: jens.kauffmann at astro.caltech.edu

We present the first interferometric molecular line and dust emission maps for the Galactic Center (GC) cloudG0.253+0.016, observed using the Combined Array for Research in Millimeter–wave Astronomy (CARMA) and theSubmillimeter Array (SMA). This cloud is very dense, and concentrates a mass exceeding the Orion Molecular CloudComplex (2 × 105 M⊙) into a radius of only 3pc, but it is essentially starless. G0.253+0.016 therefore violates ”starformation laws” presently used to explain trends in galactic and extragalactic star formation by a factor ∼45. Ourobservations show a lack of dense cores of significant mass and density, thus explaining the low star formation activity.Instead, cores with low densities and line widths 1 km s1−—probably the narrowest lines reported for the GC regionto date—are found. Evolution over several 105 yr is needed before more massive cores, and possibly an Arches–like

31

stellar cluster, could form. Given the disruptive dynamics of the GC region, and the potentially unbound nature ofG0.253+0.016, it is not clear that this evolution will happen.

Accepted by ApJL


Massive Star Formation at the Periphery of the Evolved Giant HII Region W 39

C. R. Kerton1, K. Arvidsson2, and M. J. Alexander3

1 Department of Physics & Astronomy, Iowa State University, Ames, IA 50011, USA2 Astronomy Department, Adler Planetarium, 1300 S. Lake Shore Drive, Chicago, IL 60605, USA3 Department of Physics & Astronomy, University of Wyoming, 1000 E. University, Laramie, WY 82071, USA

E-mail contact: kerton at iastate.edu

We present the first detailed study of the large, ∼30 pc diameter, inner-Galaxy HII region W 39. Radio recombinationline observations combined with HI absorption spectra and Galactic rotation models show that the region lies at V(LSR)= +65.4±0.5 km s−1 corresponding to a near kinematic distance of 4.5±0.2 kpc. Analysis of radio continuum emissionshows that the HII region is being powered by a cluster of OB stars with a combined hydrogen-ionizing luminosity oflog(Q) ≥ 50, and that there are three compact HII regions located on the periphery of W 39, each with log(Q) ∼ 48.5(single O7 - O9 V star equivalent). In the infrared, W 39 has a hierarchical bubble morphology, and is a likely site ofsequential star formation involving massive stars. Kinematic models of the expansion of W 39 yield timescales of orderMyr consistent with a scenario where the formation of the smaller HII regions has been triggered by the expansion ofW 39. Using Spitzer GLIMPSE and MIPSGAL data we show that star-formation activity is not distributed uniformlyaround the periphery of W 39 but is concentrated in two areas that include the compact HII regions as well as anumber of intermediate-mass Class I and Class II YSOs.

Accepted by AJ


Filamentary Accretion Flows in the Embedded Serpens South Protocluster

Helen Kirk1,2, Philip C. Myers1, Tyler L. Bourke1, Robert A. Gutermuth3, Abigail Hedden4 and GrantW. Wilson3

1 Radio & Geoastronomy Division, Harvard Smithsonian Center for Astrophysics, USA2 currently a Banting Fellow at the Origins Institute, McMaster University, Canada3 Department of Astronomy, University of Massachusetts, Amherst, USA4 Army Research Labs, Maryland, USA

E-mail contact: kirkh at mcmaster.ca

One puzzle in understanding how stars form in clusters is the source of mass – is all of the mass in place before the firststars are born, or is there an extended period when the cluster accretes material which can continuously fuel the starformation process? We use a multi-line spectral survey of the southern filament associated with the Serpens Southembedded cluster-forming region in order to determine if mass is accreting from the filament onto the cluster, andwhether the accretion rate is significant. Our analysis suggests that material is flowing along the filament’s long axisat a rate of ∼ 30 M⊙ Myr−1 (inferred from the N2H

+ velocity gradient along the filament), and radially contractingonto the filament at ∼ 130 M⊙ Myr−1 (inferred from HNC self-absorption). These accretion rates are sufficient tosupply mass to the central cluster at a similar rate to the current star formation rate in the cluster. Filamentaryaccretion flows may therefore be very important in the ongoing evolution of this cluster.

Accepted by the Astrophysical Journal


Stellar Populations in the Central 0.5 pc of the Galaxy II: The Initial Mass Function

Jessica R. Lu1, Tuan Do2, Andrea M. Ghez3, Mark R. Morris3, Sylvana Yelda3 and Keith Matthews4

1 Institute for Astronomy, University of Hawaii, USA

32

2 University of California, Irvine, USA3 University of California, Los Angeles, USA4 California Institute of Technology, USA

E-mail contact: jlu at ifa.hawaii.edu

The supermassive black hole at the center of the Milky Way plays host to a massive, young cluster that may haveformed in one of the most inhospitable environments in the Galaxy. We present new measurements of the globalproperties of this cluster, including the initial mass function (IMF), age, and cluster mass. These results are basedon Keck laser-guide-star adaptive optics observations used to identify the young stars and measure their Kp-bandluminosity function as presented in Do et al. 2013. A Bayesian inference methodology is developed to simultaneouslyfit the global properties of the cluster utilizing the observations and extensive simulations of synthetic star clusters.We find that the slope of the mass function for this cluster is α = 1.7± 0.2, which is steeper than previously reported,but still flatter than the traditional Salpeter slope of 2.35. The age of the cluster is between 2.5-5.8 Myr with 95%confidence, which is a younger age than typically adopted but consistent within the uncertainties of past measurements.The exact age of the cluster is difficult to determine since our results show two distinct age solutions (3.9 Myr and 2.8Myr) due to model degeneracies in the relative number of Wolf-Rayet and OB stars. The total cluster mass is between14,000 - 37,000 M⊙ above 1 M⊙ and it is necessary to include multiple star systems in order to fit the observedluminosity function and the number of observed Wolf-Rayet stars. The new IMF slope measurement is now consistentwith X-ray observations indicating a factor of 10 fewer X-ray emitting pre-main-sequence stars than expected whencompared with a Salpeter IMF. The young cluster at the Galactic center is one of the few definitive examples of anIMF that deviates significantly from the near-universal IMFs found in the solar neighborhood.

Accepted by ApJ


A spectroscopic investigation of the O-type star population in four Cygnus OB associ-ations. I. Determination of the binary fraction

L. Mahy1, G. Rauw1, M. De Becker1, P. Eenens2, and C. A. Flores2

1 Institut d’Astrophysique et de Geophysique, Universite de Liege, Bat. B5C, Allee du 6 Aout 17, B-4000, Liege,Belgium2 Departamento de Astronomıa, Universidad de Guanajuato, Apartado 144, 36000 Guanajuato, GTO, Mexico

E-mail contact: mahy at astro.ulg.ac.be

Context. Establishing the multiplicity of O-type stars is the first step towards accurately determining their stellarparameters. Moreover, the distribution of the orbital parameters provides observational clues to the way that O-typestars form and to the interactions during their evolution.Aims. Our objective is to constrain the multiplicity of a sample of O-type stars belonging to poorly investigated OBassociations in the Cygnus complex and for the first time to provide orbital parameters for binaries identified in oursample. Such information is relevant to addressing the issue of the binarity in the context of O-type star formationscenarios.Methods. We performed a long-term spectroscopic survey of nineteen O-type stars. We searched for radial velocityvariations to unveil binaries on timescales from a few days up to a few years, on the basis of a large set of opticalspectra.Results. We confirm the binarity for four objects: HD 193443, HD 228989, HD 229234 and HD 194649. We derive forthe first time the orbital solutions of three systems, and we confirm the values of the fourth, showing that these foursystems all have orbital periods shorter than 10 days. Besides these results, we also detect several objects that shownon-periodic line profile variations in some of their spectral lines. These variations mainly occur in the spectral lines,that are generally affected by the stellar wind and are not likely to be related to binarity.Conclusions. The minimal binary fraction in our sample is estimated to be 21%, but it varies from one OB associationto the next. Indeed, 3 O stars of our sample out of 9 (33%) belonging to Cyg OB1 are binary systems, 0% (0 out of4) in Cyg OB3, 0% (0 out of 3) in Cyg OB8, and 33% (1 out of 3) in Cyg OB9. Our spectroscopic investigation alsostresses the absence of long-period systems among the stars in our sample. This result contrasts with the case of theO-type stellar population in NGC 2244 among which no object showed radial velocity variations on short timescales.However, we show that it is probably an effect of the sample and that this difference does not a priori suggest a

33

somewhat different star forming process in these two environments.

Accepted by A&A


X-Shooter spectroscopy of young stellar objects: II. Impact of chromospheric emissionon accretion rate estimates

C.F. Manara1, L. Testi1,2, E. Rigliaco3, J.M. Alcala4, A. Natta2,5, B. Stelzer6, K. Biazzo4, E. Covino4,S. Covino7, G. Cupani8, V. D’Elia9 and S. Randich2

1 European Southern Observatory, Karl Schwarzschild Str. 2, 85748 Garching, Germany2 INAF - Osservatorio Astrofisico di Arcetri, Largo E.Fermi 5, I-50125 Firenze, Italy3 Department of Planetary Science, Lunar and Planetary Lab, University of Arizona, 1629, E. University Blvd, 85719,Tucson, AZ4 INAF - Osservatorio Astronomico di Capodimonte, Via Moiariello 16, I-80131 Napoli, Italy5 School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland6 INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134 Palermo, Italy7 INAF - Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate (LC), Italy8 INAF - Osservatorio Astronomico di Trieste, via Tiepolo 11, I-34143 Trieste, Italy9 INAF - Osservatorio Astronomico di Roma, Via di Frascati 33, I-00040 Monte Porzio Catone (RM), Italy

E-mail contact: cmanara at eso.org

Context: The lack of knowledge of photospheric parameters and the level of chromospheric activity in young low-masspre-main sequence stars introduces uncertainties when measuring mass accretion rates in accreting (Class II) YoungStellar Objects. A detailed investigation of the effect of chromospheric emission on the estimates of mass accretionrate in young low-mass stars is still missing. This can be undertaken using samples of young diskless (Class III) Kand M-type stars.Aims: Our goal is to measure the chromospheric activity of Class III pre main sequence stars to determine its effecton the estimates of accretion luminosity (Lacc) and mass accretion rate (Macc) in young stellar objects with disks.Method: Using VLT/X-Shooter spectra we have analyzed a sample of 24 non-accreting young stellar objects of spectraltype between K5 and M9.5. We identify the main emission lines normally used as tracers of accretion in Class II objects,and we determine their fluxes in order to estimate the contribution of the chromospheric activity to the line luminosity.Results: We have used the relationships between line luminosity and accretion luminosity derived in the literature forClass II objects to evaluate the impact of chromospheric activity on the accretion rate measurements. We find thatthe typical chromospheric activity would bias the derived accretion luminosity by Lacc,noise < 10−3L⊙, with a strong

dependence with the Teff of the objects. The noise on Macc depends on stellar mass and age, and the typical valuesof log(Macc,noise) range between ∼ −9.2 to −11.6 M⊙/yr.Conclusions: Values of Lacc < 10−3L⊙ obtained in accreting low-mass pre main sequence stars through line luminosityshould be treated with caution as the line emission may be dominated by the contribution of chromospheric activity.

Accepted by Astronomy & Astrophysics


Impact of metallicity on the evolution of young star clusters

M. Mapelli1 and A. Bressan2

1 INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I35122, Padova, Italy2 Scuola Internazionale Superiore di Studi Avanzati (SISSA), Via Bonomea 265, I34136, Trieste, Italy

E-mail contact: michela.mapelli at oapd.inaf.it

We discuss the results of N-body simulations of intermediate-mass young star clusters (SCs) with three different metal-licities (Z = 0.01, 0.1 and 1 Z⊙), including metallicity-dependent stellar evolution recipes and metallicity-dependentprescriptions for stellar winds and remnant formation. The initial half-mass relaxation time of the simulated youngSCs (∼ 10 Myr) is comparable to the lifetime of massive stars. We show that mass-loss by stellar winds influences

34

the reversal of core collapse and the expansion of the half-mass radius. In particular, the post-collapse re-expansionof the core is weaker for metal-poor SCs than for metal-rich SCs, because the former lose less mass (through stellarwinds) than the latter. As a consequence, the half-mass radius expands faster in metal-poor SCs. The difference inthe half-light radius between metal-poor SCs and metal-rich SCs is (up to a factor of two) larger than the differencein the half-mass radius.

Accepted by MNRAS


High angular resolution millimetre continuum observations and modelling of S140-IRS1

Luke T. Maud1, Melvin G. Hoare1, Andy G. Gibb2, Debra Shepherd3,4 and Remy Indebetouw5

1 Department of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK2 Department of Physics and Astronomy, 6224 Agricultural Road, University of British Columbia, Vancouver, BC,V6T 1Z1, Canada3 National Radio Astronomy Observatory, Socorro, NM, 87801, USA4 Square Kilometre Array-Africa, 3rd Floor, The Park, Park Road, Pinelands, 7405, South Africa5 Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325, USA

E-mail contact: phy5lm at leeds.ac.uk

We present high resolution 1.3 millimetre continuum observations of the massive young stellar object S140-IRS1. S140-IRS1 is a disc wind prototype with elongated radio emission (PA ∼ 45◦) perpendicular to the large scale CO outflowin the region. The observations taken with the CARMA B array and the SMA compact configuration correspond toa spatial resolution of 0.3 and 3.0 arcsec respectively. Complementary 2.7 and 3.5 mm data taken with OVRO in acompact configuration are also discussed. The deconvolved position angle for S140-IRS1 of 37◦±15 is compatible witha disc perpendicular to the main CO outflow and NIR monopolar reflection nebula. We have utilised 2D axi-symmetricradiative transfer modelling to interpret the millimetre wave emission from S140-IRS1. The model required the additionof a disc component, as the observed image, flux and visibilities cannot be represented solely by a dusty envelope withpolar cavities. We report that the high resolution image of S140-IRS1 is consistent with the interpretation of emissionfrom a dust disc in a large scale envelope with cleared bipolar cavities. Strong continuum emission is also detected inboth SMA and OVRO maps from the previously discovered sub-millimetre source S140-SMM1 and from the infraredsource S140-IRS3. Furthermore S140-SMM1 is identified with maser sources whose proper motions are consistent withbeing the source of the outflow with position angle ∼20◦ previously associated by some authors with a second outflowcreated by S140-IRS1. Our findings are consistent with a disc wind interpretation of the radio emission for S140-IRS1rather than that of a jet.

Accepted by MNRAS

http://adsabs.harvard.edu/abs/2013MNRAS.428..609M

A molecular outflow driven by the brown dwarf binary FU Tau

J.-L. Monin1, E. Whelan2, B. Lefloch1, C. Dougados1 and C. Alves de Oliveira3

1 UJF-Grenoble / CNRS-INSU, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble,38041, France2 Institut fur Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Sand 1, Eberhard KarlsUniversitat, 72076 Tubingen, Germany3 European Space Astronomy Centre (ESA), P.O. Box 78, 28691 Villanueva de la Canada, Madrid, Spain

E-mail contact: Jean-Louis.Monin at obs.ujf-grenoble.fr

We report the detection of a molecular outflow driven by the brown dwarf binary FU Tau. Using the IRAM 30 mtelescope we observed the 12CO(2-1) (CO) emission in the vicinity of FU Tau and detected a bipolar outflow byexamining the wings of the CO(2-1) line as we moved away from the source position. An integrated map of the wingemission between 3 kms−1 and 5 kms−1 reveals a blue-shifted lobe at a position of ∼ 20 arcsec from the FU Tausystem and at a position angle of ∼ 20◦. The beam size of the observations is 11 arcsec hence it is not possible todistinguish between the two components of the FU Tau binary. However as optical forbidden emission, a strong tracer

35

of the shocks caused by outflow activity, has been detected in the spectrum of FU Tau A we assume this componentto be the driving source of the molecular outflow.We estimate the mass and mass outflow rate of the outflow at 4 × 10−6 M⊙ and 6 × 10−10 M⊙/yr respectively.These results agree well with previous estimates for BD molecular outflows. FU Tau A is now the third BD found tobe associated with molecular outflow activity and this discovery adds to the already extensive list of the interestingproperties of FU Tau.



Effects of Magnetic Field and FUV Radiation on the Structures of Bright-rimmedClouds

Kazutaka Motoyama1, Tomofumi Umemoto2, and Hsien Shang3,4 and Tatsuhiko Hasegawa3

1 National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo, Japan 101-84302 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, Japan 191-85883 Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan 1064 Theoretical Institute for Advanced Research in Astrophysics,National Tsing Hua University, 101, Sec. 2, Kuang-FuRd., Hsin-Chu, Taiwan 30013

E-mail contact: motoyama at nii.ac.jp

The bright-rimmed cloud SFO 22 was observed with the 45 m telescope of Nobeyama Radio Observatory in the 12CO(J = 1-0), 13CO (J = 1-0), and C18O (J = 1-0) lines, where well-developed head-tail structure and small line widthswere found. Such features were predicted by radiation-driven implosion models, suggesting that SFO 22 may be ina quasi-stationary equilibrium state. We compare the observed properties with those from numerical models of aphoto-evaporating cloud, which include effects of magnetic pressure and heating due to strong far-ultraviolet (FUV)radiation from an exciting star. The magnetic pressure may play a more important role in the density structures ofbright-rimmed clouds, than the thermal pressure that is enhanced by the FUV radiation. The FUV radiation can heatthe cloud surface to near 30 K, however, its effect is not enough to reproduce the observed density structure of SFO22. An initial magnetic field of 5 µG in our numerical models produces the best agreement with the observations, andits direction can affect the structures of bright-rimmed clouds.

Accepted by ApJ


Disentangling the entangled: Observations and analysis of the triple non-coeval proto-stellar system VLA1623

Nadia M. Murillo1 and Shih-Ping Lai1,2

1 Institute of Astronomy and Department of Physics, National Tsing Hua University, 101 Section 2 Kuang Fu Road,Hsinchu 30013, Taiwan2 Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei, 10617, Taiwan

E-mail contact: nmurillo at mpe.mpg.de

Commonplace at every evolutionary stage, Multiple Protostellar Systems (MPSs) are thought to be formed throughfragmentation, but it is unclear when and how. The youngest MPSs, which have not yet undergone much evolution,provide important constraints to this question. It is then of interest to disentangle early stage MPSs. In this letterwe present the results of our work on VLA1623 using our observations and archival data from the SubmillimeterArray (SMA). Our continuum and line observations trace VLA1623’s components, outflow and envelope, revealingunexpected characteristics. We construct the SED for each component using the results of our work and data fromliterature, as well as derive physical parameters from continuum and perform a simple kinematical analysis of thecircumstellar material. Our results show VLA1623 to be a triple non-coeval system composed of VLA1623A, B & W,with each source driving its own outflow and unevenly distributed circumstellar material. From the SED, physicalparameters and IR emission we conclude that VLA1623A & W are Class 0 and I protostars, respectively, and togetherdrive the bulk of the observed outflow. Furthermore, we find two surprising results, first the presence of a rotating

36

disk-like structure about VLA1623A with indications of pure Keplerian rotation, which, if real, would make it one ofthe first evidence of Keplerian disk structures around Class 0 protostars. Second, we find VLA1623B to be a bonafideextremely young protostellar object between the starless core and Class 0 stages.



Pulsed Accretion in a Variable Protostar

James Muzerolle1, Elise Furlan2, Kevin Flaherty3, Zoltan Balog4, Robert Gutermuth5

1 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA2 National Optical Astronomy Observatory, Tucson, AZ, 85719, USA3 Steward Observatory, 933 N. Cherry Ave., The University of Arizona, Tucson, AZ 85721, USA4 Max-Planck-Institut fur Astronomie, Konigstuhl 17, 69117, Heidelberg, Germany5 Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA

E-mail contact: muzerol at stsci.edu

Periodic increases in luminosity arising from variable accretion rates have been predicted for some close pre-mainsequence binary stars as they grow from circumbinary disks. The phenomenon is known as ”pulsed accretion” andcan affect the orbital evolution and mass distribution of young binaries, as well as the potential for planet formationin the circumbinary environment. Accretion variability is a common feature of young stars, with a large range ofamplitudes and timescales as measured from multi-epoch observations at optical and infrared wavelengths. Periodicvariations consistent with pulsed accretion have been seen in only a few young binaries via optical accretion tracers,albeit intermittently with accretion luminosity variations ranging from 0-50 percent from orbit to orbit. Here we reporton a young protostar (age ∼105 yr) that exhibits periodic variability in which the infrared luminosity increases by afactor of 10 in roughly one week every 25.34 days. We attribute this to pulsed accretion associated with an unseenbinary companion. The strength and regularity of this accretion signal is surprising; it may be related to the veryyoung age of the system, which is a factor of ten younger than the other pulsed accretors previously studied.

Accepted by Nature


Origin of the dense core mass function in contracting filaments

Philip C. Myers1

1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA

E-mail contact: pmyers at cfa.harvard.edu

Mass functions of starless dense cores (CMFs) may arise from contraction and dispersal of core-forming filaments.In an illustrative model, a filament contracts radially by self-gravity, increasing the mass of its cores. During thiscontraction, FUV photoevaporation and ablation by shocks and winds disperse filament gas and limit core growth.The stopping times of core growth are described by a waiting-time distribution. The initial filament column densityprofile and the resulting CMF each match recent Herschel observations in detail. Then low-mass cores have shortgrowth ages and arise from the innermost filament gas, while massive cores have long growth ages and draw from moreextended filament gas. The model fits the initial density profile and CMF best for mean core density 2 × 104 cm−3

and filament dispersal time scale 0.5 Myr. Then the typical core mass, radius, mean column density, and contractionspeed are respectively 0.8 solar masses, 0.06 pc, 6 × 1021 cm−2, and 0.07 km s−1, also in accord with observed values.



Discovering young stars in the Gum 31 region with infrared observations

Henrike Ohlendorf1, Thomas Preibisch1, Benjamin Gaczkowski1, Thorsten Ratzka1, Judith Ngoumou1,Veronica Roccatagliata1 and Rebekka Grellmann1

37

1 Universitats-Sternwarte Munchen, Ludwig-Maximilians-Universitat, Scheinerstr. 1, 81679 Munchen, Germany

E-mail contact: ohlendorf at usm.uni-muenchen.de

Context. The Gum31 bubble containing the stellar cluster NGC3324 is a poorly-studied young region close to theCarina Nebula.Aims. We are aiming to characterise the young stellar and protostellar population in and around Gum31 and toinvestigate the star-formation process in this region.Methods. We identify candidate young stellar objects from Spitzer, WISE, and Herschel data. Combining these, weanalyse the spectral energy distributions of the candidate young stellar objects. With density and temperature mapsobtained from Herschel data and comparisons to a ‘collect and collapse’ scenario for the region we are able to furtherconstrain the characteristics of the region as a whole.Results. 661 candidate young stellar objects are found from WISE data, 91 protostar candidates are detected throughHerschel observations in a 1.0◦ × 1.1◦ area. Most of these objects are found in small clusters or are well aligned withthe H II bubble. We also identify the sources of Herbig-Haro jets. The infrared morphology of the region suggests thatit is part of the larger Carina Nebula complex.Conclusions. The location of the candidate young stellar objects in the rim of the H II bubble is suggestive of theirbeing triggered by a ‘collect and collapse’ scenario, which agrees well with the observed parameters of the region.Some candidate young stellar objects are found in the heads of pillars, which points towards radiative triggering ofstar formation. Thus, we find evidence that in the region different mechanisms of triggered star formation are at work.Correcting the number of candidate young stellar objects for contamination we find ∼ 600 young stellar objects inGum31 above our completeness limit of about 1M⊙. Extrapolating the initial mass function down to 0.1M⊙, weestimate a total population of ∼ 5000 young stars for the region.


Preprints can be obtained from http://arxiv.org/pdf/1302.0007

and http://www.usm.uni-muenchen.de/people/preibisch/publications.html (high resolution)

H2CO and N2H+ in Protoplanetary Disks: Evidence for a CO-ice Regulated Chemistry

Chunhua Qi1, Karin I. Oberg2 and David J. Wilner1

1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA2 University of Virginia, Charlottesville, VA 22904, USA

E-mail contact: cqi at cfa.harvard.edu

We present Submillimeter Array observations of H2CO and N2H+ emission in the disks around the T Tauri star

TW Hya and the Herbig Ae star HD 163296 at 2′′–6′′ resolution and discuss the distribution of these speci es withrespect to CO freeze-out. The H2CO and N2H

+ emission toward HD 163296 does not peak at the continuum emissioncenter that marks the stellar position but is instead significantly offset. Using a previously developed model for thephysical structure of this disk, we show that the H2CO observations are reproduced if H2CO is present predominantlyin the cold outer disk regions. A model where H2CO is present only beyond the CO snow line (estimated at a radiusof 160 AU) matches the observations well. We also show that the average H2CO excitation temperature, calculatedfrom two transitions of H2CO observed in these two disks and a larger sample of disks around T Tauri stars in theDISCS (the Disk Imaging Survey of Chemistry with SMA) program, is consistent with the CO freeze-out temperatureof ∼20 K. In addition, we show that N2H

+ and H2CO line fluxes in disks are strongly correlated, indicative of co-formation of these species across the sample. Taken together, these results imply that H2CO and N2H

+ are generallypresent in disks only at low temperatures where CO depletes onto grains, consistent with fast destruction of N2H

+ bygas-phase CO, and in situ formation of H2CO through hydrogenation of CO ice. In this scenario H2CO, CH3OH andN2H

+ emission in disks should appear as rings with the inner edge at the CO midplane snow line. This predictioncan be tested directly using observations from ALMA with higher resolution and better sensitivity.

Accepted by ApJ


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First detection of c-C3H2 in a circumstellar disk

Chunhua Qi1, Karin I. Oberg2, David J. Wilner1 and Katherine A. Rosenfeld1

1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA2 University of Virginia, Charlottesville, VA 22904, USA

E-mail contact: cqi at cfa.harvard.edu

We report the first detection of c-C3H2 in a circumstellar disk. The c-C3H2 J=6−5 line (217.882 GHz) is detected andimaged through Atacama Large Millimeter Array (ALMA) Science Verification observations toward the disk aroundthe Herbig Ae star HD 163296 at 0.8′′ resolution. The emission is consistent with that arising from a Keplerian rotatingdisk. Two additional c-C3H2 transitions are also tentatively detected, bolstering the identification of this species, butwith insufficient signal-to-noise ratio to constrain the spatial distribution. Using a previously developed model for thephysical structure of this disk, we fit a radial power-law distribution model to the c-C3H2 6 − 5 emission and findthat c-C3H2 is present in a ring structure from an inner radius of about 30 AU to an outer radius of about 165 AU.The column density is estimated to be 1012–1013 cm−2. The clear detection and intriguing ring structure suggest thatc-C3H2 has the potential to become a useful probe of radiation penetration in disks.

Accepted by ApJL


CARMA interferometric observations of 2MASS J044427+2512: the first spatially re-solved observations of thermal emission of a brown dwarf disk

L. Ricci1, A. Isella1, J. M. Carpenter1, L. Testi2

1 Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125, USA2 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen, Germany

E-mail contact: silich at inaoep.mx

We present CARMA 1.3 mm continuum data of the disk surrounding the young brown dwarf 2MASS J044427+2512in the Taurus molecular cloud. The high angular resolution of the CARMA observations (0.16′′) allows us to spatiallyresolve for the first time the thermal emission from dust around a brown dwarf. We analyze the interferometricvisibilities and constrain the disk outer radius adopting disk models with power-law radial profiles of the dust surfacedensity. In the case of a power-law index equal to or lower than 1, we obtain a disk radius in the range of about 15- 30 AU, while larger disks are inferred for steeper radial profiles. By combining this information on the disk spatialextent with the sub-mm spectral index of this source we find conclusive evidence for mm-sized grains, or larger, inthis brown dwarf disk. We discuss the implications of our results on the models of dust evolution in proto-planetarydisks and brown dwarf formation.

Accepted by ApJL


Herschel Observations of the W3 GMC: Clues to the Formation of Clusters of High-MassStars

A. Rivera-Ingraham1,2,3, P. G. Martin4, D. Polychroni5, F. Motte6, N. Schneider6,7,8, S. Bontemps7,8, M.Hennemann6, A. Menshchikov6, Q. Nguyen Luong4, Ph. Andre6, D. Arzoumanian6, J.-Ph. Bernard3,J. Di Francesco9,10, D. Elia11, C. Fallschee10,9, T. Hill6, J. Z. Li12, V. Minier6, S. Pezzuto11, A. Roy4,K. L. J. Rygl11, S. I. Sadavoy10,9, L. Spinoglio 11, G. J. White13,14, C. D. Wilson15

1 Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4,Canada2 Universite de Toulouse, UPS-OMP, IRAP, F-31028 Toulouse cedex 4, France3 CNRS, IRAP, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4, France4 Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S3H8, Canada5 Department of Astrophysics, Astronomy and Mechanics, Faculty of Physics, University of Athens, Panepistimiopolis,

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15784 Zografos, Athens, Greece6 Laboratoire AIM, CEA/DSM/Irfu - CNRS/INSU - Universite Paris Diderot, CEA-Saclay, F-91191 Gif-sur-YvetteCedex, France7 Univ. Bordeaux, LAB, UMR 5804, F-33270 Floirac, France8 CNRS, LAB, UMR 5804, F-33270 Floirac, France9 National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E2E7, Canada10 Department of Physics and Astronomy, University of Victoria, PO Box 355, STN CSC, Victoria, BC, V8W 3P6,Canada11 INAF-Istituto di Astrosica e Planetologia Spaziali, via Fosso del Cavaliere 100, I-00133 Rome, Italy12 National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China13 Department of Physical sciences, The Open University, Milton Keynes, UK14 RALspace, The Rutherford Appleton Laboratory, Chilton, Didcot, UK15 Department of Physics and Astronomy, McMaster University, Hamilton, ON, L8S 4M1, Canada

E-mail contact: arivera at irap.omp.eu

The W3 GMC is a prime target for the study of the early stages of high-mass star formation. We have used Herscheldata from the HOBYS key program to produce and analyze column density and temperature maps. Two preliminarycatalogs were produced by extracting sources from the column density map and from Herschel maps convolved tothe 500 micron resolution. Herschel reveals that among the compact sources (FWHM<0.45 pc), W3 East, W3West, and W3 (OH) are the most massive and luminous and have the highest column density. Considering theunique properties of W3 East and W3 West, the only clumps with on-going high-mass star formation, we suggest a’convergent constructive feedback’ scenario to account for the formation of a cluster with decreasing age and increasingsystem/source mass toward the innermost regions. This process, which relies on feedback by high-mass stars to ensurethe availability of material during cluster formation, could also lead to the creation of an environment suitable for theformation of Trapezium-like systems. In common with other scenarios proposed in other HOBYS studies, our resultsindicate that an active/dynamic process aiding in the accumulation, compression, and confinement of material is acritical feature of the high-mass star/cluster formation, distinguishing it from classical low-mass star formation. Theenvironmental conditions and availability of triggers determine the form in which this process occurs, implying thathigh-mass star/cluster formation could arise from a range of scenarios: from large scale convergence of turbulent flows,to convergent constructive feedback or mergers of filaments.

Accepted by ApJ


The spectral type of CHS7797 - an intriguing very low mass periodic variable in theOrion Nebula Cluster

Marıa V. Rodrıguez-Ledesma1,2, Reinhard Mundt1, Olga Pintado3, Steve Boudreault4,5, Frederic Hessman2,and William Herbst6

1 Max-Planck-Institut fur Astronomie (MPIA), Konigstuhl 17, D-69117 Heidelberg, Germany2 Institut fur Astrophysik, Georg-August-Universitat, Friedrich-Hund-Platz 1, D-37077 Gottingen, Germany3 Instituto Superior de Corellacion Geologica, CONICET, Miguel Lillo 205, 4000, San Miguel de Tucuman, Argentina4 Instituto de Astrofısica de Canarias (IAC), Calle Vıa Lactea s/n, E-38200 La Laguna, Tenerife, Spain5 Departamento de Astrofısica, Universidad de La Laguna (ULL), E-38205 La Laguna, Tenerife, Spain6 Astronomy Department, Wesleyan University, Middletown, CT 06459 USA

E-mail contact: vicrodriguez at mpia.de

We present the spectroscopic characterization of the unusual high-amplitude very low mass pre-main-sequence periodicvariable CHS7797. This study is based on optical medium-resolution (R=2200) spectroscopy in the 6450-8600 A range,carried out with GMOS-GEMINI-S in March 2011. Observations of CHS7797 have been carried out at two distinctphases of the 17.8d period, namely at maximum and four days before maximum. Four different spectral indices wereused for the spectral classification at these two phases, all of them well-suited for spectral classification of young andobscured late M dwarfs. In addition, the gravity-sensitive NaI (8183/8195 A) and KI (7665/7699 A) doublet lines wereused to confirm the young age of CHS7797. From the spectrum obtained at maximum light we derived a spectral type

40

(SpT) of M6.05, while for the spectrum taken four days before maximum the derived SpT is M5.75. The derived SpTsconfirm that CHS7797 has a mass in the stellar-substellar boundary mass range. In addition, the small differences inthe derived SpTs at the two observed phases may provide indirect hints that CHS7797 is a binary system of similarmass components surrounded by a tilted circumbinary disk, a system similar to KH15D.

Accepted by A&A


The interplay between X-ray photoevaporation and planet formation

Giovanni Rosotti1,2,3, Barbara Ercolano2,3, James Owen4 and Philip Armitage5,6

1 Max-Planck-Institut fur extraterrestrische Physik, Giessenbachstraße, D-85748 Garching, Germany2 Excellence Cluster Universe, Boltzmannstr. 2, D-85748 Garching, Germany3 Universitats-Sternwarte Munchen, Scheinerstraße 1, D-81679 Munchen, Germany4 Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto M5S 3H8, Canada5 JILA, University of Colorado and NIST, 440 UCB, Boulder, CO 80309-0440, USA6 Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, USA

E-mail contact: rosotti at usm.lmu.de

We assess the potential of planet formation instigating the early formation of a photoevaporation driven gap, up toradii larger than typical for photoevaporation alone. For our investigation we make use of hydrodynamics models ofphotoevaporating discs with a giant planet embedded. We find that, by reducing the mass accretion flow onto the star,discs that form giant planets will be dispersed at earlier times than discs without planets by X-ray photoevaporation.By clearing the portion of the disc inner of the planet orbital radius, planet formation induced photoevaporation(PIPE) is able to produce transition disc that for a given mass accretion rate have larger holes when compared tostandard X-ray photoevaporation. This constitutes a possible route for the formation of the observed class of accretingtransition discs with large holes, which are otherwise difficult to explain by planet formation or photoevaporation alone.Moreover, assuming that a planet is able to filter dust completely, PIPE produces a transition disc with a large holeand may provide a mechanism to quickly shut down accretion. This process appears to be too slow however to explainthe observed desert in the population of transition disc with large holes and low mass accretion rates.

Accepted by Monthly Notices of the Royal Astronomical Society


A systematic survey for eruptive young stellar objects using mid-infrared photometry

Aleks Scholz1, Dirk Froebrich2 and Kenneth Wood3

1 School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland2 Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, CT2 7NH, United Kingdom3 School of Physics and Astronomy, University of St. Andrews, The North Haugh, St. Andrews, Fife, KY16 9SS,United Kingdom

E-mail contact: aleks at cp.dias.ie

Accretion in young stellar objects (YSOs) is at least partially episodic, i.e. periods with high accretion rates (’bursts’)are interspersed by quiescent phases. These bursts manifest themselves as eruptive variability. Here we present asystematic survey for eruptive YSOs aiming to constrain the frequency of accretion bursts. We compare mid-infraredphotometry from Spitzer and WISE separated by ∼ 5 yr for two samples of YSOs, in nearby star forming regions andin the Galactic plane, each comprising about 4000 young sources. All objects for which the brightness at 3.6 and4.5µm is increased by at least 1mag between the two epochs may be eruptive variables and burst candidates. Forthese objects, we carry out follow-up observations in the near-infrared. We discover two new eruptive variables in theGalactic plane which could be FU Ori-type objects, with K-band amplitudes of more than 1.5mag. One object knownto undergo an accretion burst, V2492 Cyg, is recovered by our search as well. In addition, the young star ISO-Oph-50,previously suspected to be an eruptive object, is found to be better explained by a disk with varying circumstellarobscuration. In total, the number of burst events in a sample of 4000 YSOs is 1-4. Assuming that all YSOs undergoepisodic accretion, this constraint can be used to show that phases of strong accretion (> 10−6M⊙yr

−1) occur in

41

intervals of about 104 yr, most likely between 5000 and 50000yr. This is consistent with the dynamical timescales foroutflows, but not with the separations of emission knots in outflows, indicating that episodic accretion could eithertrigger or stop collimated large-scale outflows.

Accepted by MNRAS


How Significant is Radiation Pressure in the Dynamics of the Gas Around Young StellarClusters?

Sergiy Silich and Guillermo Tenorio-Tagle

1 Instituto Nacional de Astrofısica Optica y Electronica, AP 51, 72000 Puebla, Mexico

E-mail contact: silich at inaoep.mx

The impact of radiation pressure on the dynamics of the gas in the vicinity of young stellar clusters is thoroughlydiscussed. The radiation over the thermal/ram pressure ratio time evolution is calculated explicitely and the crucialrole of the cluster mechanical power and of the strong time evolution of the ionizing photon flux and of the bolometricluminosity of the exciting cluster is stressed. It is shown that radiation has only a narrow window of opportunity todominate the wind-driven shell dynamics. This may occur only at early stages of the bubble evolution and if the shellexpands into a dusty and/or a very dense proto-cluster medium. The impact of radiation pressure on the wind-drivenshell becomes always negligible after about 3 Myr. Finally, the wind-driven model results allow one to compare themodel predictions with the distribution of thermal pressure derived from X-ray observations. The shape of the thermalpressure profile allows then to distinguish between the energy and the momentum dominated regimes of expansionand thus conclude whether radiative losses of energy or the leakage of hot gas from the bubble interior have beensignificant during the bubble evolution.

Accepted by ApJ


A Herschel and APEX Census of the Reddest Sources in Orion: Searching for theYoungest Protostars

Amelia M. Stutz1, John J. Tobin2, Thomas Stanke3, S. Thomas Megeath4, William J. Fischer4, ThomasRobitaille1, Thomas Henning1, Babar Ali5, James di Francesco6, Elise Furlan7,5, Lee Hartmann8, MayraOsorio9, Thomas L. Wilson10, Lori Allen7, Oliver Krause1 and P. Manoj11

1 Max Planck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg, Germany2 Hubble Fellow, National Radio Astronomy Observatory, Charlottesville, VA 22903, USA3 ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Munchen, Germany4 Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606, USA5 NHSC/IPAC/Caltech, 770 S. Wilson Avenue, Pasadena, CA 91125, USA6 National Research Council of Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Rd., Victoria, BC,V9E 2E7, Canada; University of Victoria, Department of Physics and Astronomy, PO Box 3055, STN CSC, Victoria,BC, V8W 3P6, Canada7 National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ, 85719, USA8 Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109,USA9 Instituto de Astrofısica de Andalucıa, CSIC, Camino Bajo de Huetor 50, E-18008, Granada, Spain10 Naval Research Laboratory, 4555 Overlook Ave. SW, Washington, DC 20375, USA11 Department of Physics and Astronomy, 500 Wilson Blvd., University of Rochester, Rochester, NY 14627, USA

E-mail contact: stutz at mpia.de

We perform a census of the reddest, and potentially youngest, protostars in the Orion molecular clouds using dataobtained with the PACS instrument onboard the Herschel Space Observatory and the LABOCA and SABOCA instru-ments on APEX as part of the Herschel Orion Protostar Survey (HOPS). A total of 55 new protostar candidates aredetected at 70 µm and 160 µm that are either too faint (m24 > 7 mag) to be reliably classified as protostars or unde-

42

tected in the Spitzer/MIPS 24 µm band. We find that the 11 reddest protostar candidates with log λFλ70/λFλ24 > 1.65are free of contamination and can thus be reliably explained as protostars. The remaining 44 sources have less ex-treme 70/24 colors, fainter 70 µm fluxes, and higher levels of contamination. Taking the previously known sample ofSpitzer protostars and the new sample together, we find 18 sources that have log λFλ70/λFλ24 > 1.65; we name thesesources ”PACS Bright Red sources”, or PBRs. Our analysis reveals that the PBRs sample is composed of Class 0 likesources characterized by very red SEDs (Tbol < 45 K) and large values of sub–millimeter fluxes (Lsmm/Lbol > 0.6%).Modified black–body fits to the SEDs provide lower limits to the envelope masses of 0.2 M⊙ to 2 M⊙ and luminositiesof 0.7 L⊙ to 10 L⊙. Based on these properties, and a comparison of the SEDs with radiative transfer models ofprotostars, we conclude that the PBRs are most likely extreme Class 0 objects distinguished by higher than typicalenvelope densities and hence, high mass infall rates.

Accepted by ApJ


High-pressure, low-abundance water in bipolar outflows. Results from a Herschel-WISHsurvey

M. Tafalla1, R. Liseau2, B. Nisini3, R. Bachiller1, J. Santiago-Garcıa4, E. F. van Dishoeck5,6, L. E.Kristensen5, G. J. Herczeg6,7, and U. A. Yıldız5

1Observatorio Astronomico Nacional (IGN), Alfonso XII 3, E-28014 Madrid, Spain2Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92Onsala, Sweden3INAF - Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy4Instituto de Radioastronomıa Milimetrica (IRAM), Avenida Divina Pastora 7, Nucleo Central, 18012 Granada, Spain5Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands6Max-Planck Institut fur Extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748 Garching, Germany7Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian Qu, 100871 Beijing,P.R. China

E-mail contact: m.tafalla at oan.es

Context. Water is a potential tracer of outflow activity because it is heavily depleted in cold ambient gas and iscopiously produced in shocks.Aims. We present a survey of the water emission in a sample of more than 20 outflows from low-mass young stellarobjects with the goal of characterizing the physical and chemical conditions of the emitting gas.Methods. We used the HIFI and PACS instruments on board the Herschel Space Observatory to observe the twofundamental lines of ortho-water at 557 and 1670 GHz. These observations were part of the “Water In Star-formingregions with Herschel” (WISH) key program, and have been complemented with CO and H2 data.Results. The emission of water has a different spatial and velocity distribution from that of the J=1-0 and 2-1transitions of CO. On the other hand, it has a similar spatial distribution to H2, and its intensity follows the H2

intensity derived from IRAC images. This suggests that water traces the outflow gas at hundreds of kelvins that isresponsible for the H2 emission, and not the component at tens of kelvins typical of low-J CO emission. A warm originof the water emission is confirmed by a remarkable correlation between the intensities of the 557 and 1670 GHz lines,which also indicates that the emitting gas has a narrow range of excitations. A radiative transfer analysis shows thatwhile there is some ambiguity in the exact combination of density and temperature values, the gas thermal pressurenT is constrained within less than a factor of 2. The typical nT over the sample is 4×109 cm−3K, which represents anincrease of 104 with respect to the ambient value. The data also constrain the water column density within a factor of2 and indicate values in the sample between 2× 1012 and 1014 cm−2. When these values are combined with estimatesof the H2 column density, the typical water abundance is only 3× 10−7, with an uncertainty of a factor of 3.Conclusions. Our data challenge current C-shock models of water production through the combination of wing-lineprofiles, high gas compressions, and low abundances.

Accepted by Astronomy and Astrophysics


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Imaging Discovery of the Debris Disk Around HIP 79977

C. Thalmann1, M. Janson2, E. Buenzli3, T. D. Brandt2, J. P. Wisniewski4, C. Dominik1, J. Carson5,M. W. McElwain6, T. Currie7, G. R. Knapp2, A. Moro-Martın8, T. Usuda9, L. Abe10, W. Brandner11,S. Egner9, M. Feldt11, T. Golota9, M. Goto12, O. Guyon9, J. Hashimoto13, Y. Hayano9, M. Hayashi9, S.Hayashi9, T. Henning11, K. W. Hodapp14, M. Ishii9, M. Iye13, R. Kandori13, T. Kudo13, N. Kusakabe13,M. Kuzuhara13,15, J. Kwon16,13, T. Matsuo13, S. Mayama16, S. Miyama13, J.-I. Morino13, T. Nishimura9,T.-S. Pyo9, E. Serabyn17, H. Suto13, R. Suzuki13, M. Takami18, N. Takato9, H. Terada9, D. Tomono9,E. L. Turner2,19, M. Watanabe20, T. Yamada21, H. Takami9, M. Tamura13

1 Astronomical Institute ”Anton Pannekoek”, University of Amsterdam, Amsterdam, The Netherlands2 Department of Astrophysical Sciences, Princeton University, USA3 Department of Astronomy and Steward Observatory, University of Arizona, Tucson AZ, USA4 H.L. Dodge Dept. of Physics & Astronomy, Univ. of Oklahoma, USA5 College of Charleston, Charleston, South Carolina, USA6 NASA Goddard Space Flight Center, Greenbelt MD, USA7 University of Toronto, Toronto, Canada8 Department of Astrophysics, CAB-CSIC/INTA, Madrid, Spain9 Subaru Telescope, Hilo, Hawaii, USA10 Laboratoire Hippolyte Fizeau, Nice, France11 Max Planck Institute for Astronomy, Heidelberg, Germany12 Ludwig-Maximilians-Universitat, Munich, Germany13 National Astronomical Observatory of Japan, Tokyo, Japan 14 Institute for Astronomy, University of Hawaii, Hilo,Hawaii, USA15 University of Tokyo, Tokyo, Japan16 Graduate Univ. for Adv. Studies (Sokendai), Shonan Village, Japan17 NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena CA, USA18 Inst. of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan19 Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo, Japan20 Department of Cosmosciences, Hokkaido University, Sapporo, Japan21 Astronomical Institute, Tohoku University, Sendai, Japan

E-mail contact: thalmann at uva.nl

We present Subaru/HiCIAO H-band high-contrast images of the debris disk around HIP 79977, whose presence wasrecently inferred from an infrared excess. Our images resolve the disk for the first time, allowing characterizationof its shape, size, and dust grain properties. We use angular differential imaging (ADI) to reveal the disk geometryin unpolarized light out to a radius of ∼2′′, as well as polarized differential imaging (PDI) to measure the degree ofscattering polarization out to ∼1.5′′. In order to strike a favorable balance between suppression of the stellar halo andconservation of disk flux, we explore the application of principal component analysis (PCA) to both ADI and referencestar subtraction. This allows accurate forward modeling of the effects of data reduction on simulated disk images,and thus direct comparison with the imaged disk. The resulting best-fit values and well-fitting intervals for the modelparameters are a surface brightness power-law slope of Sout = −3.2 [−3.6,−2.9], an inclination of i = 84◦ [81◦, 86◦],a high Henyey-Greenstein forward-scattering parameter of g = 0.45 [0.35, 0.60], and a non-significant disk-star offsetof u = 3.0 [−1.5, 7.5] AU = 24 [−13, 61] mas along the line of nodes. Furthermore, the tangential linear polarizationalong the disk rises from ∼10% at 0.5′′ to ∼45% at 1.5′′. These measurements paint a consistent picture of a disk ofdust grains produced by collisional cascades and blown out to larger radii by stellar radiation pressure.

Accepted by ApJL


Resolved Depletion Zones and Spatial Differentiation of N2H+ and N2D+

John Tobin1,2, Edwin A. Bergin2, Lee Hartmann2, Jeong-Eun Lee3, Sebastien Maret4, Phillip C. Myers5,Leslie W. Looney6, Hsin-Fang Chiang6,7 and Rachel Friesen1

1 NRAO Charlottesville, USA2 University of Michigan, USA

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3 Kyung Hee University, Korea4 IPAG, France5 Harvard-Smithsonian Center for Astrophysics, USA6 University of Illinois, USA7 University of Hawaii at Manoa, USA

E-mail contact: jtobin at nrao.edu

We present a study on the spatial distribution of N2D+ and N2H+ in thirteen protostellar systems. Eight of thirteenobjects observed with the IRAM 30m telescope show relative offsets between the peak N2D+ (J=2-1) and N2H+(J=1-0) emission. We highlight the case of L1157 using interferometric observations from the Submillimeter Arrayand Plateau de Bure Interferometer of the N2D+ (J=3-2) and N2H+ (J=1-0) transitions respectively. Depletion ofN2D+ in L1157 is clearly observed inside a radius of 2000 AU (7”) and the N2H+ emission is resolved into twopeaks at radii of 1000 AU (3.5”), inside the depletion region of N2D+. Chemical models predict a depletion zone inN2H+ and N2D+ due to destruction of H2D+ at T 20 K and the evaporation of CO off dust grains at the sametemperature. However, the abundance offsets of 1000 AU between the two species are not reproduced by chemicalmodels, including a model that follows the infall of the protostellar envelope. The average abundance ratios of N2D+to N2H+ have been shown to decrease as protostars evolve by Emprechtinger et al., but this is the first time depletionzones of N2D+ have been spatially resolved. We suggest that the difference in depletion zone radii for N2H+ andN2D+ is caused by either the CO evaporation temperature being above 20 K or an H2 ortho-to-para ratio gradientin the inner envelope.

Accepted by ApJ


Chemical abundances in Orion protoplanetary discs: integral field spectroscopy andphotoevaporation models of HST 10

Y. G. Tsamis1, N. Flores-Fajardo2, W. J. Henney2, J. R. Walsh1 and A. Mesa-Delgado3

1 ESO Garching, Germany2 Centro de Radioastronomıa y Astrofısica, UNAM-Morelia, Mexico3 Departamento de Astronomıa y Astrofısica, Facultad de Fısica, Pontificia Universidad Catolica de Chile

E-mail contact: ygtsamis at gmail.com

Photoevaporating protoplanetary discs (proplyds) in the vicinity of hot massive stars, such as those found in Orion, areimportant objects of study for the fields of star formation, early disc evolution, planetary formation, and H II regionastrophysics. Their element abundances are largely unknown, unlike those of the main-sequence stars or the hostOrion nebula. We present a spectroscopic analysis of the Orion proplyd HST 10, based on integral field observationswith the Very Large Telescope/FLAMES fibre array with 0.31′′ × 0.31′′ spatial pixels. The proplyd and its vicinity areimaged in a variety of emission lines across a 6.8′′ × 4.3′′ area. The reddening, electron density and temperature aremapped out from various line diagnostics. The abundances of helium, and eight heavy elements are measured relativeto hydrogen using the direct method based on the [O iii] electron temperature. The abundance ratios of O/H and S/Hare derived without resort to ionization correction factors. We construct dynamic photoevaporation models of HST10 with the Cloudy microphysics code that validate the oxygen and sulfur abundances. With the exception of [O i]6300 A and [S ii] 4069 A, the model fit is satisfactory for all spectral lines arising from the proplyd. The models showthat the classic ionization correction factor for neon significantly underestimates (0.4 dex) this element’s abundancein the low ionization conditions of HST 10. Apart from iron, whose gas-phase abundance is ∼0.3 dex lower than inthe local Orion nebula, most other elements in the proplyd do not show substantially different gas-phase abundancesfrom the nebula. The abundances of carbon, oxygen and neon in HST 10 are practically the same as those in B-typestars in Orion.

Accepted by Monthly Notices of the Royal Astronomical Society


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PAH Emission in the Proplyd HST10: What is the Mechanism behind Photoevapora-tion?

Sılvia Vicente1, Olivier Berne2,3, Alexander G. G. M. Tielens4, Nuria Huelamo5, Eric Pantin6, IngaKamp1 and Andres Carmona7

1 Kapteyn Astronomical Institute, Postbus 800, 9700 AV, Groningen, The Netherlands2 Universite de Toulouse; UPS-OMP; IRAP; Toulouse, France3 CNRS; IRAP; 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4, France4 Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333 CA Leiden, The Netherlands5 CAB (INTA-CSIC), LAEFF, P.O. Box 78, 28691 Villanueva de la Canada, Madrid, Spain6 Laboratoire AIM, CEA/DSM - CNRS - Universite Paris Diderot, IRFU/SAP, 91191 sur Yvette, France7 UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et et d’Astrophysique de Grenoble (IPAG) UMR 5274,Grenoble, F-38041, France

E-mail contact: vicente at astro.rug.nl

Proplyds are photodissociation region (PDR)-like cometary cocoons around young stars which are thought to originatethrough photo-evaporation of the central protoplanetary disk by external UV radiation from the nearby OB stars.This letter presents spatially resolved mid-infrared imaging and spectroscopy of the proplyd HST10 obtained with theVLT/VISIR instrument. These observations allow us to detect Polycyclic Aromatic Hydrocarbons (PAH) emission inthe proplyd photodissociation region and to study the general properties of PAHs in proplyds for the first time. Wefind that PAHs in HST10 are mostly neutral and at least 50 times less abundant than typical values found for thediffuse ISM or the nearby Orion Bar. With such a low PAH abundance, photoelectric heating is significantly reduced.If this low abundance pertains also to the original disk material, gas heating rates could be too low to efficiently drivephotoevaporation unless other processes can be identified. Alternatively, the model behind the formation of proplydsas evaporating disks may have to be revised.

Accepted by Astrophysical Journal Letters


Comparing the Ancient Star Formation Histories of the Magellanic Clouds

Daniel R. Weisz1, Andrew E. Dolphin2, Evan D. Skillman3, Jon Holtzman4, Julianne J. Dalcanton1,Andrew A. Cole5, and Kyle Neary3

1 1epartment of Astronomy, Box 351580, University of Washington, Seattle, WA 981952 Raytheon, 1151 E. Hermans Road, Tucson, AZ 857563 Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA4 Department of Astronomy, New Mexico State University, Box 30001, 1320 Frenger St., Las Cruces, NM 880035 School of Mathematics and Physics, University of Tasmania, Hobart, Tasmania, Australia

E-mail contact: dweisz at astro.washington.edu

We present preliminary results from a new HST archival program aimed at tightly constraining the ancient (>4 Gyrago) star formation histories (SFHs) of the field populations of the SMC and LMC. We demonstrate the qualityof the archival data by constructing HST/WFPC2-based color-magnitude diagrams (CMDs; MF555W ∼ +8) for 7spatially diverse fields in the SMC and 8 fields in the LMC. The HST-based CMDs are >2 magnitudes deeper thanany from ground based observations, and are particularly superior in high surface brightness regions, e.g., the LMCbar, which contain a significant fraction of star formation and are crowding limited from ground based observations.To minimize systematic uncertainties, we derive the SFH of each field using an identical maximum likelihood CMDfitting technique. We then compute an approximate mass weighted average SFH for each galaxy. We find that bothgalaxies lack a dominant burst of early star formation, which suggests either a suppression or an under-fueling of earlystar formation. From 10-12 Gyr ago, the LMC experienced a period of enhanced stellar mass growth relative to theSMC. Similar to some previous studies, we find two notable peaks in the SFH of the SMC at ∼4.5 and 9 Gyr ago,which could be due to repeated close passages with the LMC, implying an interaction history that has persisted forat least 9 Gyr. We find little evidence for strong periodic behavior in the lifetime SFHs of both MCs, suggesting thatrepeated encounters with the Milky Way are unlikely. Beginning ∼3.5 Gyr ago, both galaxies show increases in theirSFHs, in agreement with previous studies, and thereafter, track each other remarkably well. (abridged)

46

Accepted by MNRAS


Widespread Methanol Emission from the Galactic Center

F. Yusef-Zadeh1, W. Cotton2, S. Viti3, M. Wardle4, and M. Royster1

1: Department of Physics and Astronomy, Northwestern University, Evanston, Il. 60208, USA2 National Radio Astronomy Observatory, Charlottesville, VA 22903, USA3 Department of Physics and Astronomy, University College London, Gower St. London, WCIE 6BT, UK4 Department of Physics & Astronomy, Macquarie University, Sydney NSW 2109, Australia

E-mail contact: [email protected]

We report the discovery of a widespread population of collisionally excited methanol J = 4−1 to 30 E sources at 36.2GHz from the inner 66′ × 18′ (160×43 pc) of the Galactic center. This spectral feature was imaged with a spectralresolution of 16.6 km s−1 taken from 41 channels of a VLA continuum survey of the Galactic center region. Therevelation of 356 methanol sources, most of which are maser candidates, suggests a large abundance of methanol in thegas phase in the Galactic center region. There is also spatial and kinematic correlation between SiO (2–1) and CH3OHemission from four Galactic center clouds: the +50 and +20 km s−1 clouds and G0.13-0.13 and G0.25+0.01. Theenhanced abundance of methanol is accounted for in terms of induced photodesorption by cosmic rays as they travelthrough a molecular core, collide, dissociate, ionize, and excite Lyman Werner transitions of H2. A time-dependentchemical model in which cosmic rays drive the chemistry of the gas predicts CH3OH abundance of 10−8 to 10−7 on achemical time scale of 5× 104 to 5× 105 years. The average methanol abundance produced by the release of methanolfrom grain surfaces is consistent with the available data.

Accepted by ApJL (764:L19)


ALMA 690 GHz observations of IRAS 16293-2422B: Infall in a highly optically-thickdisk

Luis A. Zapata1, Laurent Loinard1,2, Luis F. Rodrıguez1,3, Vicente Hernandez1, Satoko Takahashi4,Alfonso Trejo4 , and Berengere Parise2

1 Centro de Radioastronomıa y Astrofısica, UNAM, Apdo. Postal 3-72 (Xangari), 58089 Morelia, Michoacan, Mexico2 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121,Bonn, Germany3 Astronomy Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia4 Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan

E-mail contact: lzapata at crya.unam.mx

We present sensitive, high angular resolution (∼ 0.2′′) submillimeter continuum and line observations of IRAS 16293-2422B made with the Atacama Large Millimeter/Submillimeter Array (ALMA). The 0.45 mm continuum observationsreveal a single and very compact source associated with IRAS 16293-2422B. This submillimeter source has a decon-volved angular size of about 400 milli-arcseconds (50 AU), and does not show any inner structure inside of thisdiameter. The H13CN, HC15N, and CH3OH line emission regions are about twice as large as the continuum emissionand reveal a pronounced inner depression or ”hole” with a size comparable to that estimated for the submillimetercontinuum. We suggest that the presence of this inner depression and the fact that we do not see inner structure (ora flat structure) in the continuum is produced by very optically thick dust located in the innermost parts of IRAS16293-2422B. All three lines also show pronounced inverse P-Cygni profiles with infall and dispersion velocities largerthan those recently reported from observations at lower frequencies, suggesting that we are detecting faster, and moreturbulent gas located closer to the central object. Finally, we report a small east-west velocity gradient in IRAS16293-2422B that suggests that its disk plane is likely located very close to the plane of the sky.

Accepted by ApJL


47

γ Doradus pulsation in two pre-main sequence stars discovered by CoRoT

K. Zwintz1,2, L. Fossati3, T. Ryabchikova4, A. Kaiser1, M. Gruberbauer5, T. G. Barnes6, A. Baglin7,and S. Chaintreuil7

1 University of Vienna, Institute of Astronomy, Turkenschanzstrasse 17, A-1180 Vienna, Austria2 Instituut voor Sterrenkunde, K. U. Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium3 Argelander-Institut fur Astronomie der Universitat Bonn, Auf dem Hugel 71, 53121 Bonn, Germany4 Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 119017 Moscow, Russia5 Department of Astronomy and Physics, St. Marys University, Halifax, NS B3H 3C3, Canada6 The University of Texas at Austin, McDonald Observatory, 82 Mt. Locke Rd., McDonald Observatory, Texas 79734,USA7 LESIA, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon, France

E-mail contact: konstanze.zwintz at univie.ac.at

Context. Pulsations in pre-main sequence stars have been discovered several times within the last years. But nearlyall of these pulsators are of δ Scuti-type. γ Doradus-type pulsation in young stars has been predicted by theory, butlack observational evidence.Aims. We present the investigation of variability caused by rotation and (γ Doradus-type) pulsation in two pre-mainsequence members of the young open cluster NGC 2264 using high-precision time series photometry from the CoRoTsatellite and dedicated high-resolution spectroscopy.Methods. The variability found using the CoRoT data was combined with the fundamental parameters and chemicalabundances derived from high-resolution spectroscopy, obtained at the Mc Donald Observatory, to discuss the presenceof pulsation and rotation in the two NGC 2264 cluster members. Time series photometry of NGC 2264 VAS 20 andNGC 2264 VAS 87 was obtained by the CoRoT satellite during the dedicated short run SRa01 in March 2008. NGC2264 VAS 87 was re-observed by CoRoT during the short run SRa05 in December 2011 and January 2012. Frequencyanalysis was conducted using Period04 and SigSpec. The spectral analysis was performed using equivalent widths andspectral synthesis.Results. The frequency analysis yielded ten and fourteen intrinsic frequencies for NGC 2264 VAS 20 and NGC 2264VAS 87, respectively, in the range from 0 to 1.5d−1 which are attributed to be caused by a combination of rotationand pulsation. The effective temperatures were derived to be 6380±150 K for NGC 2264 VAS 20 and 6220±150 Kfor NGC 2264 VAS 87. Membership of the two stars to the cluster is confirmed independently using X-ray fluxes,radial velocity measurements and proper motions available in the literature. The derived Lithium abundances of logn(Li) = 3.34 and 3.54 for NGC 2264 VAS 20 and NGC 2264 VAS 87, respectively, are in agreement with the Lithiumabundance for other stars in NGC 2264 of similar Teff reported in the literature.Conclusions. We conclude that the two objects are members of NGC 2264 and therefore are in their pre-main sequenceevolutionary stage. Their variability is attributed to be caused by rotation and g-mode pulsation rather than rotationonly. Assuming that part of their variability is caused by pulsation, these two stars might be the first pre-mainsequence γ Doradus candidates.

Accepted by A&A


48

Abstracts of recently accepted major reviews

Essential Magnetohydrodynamics for Astrophysics

H.C. Spruit

1 Max Planck Institute for Astrophysics

E-mail contact: henk at mpa-garching.mpg.de

This text is intended as an introduction to magnetohydrodynamics in astrophysics, emphasizing a fast path to theelements essential for physical understanding. It assumes experience with concepts from fluid mechanics: the fluidequation of motion and the Lagrangian and Eulerian descriptions of fluid flow. In addition, the basics of vector calculusand elementary special relativity are needed. Not much knowledge of electromagnetic theory is required. In fact, sinceMHD is much closer in spirit to fluid mechanics than to electromagnetism, an important part of the learning curveis to overcome intuitions based on the vacuum electrodynamics of one’s high school days. The first chapter (only 36pp) is meant as a practical introduction including exercises. This is the ’essential’ part. The exercises are importantas illustrations of the points made in the text (especially the less intuitive ones). Almost all are mathematicallyunchallenging. The supplement in chapter 2 contains further explanations, more specialized topics and connections tothe occasional topic somewhat outside MHD. The emphasis is on physical understanding by the visualization of MHDprocesses, as opposed to more formal approaches.

Available at http://arxiv.org/pdf/1301.5572

Moving ... ??

If you move or your e-mail address changes, pleasesend the editor your new address. If the Newsletterbounces back from an address for three consecutivemonths, the address is deleted from the mailing list.

49

Dissertation Abstracts

Water in molecular outflows and shocks:Studies with Odin and Herschel

Per Bjerkeli

Thesis work conducted at: Chalmers University of Technology

Current address: Dept. of Earth & Space Sciences, Chalmers University of Technology, SE-439 92 Onsala, Sweden

Electronic mail: [email protected]

Ph.D dissertation directed by: Prof. Malcolm Walmsley

Ph.D. degree awarded: November 2012

This thesis describes observations and analyses of water in molecular outflows from young stellar objects. The abun-dance of this molecule (with respect to molecular hydrogen) is deduced from observations carried out primarily withthe Odin and Herschel telescopes. The large spatial extents of molecular outflows allow for mapping observationsto be done, but in addition to this, spectroscopy allows for the investigation of the kinematics. The observationsdiscussed in this thesis were acquired over the years 2002 to 2011.

In the first appended research paper, observations of 15 different shocked regions are reported. The targets wereprimarily molecular outflows, but two supernova remnants were also observed. This study shows that the waterabundance in the gas is elevated in the presence of shock waves. Furthermore, the water abundance seems to correlatewith the maximum velocity of the shocked gas.

In the second paper, previously published observations of the Herbig-Haro object HH 54 are followed up, using APEX,Odin and Herschel. In this work we investigate the relative cooling contribution from CO and H2O and we comparethe results with most recent shock models. CO dominates the cooling and we conclude that planar shock modelsdo not explain the observations satisfactorily. Instead we find that a curved geometry can completely account forthe observed line profile shapes in the two species. The inferred water abundance is lower than what was previouslyexpected.

In the third paper, Herschel mapping observations of VLA 1623 are presented. The ground-state transitions of o-H2Owere mapped using the HIFI and PACS instruments but also higher energy transitions were observed towards selectedpositions in the outflow lobes. The observed H2O(110 − 101) line profiles show a variety of shapes over the observedregion and also from this work, we conclude that the water abundance is lower than expected. In addition to this,it is now clear that the regions responsible for the emission in water are warmer than the regions traced by CO. Acomparison with H2 data obtained with Spitzer allows us to estimate the physical parameters of the flow. This leadsus to conclude, that it does not matter which molecular tracer we use when we infer the force and the power of theVLA1623 outflow. The analysis is followed up in a letter where we include also the L 1448 and L 1157 outflows.

http://publications.lib.chalmers.se/publication/165339-water-in-molecular-outflows-and-shocks-studies-with

50

A Critical Assessment of Ages Derived Using Pre-Main-SequenceIsochrones in Colour-Magnitude Diagrams

Cameron P. M. Bell

University of Exeter, UK

Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK

Electronic mail: bell at astro.ex.ac.uk

Ph.D dissertation directed by: Prof. Tim Naylor

Ph.D degree awarded: November 2012

In this thesis a critical assessment of the ages derived using theoretical pre-main-sequence (pre-MS) stellar evolutionarymodels is presented by comparing the predictions to the low-mass pre-MS population of 14 young star-forming regions(SFRs) in colour-magnitude diagrams (CMDs).

Deriving pre-MS ages requires precise distances and estimates of the reddening. Therefore, the main-sequence (MS)members of the SFRs have been used to derive a self-consistent set of statistically robust ages, distances and reddeningswith associated uncertainties using a maximum-likelihood fitting statistic and MS evolutionary models. A photometricmethod (known as the Q-method) for de-reddening individual stars in regions where the extinction is spatially variablehas been updated and is presented. The effects of both the model dependency and the SFR composition on thesederived parameters are also discussed.

The problem of calibrating photometric observations of red pre-MS stars is examined and it is shown that usingobservations of MS stars to transform the data into a standard photometric system can introduce significant errorsin the position of the pre-MS locus in CMD space. Hence, it is crucial that precise photometric studies (especiallyof pre-MS objects) be carried out in the natural photometric system of the observations. This therefore requires arobust model of the system responses for the instrument used, and thus the calculated responses for the Wide-FieldCamera on the Isaac Newton Telescope are presented. These system responses have been tested using standard starobservations and have been shown to be a good representation of the photometric system.

A benchmark test for the pre-MS evolutionary models is performed by comparing them to a set of well-calibratedCMDs of the Pleiades in the wavelength regime 0.4 − 2.5µm. The masses predicted by these models are also testedagainst dynamical masses using a sample of MS binaries by calculating the system magnitude in a given photometricbandpass. This analysis shows that for Teff ≤ 4000K the models systematically overestimate the flux by a factor of2 at 0.5µm, though this decreases with wavelength, becoming negligible at 2.2µm. Thus before the pre-MS modelsare used to derive ages, a recalibration of the models is performed by incorporating an empirical colour-Teff relationand bolometric corrections based on the Ks-band luminosity of Pleiades members, with theoretical corrections for thedependence on the surface gravity (log g).

The recalibrated pre-MS model isochrones are used to derive ages from the pre-MS populations of the SFRs. Theseages are then compared with the MS derivations, thus providing a powerful diagnostic tool with which to discriminatebetween the different pre-MS age scales that arise from a much stronger model dependency in the pre-MS regime.The revised ages assigned to each of the 14 SFRs are up to a factor two older than previous derivations, a result withwide-ranging implications, including that circumstellar discs survive longer and that the average Class II lifetime isgreater than currently believed.

http://www.astro.ex.ac.uk/people/bell/thesis.pdf

51

The evolution of protoplanetary disks in T Tauri binary systems

Sebastian Daemgen

European Southern Observatory, Garching / LMU

Dept. of Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, Canada M5S 3H4

Electronic mail: daemgen at astro.utoronto.ca

Ph.D dissertation directed by: Monika Petr-Gotzens & Thomas Preibisch

Ph.D degree awarded: Oct 2012

Binary stars are among the most common outcome of star formation. However, many details remain to be explored ofhow binarity influences the evolution of primordial circumstellar disks, the birthplaces of planets. Tidal interactionsand irradiation can change disk geometries and lifetimes, dust properties, and thus the conditions for planet formation.

This thesis presents high-spatial resolution near-infrared photometric and spectroscopic observations of 52 visualmultiple stars with projected separations of 25–1000AU in the Orion Nebula Cluster and Chamaeleon I star-formingregions. It represents the largest coherent study of protoplanetary disks around the individual components of TTauribinary stars in the two regions, and is among the largest of its kind in nearby star-forming regions to date. The data areused to infer individual stellar (e.g. effective temperature, luminosity, age, mass) and binary parameters (separation,component mass ratio). These are brought into context with disk parameters of each component: ongoing accretionis inferred from the strength of Brackett-γ emission and the existence of hot dust at the inner rim of the circumstellardisk is measured from near-IR excess emission.

The new results show a significant reduction of the frequency of accretion disks around binary components comparedto single stars in the same regions. The effect is strongest in close binaries with <100AU projected separation wherethe frequency of accretors among the binary components is less than 1/2 of the single star accretor fraction. Whilethese close systems also show a mild reduction of targets with hot circumstellar dust, wider binaries have a dust diskfraction comparable to single stars. The derived mass accretion rates were measured to not depend on the fact thatstars are accompanied by binary companions at separations of ∼100–1000AU.

The new results are put into context with findings from the fields of star formation, disk evolution, and planet formationto derive the following conclusions: (a) Binary components form simultaneously. Capture is not the major binaryformation process. (b) Disk evolution is accelerated in binary stars of separations <100AU compared to single stars ofthe same mass. (c) Opposite to single star disk evolution, the disk around the less massive component has on averagea shorter lifetime than the more massive component’s disk. (d) While the lifetime of a disk depends on the diameterof a disk, mass accretion rates are independent of a disk’s size and lifetime. A possible reason is a decoupling of innerand outer disk properties. (e) The correlation of disk and planet statistics around binary components supports arapid formation of gas planets with masses ≥1MJup (through e.g. disk fragmentation) and a slower process (e.g. coreaccretion) for lower-mass planets.

http://lepus.astro.utoronto.ca/~daemgen/Daemgen_PhDT.pdf

52

Meeting Announcements

VLTI school 2013 - High angular resolution for stellar astrophysicsStellar activity, surface dynamics, fundamental parameters,

exoplanetary systems, pulsations

With the advent of large and multi-telescope arrays in the recent years, interferometry has reached a new area.Interferometric facilities are becoming more and more open to non-specialist astronomers, and the Very Large TelescopeInterferometer (VLTI) is a good example of a interferometric fully open facility. We organize a summer school to trainastrophysicists to the use of the VTLI and also other facilities with the current generations of instruments. The aimof the school is to offer to Ph.D. students, post-doctoral and permanent researchers and introduction to the techniqueof long-baseline optical/infrared stellar interferometry, data reduction, astrophysics, namely: stellar physics includingthe hot topics of stellar activity, evolution, hydrodynamics, star hosting planets, the determination of the fundamentalparameters, circumstellar envelopes, young stellar objects, as well as the role of binaries. The school will be held inthe heart of Alpine mountains in Barcelonnette, Cte d’Azur, France from 9th-21st September 2013. Barcelonnetteis a typical alpine town, located in the heart of the Mercantour French National Park, with many possibilities ofsportive and non-sportive activities like hiking, or wildlife discovery. The school will also be located at one throw ofthe Hypertelescope prototype under construction, which is a novel type of stellar interferometer (a visit is foreseenduring the school).

IMPORTANT DATES

February 1st, 2013 : First announcement and web site

February 15th, 2013 : Early registration opened

May 31st, 2013 : Deadline for financial support

June 30th, 2013 : Deadline for early registration and payment (100 euro)

July 31th, 2013 : Deadline for late registration and payment (150 euro)

September 9th, 2013 : The VLTI-school starts

Please visit http://vltischool.sciencesconf.org

On behalf of the Scientific Organizing Committee,

Andrea Chiavassa

53

The Universe Explored by Herschel

15-18 October 2013

ESTEC, Noordwijk, The Netherlands

The Herschel ‘First Results Symposium’ was held in May 2010 in the ESTEC Conference Centre. More than 400astronomers shared in the excitement during the four memorable days of the first major scientific symposium featuringHerschel results. There have been numerous expressions of interest regarding future meetings. The organisers are nowpleased to be in a position to extend an invitation to the community for a follow-up meeting.

The overall objective of ‘The Universe Explored by Herschel’ meeting will be to present, discuss, and take stock ofthe scientific breakthroughs to date based on Herschel observations, and their impact. The symposium will featureinvited and contributed talks, and posters, in five sessions:

• Galaxy formation & evolution

• Large scale galactic structure & nearby galaxies

• Water, astrochemistry & ISM physics

• Star & planetary system formation & evolution

• The Solar System & its evolution

The Second Announcement and Call for Papers was issued on 25 January 2013, the deadline for abstract submissionis 31 May 2013. All information about the meeting is available on the conference website below.

Website: http://congrexprojects.com/13a12/

Contact: [email protected]

54

Physics at the Magnetospheric Boundary

(Neutron Stars, White Dwarfs and Young Stellar Objects)

University of Geneva, Switzerland (25-28 June 2013)

Registration and Grant applications openEarly registration deadline: 8 AprilLate registration deadline: 27 May

Grant application deadline: 15 March

The ”Physics at the Magnetospheric Boundary” conference is aimed at bringing together specialists working theoreti-cally, numerically and observationally on processes occurring at the limit of the magnetically dominated region aroundaccreting objects such as: Neutron Stars, White Dwarfs, and Young Stellar Objects.

The conference represents a precious opportunity of exchange between research groups working on the topic of accre-tion, across different wavelengths and source types. It poses the basis for the next steps forward in our understandingof the physics at the magnetospheric boundary.

Planned sessions for the conference include:

• Theory of accretion onto magnetized stars

• Numerical modelling of plasma-field interaction: accretion and jets production

• Observational clues to the physics at the magnetosphere

• Future perspectives in theory and observations

Registration and grant applications for students:http://www.isdc.unige.ch/magbound/index.php/registration

Invited Speakers, Program and other details are available on the conference website:http://www.isdc.unige.ch/magbound/

For any information, please contact: [email protected]

55

Other Meetings of Possible Interest

Characterising Exoplanets: Detection, Formation, Interiors, Atmospheres and Habitability11 - 12 March 2013 The Royal Society, London, UKhttp://royalsociety.org/events/2013/exoplanets/

43nd Saas-Fee Course: Star Formation in Galaxy Evolution: Connecting Numerical Models to Reality11 - 16 March 2013 Villars-sur-Ollon, Switzerlandhttp://lastro.epfl.ch/conferences/sf2013

Infrared and Submillimeter Probes of Gas in Galaxies: From the Milky Way to the Distant Universe17 - 20 March 2013 Pasadena, CA USAhttp://conference.ipac.caltech.edu/gasconf/

From Stars to Life - Connecting our Understanding of Star Formation, Planet Formation, Astrochem-istry and Astrobiology3 - 6 April 2013 Gainesville, Florida, USAhttp://conference.astro.ufl.edu/STARSTOLIFE/

StarBench: A Workshop for the Benchmarking of Star Formation Codes8 - 11 April 2013 University of Exeter, UKhttp://www.astro.ex.ac.uk/people/haworth/workshop_bench/index.html

Transformational Science with ALMA: From Dust to Rocks to Planets - Formation and Evolution ofPlanetary Systems8 - 12 April 2013 Hilton Waikoloa Village, The Big Island of Hawaii, USAhttp://www.cv.nrao.edu/rocks/index.html

International Young Astronomer School on Exploiting the Herschel and Planck data15 - 19 April 2013 Meudon, Francehttp://ufe.obspm.fr/rubrique344.html

Habitable Worlds Across Time and Space29 April - 2 May 2013 Space Telescope Science Institute, Baltimore, USAhttp://www.stsci.edu/institute/conference/habitable-worlds

Ice and Planet Formation15 - 17 May 2013 Lund Observatory, Swedenhttp://www.astro.lu.se/~anders/IPF2013/

IAU Symposium 297: The Diffuse Interstellar Bands20 - 24 May 2013 Noordwijkerhout, The Netherlandshttp://iau297.nl/

Brown Dwarfs come of Age20 - 24 May 2013 Fuerteventura, Canary Islands, Spainno web site yet

The Origins of Stellar Clustering - from Fragmenting Clouds to the Build-up of Galaxies26 May 2013 - 16 June 2013 Aspen, Colorado, USAhttp://www.mpa-garching.mpg.de/~diederik/aspen2013

56

IAU Symposium 299: Exploring the Formation and Evolution of Planetary Systems2 - 7 June 2013 Victoria, BC, Canadahttp://www.iaus299.org

Massive Stars: From alpha to Omega10 - 14 June 2013 Rhodes, Greecehttp://a2omega.astro.noa.gr

Lin-Shu Symposium: Celebrating the 50th Anniversary of the Density-Wave Theory24 - 28 June 2013 Beijing, Chinano web site yet

Protostars and Planets VI15 - 20 July 2013 Heidelberg, Germanyhttp://www.ppvi.org

Dust Growth in Star & Planet Formation 201322 - 25 July 2013 MPIA, Heidelberg, Germanyno web site yet

2013 Sagan Summer Workshop: Imaging Planets and Disks29 July - 2 August 2013 Pasadena, CA, USAhttp://nexsci.caltech.edu/workshop/2013/

IAUS 302 - Magnetic Fields Throughout Stellar Evolution26 - 30 August 2013 Biarritz, Francehttp://iaus302.sciencesconf.org

Meteoroids 2013. An International Conference on Minor Bodies in the Solar System26 - 30 August 2013 Dep. of Physics, A.M. University, Poznan, Polandhttp://www.astro.amu.edu.pl/Meteoroids2013/index.php

Exoplanets and Brown Dwarfs2 - 5 September 2013 de Havilland, University of Hertfordshire, Hatfield, Nr. London, UKno web site yet

The Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments18 - 22 November 2013 Taipei, Taiwanhttp://events.asiaa.sinica.edu.tw/meeting/20131118/

The 18th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun9 - 13 June 2014 Flagstaff, Arizona, USAhttp://www2.lowell.edu/workshops/coolstars18/

Living Together: Planets, Stellar Binaries and Stars with Planets8 - 12 September 2014 Litomysl Castle, Litomysl, Czech Republicno web site yet

Towards Other Earths II. The Star-Planet Connection15 - 19 September 2014 Portugalhttp://www.astro.up.pt/toe2014

Other meetings: http://www1.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/meetings/

57

Short Announcements

The 1.1 mm Bolocam Galactic Plane Survey version 2 data are availableAdam Ginsburg and the BGPS team

Department of Astrophysical and Planetary SciencesUniversity of Colorado, Boulder USA, 80309

E-mail contact: Adam.Ginsburg at colorado.edu

A new version of the Bolocam Galactic Plane Survey data, v2, has been released and is available through the InfraredScience Archive (IRSA) at the Infrared Processing and Analysis Center (IPAC):http://irsa.ipac.caltech.edu/data/BOLOCAM_GPS/

The new images have improved fidelity and more uniform noise. The observed area includes all data in the original v1release and some additional regions in the outer Galaxy. The new regions in the BGPS v2 include: M17, IRAS 22172,a significant expansion in l and b around the l=110 region, Mon R2, NGC 2264, parts of the Orion A and B clouds,Sharpless 235, and scattered IRAS+CO selected fields at longitude 119, 123, 126, 129, 154, 169, 181, 182, 195, 201,and 217. IRSA provides a coverage map.

There is a new catalog associated with the v2 images. The sources were extracted using Bolocat with parametersset identically as for the v1 catalog. There are sources in v1 that are not in v2 and vice-versa. These discrepanciesoccur primarily at low signal-to-noise, and objects in both catalogs are likely to be real. The v2 catalog has about a75differences will be explored in more detail in a forthcoming paper.

The flux calibration offset identified in the v1 data is now understood. The v2 data are brighter, on average, byapproximately a factor 1.5, but the factor varies from source to source. The v2 catalog should be used instead of thev1 catalog. The source of the error was the incorrect application of a flux calibration solution.

The BGPS project is supported by the National Science Foundation through NSF grant AST-0708403. J.A. wassupported by a Jansky Fellowship from the National Radio Astronomy Observatory (NRAO). The first observing runsfor BGPS were supported by travel funds provided by NRAO. Team support was provided in part by NSF grantAST-0607793 to the University of Texas at Austin.

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