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

No. 269 — 12 May 2015 Editor: Bo Reipurth (reipurth@ifa.hawaii.edu)

The Star Formation Newsletter

Editor: Bo Reipurthreipurth@ifa.hawaii.edu

Technical Editor: Eli Bressertebressert@gmail.com

Technical Assistant: Hsi-Wei Yenhwyen@asiaa.sinica.edu.tw

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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Abstracts of Newly Accepted Papers . . . . . . . . . . 17

New Jobs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Meetings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Summary of Upcoming Meetings . . . . . . . . . . . . . 46

Short Announcements . . . . . . . . . . . . . . . . . . . . . . . . 48

Cover Picture

The HII region on the cover is known as Sharp-less 171, or W1, or NGC 7822. The young clusterBerkeley 59, seen in the upper left corner, containsa group of OB-stars at a distance of∼845 pc. Thecluster is sculpting the neutral gas into cometaryclouds and elephant trunks. North is left and eastis down in this image.

Image courtesy Neil Fleminghttp://flemingastrophotography.com

Submitting your abstracts

Latex macros for submitting abstractsand dissertation abstracts (by e-mail toreipurth@ifa.hawaii.edu) 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

Frank Shuin conversation with Bo Reipurth

Q: The Lin-Shu density wave theory for the spiral struc-

ture of disk galaxies was published in 1964. What was the

genesis of this enormously influential concept?

A: The project started when C. C. Lin of MIT spent a sab-batical year in 1961 at the Institute for Advanced Studyin Princeton, to work with C. N. Yang on the theory ofsuperfluids. Lin attended a symposium on the spiral struc-ture of disk galaxies organized by Bengt Stromgren, whowas then the Professor of Astrophysics at the IAS. At thismeeting, Jan Oort gave the plenary lecture on the wind-ing dilemma of material spiral arms. Per Olof Lindblad,the son of Bertil Lindblad (for whom Lindblad resonancesare named), presented some early numerical N -body sim-ulations of a system of self-gravitating stars in a flattenedgeometry. The idealized system exhibited transient spi-ral patterns that sporadically formed and dissolved. Fromthose two lectures, Lin got the seminal idea that the spiralpatterns were really a wave phenomena, and not materialarms.

When Lin returned to MIT, he started to organize a teamof young theorists to help him develop this idea. Thegroup grew eventually to include Alar Toomre, Chris Hunter,Chi Yuan, Bill Roberts, James Mark, Y. Y. Lau, andGuiseppe Bertin. I was then a MIT physics undergraduatemajor, uncertain about how to have a career in science.Lin hired me as a summer research assistant to help himperform some numerical calculations on the problem ofwind-driven ocean circulation, another scientific problemthat interested him at the time. After spending a sum-mer crunching numbers on an old mechanical calculator,I managed to finish the assigned calculations well enoughthat Lin agreed to be my adviser for the senior thesis thatall MIT physics students had to write before graduation.This thesis was on density wave theory, and my primaryjob was to calculate asymptotically the gravitational po-

tential of a small-amplitude density perturbation, in starsor gas, in a flattened axisymmetric galaxy. The perturba-tions were oscillatory in time and had a m-fold sinusoidalvariation in azimuthal angle, with the radial variation tobe determined self-consistently from the joint equationsof dynamics for the stars and gas plus Newton’s theory ofgravity.

These calculations, supervised by Lin’s sure vision thatthe actual phenomenon had to be quasi-stationary andnot transitory, grew to become the foundations of modernspiral density-wave theory. It was pure dumb luck thatbrought me there for the beginning, but density-wave the-ory holds a special place in my heart. It is a topic to whichI have returned many times in my career, as the ideasturned out to have important applications not only indisk galaxies (e.g., the study of flocculence resulting fromthe chaos induced by overlapping subharmonic resonanceswith Greg Laughlin and Sukanya Chakrabarti, and ”feath-ering” as a parasitic instability behind self-gravitating,magnetohydrodynamic spiral shocks with Wing Kit Lee),but also in planetary rings (resonantly driven, linear andnonlinear, density waves with Jack Lissauer, Luke Dones,Jeff Cuzzi, and Chi Yuan), and in heavy protoplanetarydisks (e.g., m =1 SLING instability for binary and giantplanet formation with Scott Tremaine, Fred Adams, andSteve Ruden).

Q: From the linear theory of density wave theory of the

stars you began to study the nonlinear theory of the re-

sponse of the interstellar medium and its implications for

star formation. What influenced you to change your fo-

cus, given that there were major unresolved issues with the

stellar theory?

A: After getting my PhD from Harvard in 1968, I spentfive years on the faculty at Stony Brook, which was justgetting started with a newly formed astronomy group headedby Steve Strom. From Steve, I learned a lot about starsas points of light and not just as points of mass. I hadbecome interested in the problem of OB star formationbehind the two-armed shockwave patterns in spiral galax-ies and was collaborating with Chi Yuan and Bill Robertsfor a better astrophysical understanding of the triggeringmechanism. It soon became clear that we had to havea much better model for the interstellar medium thanthe adopted default of a single-phase isothermal gas, soI went to Berkeley on a one-semester sabbatical to learnabout the elegant two-phase model that had been devel-oped by George Field, Don Goldsmith, and Harm Habing.Together with Vinny Milione, Don Goldsmith (whom Ihelped later to recruit to Stony Brook), Chi Yuan, BillGebel, and Bill Roberts, we wrote a paper that dealt withthe problems of phase transformations and star formationin a two-phase ISM periodically exposed to shockwaves ina spiral galaxy.

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This work drew the interest of Ron Allen, who then headeda radio group at Groningen building 21cm-line receiversfor the newly commissioned Westerbork Radio SynthesisTelescope. Ron wanted to learn howWRST might be usedto test density wave theory in the context of the responseof the interstellar medium, and he came to MIT (whereI was visiting) to question C. C. Lin and me about thisproblem. Ron later asked me to go for an extended visitat Groningen, an invitation that I accepted in the summerof 1973. It was the first time that my wife Helen and Ihad spent appreciable time living in Europe, a wonderfulexperience that we both still cherish. It was also a valu-able learning opportunity for me, as a theorist, to interactclosely with radio astronomers of the caliber of Ron Allen,Ron Ekers, Miller Goss, and Renzo Sancisi, who were allat Groningen at the time. They taught me up close thevalue of checking beautiful theoretical ideas with the hardempirical facts from observations.

Q From density wave theory of the interstellar medium,

you then began to study the internal structure of contact

binaries. What initiated such a major change of research

direction?

The change was triggered by my move to Berkeley. WhileI was there on sabbatical in Fall 1971, George Field an-nounced that he was moving to Cambridge, Masssachusettsto head the joint astronomy effort at Harvard and theSmithsonian Astrophysical Observatory. The revampedorganization changed its name to the Center for Astro-physics under his leadership. The contacts I had madein the Berkeley Astronomy department encouraged me toapply for the position vacated by Field’s departure. I suc-ceeded in the application, and in the Fall of 1973, afterspending the summer in Groningen, Helen and I droveacross the USA to begin our new life at Berkeley.

My first PhD student there was Steve Lubow, a studentof the Physics Department at Berkeley, and he wanted towork on a clean problem that could make use of his amplemathematical abilities. At the time, interacting binarystars were the rage because of the tremendous discover-ies being made by X-ray telescopes launched into space.So we looked into the problem of interacting binaries anddiscovered a pioneering paper by Gerald Kuiper publishedin 1941 on the problem of mass-transfer in semi-detachedbinaries. Kuiper’s analysis invoked particle trajectories todo the dynamical calculations and may have been over-looked for that reason since the mass-transfer rates are solarge that collisions among the individual atoms makingup the mass-transfer stream must be important. My ex-perience in stellar dynamics and gas dynamics taught methe differences and similarities between collisionless andcollisional systems, which was a perfect match with SteveLubow’s expertise in doing perturbational calculations us-ing asymptotic methods. In 1975 and 1976, we wrote two

papers on the subject of mass transfer in semi-detachedbinaries that are still considered benchmarks in the field.

From semi-detached binaries to contact binaries was asmall step seemingly. But in semi-detached binaries, allthe action is at the surface or outside the stars and canbe observed. In contact binaries, all the important ac-tion is inside the stars, or within a common envelope, andcannot be observed (or so we thought). A naive idea forthe structure of contact binaries is simply to jam two sin-gle stars together. This idea leads to the conclusion thattwo main-sequence stars cannot form a co-rotating con-tact binary because their mass-radius relationships on themain-sequence are inappropriate for them both to fill theirRoche lobes except in the single case of equal-mass compo-nents. Observationally, W Ursa Majoris stars constitutethe most common form of close binary systems; the twocomponents are undoubtedly both on the main-sequence;they are co-rotating; yet no W UMa system is known thathas equal mass components! Clearly, the naive theory isinadequate, and some drastic new ingredient needs to beadded. Leon Lucy and others turned out to have very dif-ferent thoughts on what drastic new idea was needed thanSteve Lubow and I. These differences led to enormous con-troversy, not between Lucy and us, but with peripheralcritics on the scene, that has not been settled even today.

Lawrence Anderson (who then had an office next to mine),Mal Raff, and I developed a technique of Doppler imagingof W UMa stars that we never followed up after our ini-tial observational data taken at Lick Observatory becausemoving starspots badly contaminated the spectral shapeof a line that should have ideally reproduced the spatialshape of a uniformly rotating dumbbell. Had I been inthe mood to think more calmly at the time, I might haverealized that the technique offered a chance to view thedifferential internal circulation that we had postulated tobe at the heart of the resolution of the problem, but thatseemed inaccessible to observation. Somebody needs torevisit this problem and technique, which I liken to be-ing related to the theory of single stars in the same waythat diatomic molecules are related to the theory of singleatoms. In astronomy, we have a well-established theory ofsingle atoms, but none for diatomic molecules.

Q: In 1977 you published your study on self-similar col-

lapse of isothermal spheres. This was again a major change

of subject. From where came your interest in protostars?

A: The impetus came from two different directions. First,I had always been interested in how stars formed in thecontext of OB stars being the delineators of optical andUV spiral structure in disk galaxies. Second, by 1977, Iwas very upset by the tone of the debate on contact bina-ries. When I complained about the unpleasant situationprivately to Steve Strom and Bart Bok in a visit to KittPeak, both of them, separately and independently, advised

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me to switch fields – to the subject of star formation, notfrom the point of view of the interstellar medium, butfrom the point of view of the actual objects. Since Bokand Strom were my lifelong friends and mentors, I tooktheir suggestions seriously and began to study in earnestthe literature on protostars.

I knew about the controversy between Hayashi and Larsonconcerning where pre-main-sequence stars would appearin the H-R diagram after a phase of rapid gravitationalcollapse lasting on the order of 105 yr, but it was notuntil I found the papers by Larson and Penston on self-similar collapse that I saw a way in which I might makea contribution to the problem. The L-P solutions, ap-plied to gravitational collapse, correspond to states thatare initially far from equilibrium. For example, they hadsupersonic inflow toward the center at infinity. I couldnot imagine how such a state could be set up by naturalprocesses occurring in the ISM (but later, Susana Lizano,Daniele Galli, Jorge Canto, and I found a way to use re-versed L-P solutions for modeling the champagne flows ofH II regions). On the other hand, I knew from our workusing Bonnor-Ebert spheres and their cousins in the two-phase model of the ISM that such objects became singularisothermal spheres in the limit of high central concentra-tion. Thus, I was motivated to study the problem of howan unstable equilibrium starting with a singular isother-mal sphere would gravitationally collapse. To my delight,the inside-out collapse is exactly self-similar without hav-ing to assume self-similarity as a hypothesis, and the cen-tral product is a point that had a mass which grew linearlywith time! By then, I had enough experience as a real as-tronomer to realize it was important to compute also howmuch light such a point would generate as a protostar.This became the starting point of my studies with SteveStahler and Ron Taam that led to a satisfactory resolu-tion of the controversy between Hayashi and Larson, inagreement with contemporaneous numerical simulationsby Winkler and Newman.

The self-similar collapse of singular isothermal spheres wasalso the beginning of a long series of fun generalizationsthat allowed us to find analytical or semi-analytical solu-tions when we added rotation (with Susan Terebey andPat Cassen), departures from axial symmetry (DanieleGalli and Susana Lizano), magnetic fields (Zhi-Yun Liand then Fred Adams), combined rotation and magneticfields (Tony Allen, Zhi-Yun Li, Daniele Galli, and SusanaLizano), and general relativity (Mike Cai). Looking at theimplied spectral energy distributions of the correspondingcollapsing objects led Fred Adams, Charlie Lada, and meto our classification of Class I, II, and III objects basedon the appearance of their SEDs. (Later Phillipe Andreand his colleagues added a Class 0, to which I objectednot so much because it is not a valid scientific addition,

but because Roman numerals do not have a zero. Thatwas an invention of Indian and Chinese mathematicians!)

Q: In 1987, you and Fred Adams and Susana Lizano pub-

lished an ARAA review on star formation in molecular

clouds. With about 2000 citations, this is one of the most

influential articles ever in the field of star formation. What

accounts for this profound impact?

A: My guess is that the article satisfied a need from bothobservers and theorists to have a comprehensive discussionthat unified what had previously been regarded as distinctsubfields. Fred, Susana, and I synthesized the work doneat Berkeley (which included the optical/infrared observa-tions of Len Kuhi, Gibor Basri, and Martin Cohen, aswell as the radio work of Jack Welch, Dick Plambeck, MelWright, and Carl Heiles), together with the rich varietyof work done at the Center for Star Formation Studiesthat included UC Santa Cruz and NASA Ames (with toomany names to mention individually), and other organi-zations (such as by the strong star formation group at theCfA). Rightly or wrongly, we offered a rational organizingframework that (a) linked the theory and observations,and (b) gave an outline of future directions where addi-tional progress might be made. The most important con-cept that we put forward in a single cartoon is the ideathat star formation occurs in four stages: a first stage thatinvolves the formation of molecular cloud cores (e.g., My-ers and Benson); a second stage that involves the gravita-tional collapse of an unstable, slowly rotating, core to forma protostar, an infalling envelope, and a centrifugally sup-ported circumstellar disk (e.g., Sargent and Beckwith); athird stage in which the infall would be reversed by a bipo-lar outflow (e.g., Snell, Loren, and Plambeck or Rodrıguez,Ho, and Moran); followed by a fourth stage in which a pre-main-sequence star emerges surrounded by a circumstellardisk that might give birth to a planetary system.

Although we were criticized at the time for focusing onthe problem of the formation of single stars (mostly of lowmass), and not discussing much the issue of the formationof binary or multiple stars or clusters, nor emphasizingthe importance of interstellar turbulence, I still think wemade the right decision. Concrete progress in science isnot made by attacking all important problems simultane-ously: for example in quantum mechanics, one must learnto solve the hydrogen atom, and then one can move todiatomic molecules, triatomic molecules, and eventuallyDNA.

Q: In the nineties you and your collaborators developed

a detailed theory of the magnetocentrifugally driven flows

from a young magnetized star and its accretion disk, which

has had a major influence on the way we understand young

stars and their mass loss. How did this concept develop?

A: Again, it was a matter of paying attention to what the

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observers were saying, and then sieving through the dif-ferent ideas put forward by theorists, without being preju-

diced by the motivation to explain the most striking obser-

vational fact, which were frankly the beautiful images that

you, Hans Zinnecker, and others were making of jets from

YSOs and their associated, rapidly moving, Herbig-Haro

objects. For my own part, I have always preferred mo-tivation by fundamental theoretical issues to being over-influenced at the start by observational data. From thestart of discussions of pioneers in the field like LymanSpitzer and Leon Mestel, these issues have concerned theobstacles to star formation presented by rotation and mag-netic fields.

While rotation by itself could and would give rise to pro-tostellar disks, it cannot solve the angular momentumproblem of the central object. Processes like spiral den-sity waves might help transport angular momentum in theouter disk, but they become ineffective in the central re-gions. In these regions, it almost certainly must be mag-netic fields, combined with rotation, that would give riseto the bipolar outflows that act as the process by whichprotostars reveal themselves as optically visible objects.The efficacy of the combination of strong magnetic fieldscoupled with rapid rotation for producing massive out-flows was realized by early workers like Lee Hartmann andKeith MacGregor building on work by Leon Mestel con-cerning mass loss from rotating magnetized stars, or RalphPudritz and Colin Norman building on the work of RogerBlandford and David Payne on extragalactic radio jets.As a byproduct, we conjectured that the outflow processwould help a star to define its own mass – another theo-retical conundrum since molecular clouds and even theircores do not have stellar masses as a natural characteristicmass scale.

Once one has this motivation, discovering the right setof equations to solve is relatively easy (in fact, a litera-ture search showed that the appropriate formulation hadalready been given by a physics MIT professor, Stan Ol-bert, who taught me E&M), and then it was just a matterof time to find a way to solve the posed problem in a com-pletely satisfactory way (which took ten years, and thehelp of five graduate students – Joan Najita, Eve Ostriker,Sienny Shang, Mike Cai, and Subu Mohanty).

In the meantime, we discovered that by considering theheating and cooling of such outflows, a subject on whichwe had the help of Steve Ruden and Al Glassgold, we gotas a gratifying bonus the (seemingly) highly collimated,pencil-beam jets that you and others were, rightly, so ex-cited about!

Q: More recently your interest turned to chondrules. Do

studies of present-day star formation and of the distant

formation of the solar system illuminate each other?

A: The study of chondrules and calcium-aluminum-richinclusions (CAIs) came from another old scientific friend-ship: this time with Typhoon Lee, the discoverer, withJerry Wasserburg, of Al-26 in the Allende meteorite. Ty-phoon was the person who persuaded me to help bringastronomy to a higher level in Taiwan, and I helped topersuade other Chinese-American astronomers includingChi Yuan, Fred Lo, Paul Ho, Sun Kwok, Ron Taam, You-Hua Chu, and many others to lead this effort and makeit a success. But the founding and nurturing of ASIAA isanother story.

Carbonaceous chondrites like Allende are a curious mix-ture of a grainy matrix that has never experienced tem-peratures higher than 600 K if we are to judge from thefragile organic molecules that they contain, and inclusionslike chondrules and CAIs that have undergone conditionshot enough to melt rock (i.e., 2000 K or more). Yet suchmeteorites are supposed to originate from parent bodies inthe asteroid belt, which astronomical models and obser-vations suggest should never have had temperatures thatcan melt rock. CAIs also contain extinct radioactivitieslike Al-26 that are surely telling us something importantabout the early solar system, information that we have noway of accessing by remote astronomical observations.

Typhoon Lee, Sienny Shang, Al Glassgold, Mathieu Gounelle,Ernest Rehm, and I had the simple idea that the curiousmixture of hot and cold rocks may literally be a mixturebeginning with hot rocks from the interior of the primi-tive solar nebula flung out to large distances by an X-windresponsible for an ancient bipolar outflow in the solar sys-tem. The entrained material would undergo aerodynamicsize sorting in flight, with mm-sized and larger objectslanding typically in the asteroid belt, where they wouldseed the cold matrix of protoplanetary dust already therewith a sprinkling of chondrules and CAIs (which can makeup a major portion of the total mass of chondritic mete-orites). If this were the case, then we need not invent otherexotic mechanisms that would modify or completely dam-age current promising ideas about how the parent bodiesof chondiritc meteorites, i.e., planetesimals, originate (e.g.,work by Andrew Youdin and collaborators).

To minimize the number of adjustable parameters in thistheory, we tried to explain the wild variety of extinct ra-dioactivities – Al-26, Mn-53, Ca-41, Be-10, etc., that onefinds in the CAIs of carbonaceous chondrites as productsof irradiation by ancient solar flares before such materialbecame entrained and flung out to interplanetary (and in-terstellar) distances by the X-wind. This effort had mixedsuccess (to make a bad pun), as we admitted in our papers.

However, we did make a spectacularly successful predic-tion, which is that cometary material, which was thenthought to be pristine, when collected and brought backto Earth, should also contain chondrules and CAIs, but of

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smaller sizes. This prediction was borne out by the anal-ysis of Kevin McKeegan (who discovered Be-10 in CAIs)of the dust samples returned by the Stardust mission toComet Wild. Kevin has also analyzed the oxygen isotopicratios of an O-16/O-17/O-18 sample in the solar wind re-turned by the Genesis mission. They are in accord withRobert Clayton’s prediction that if X-wind theory is cor-rect, these ratios should be what are found in CAIs (whichhad previously been considered ”anomalous”) and not asthey are found on the Earth (which had previously beenconsidered ”normal”). These successful predictions do not”prove” that the origin of CAIs and chondrules by X-windtransport is true, merely that the idea has been tested byserious scientists and not found to be false.

Q: In addition to your research you have written several

textbooks, the undergraduate text book ’The Physical Uni-

verse’ and the two-volume graduate textbook ’The Physics

of Astrophysics’. What motivated such a major undertak-

ing?

A: I have always liked teaching, and I have always con-tended that there are really only two ways to learn a sub-ject well: one is to do research in it; the other is to teachit. So I have always regarded teaching not as an unwantedchore, but as an opportunity to learn about exciting de-velopments in subjects apart from my personal researchinterests. I have also always enjoyed writing, so writtenexposition comes naturally and quickly for me. Writingthe ”Physical Universe” took two years (in the days whena tremendous innovation was the invention of electric type-writers that had balls with which one could type Greekletters). Most of the two years, apart from tending mynormal duties as a Berkeley professor, was spent mak-ing revisions by the literal method of ”cut and paste.”When word processors became available on personal com-puters, it took me only one year to write the two-volumesof ”The Physics of Astrophysics.” But part of this effi-ciency derived from my always keeping complete writtennotes whenever I taught such courses at Stony Brook andBerkeley.

I have now retired three times (from Berkeley, from TsingHua, and from UC San Diego); if I ever retire permanently,I will go back to writing textbooks. I have two-thirds ofa book written entitled ”The Story of Astronomy” that Iam itching to finish when I free up some time from moreurgent tasks.

Q: Upon retirement from the University of California you

have devoted your time to studying a range of energy issues

in Taiwan. What are your goals?

A: My generation of scientists has been acutely aware ofthe global energy problem since the first Oil Crisis of 1973.And since 1982, I have had a growing concern about thethreat posed to civilization by climate change. However, I

always thought that science and technology would rise tothe two connected challenges and solve the problem beforeit got really bad. Three to four decades passed, and theproblem is still not close to being solved.

As a senior scientist with some influence in Taiwan, I fi-nally felt that I had a social responsibility to not onlygive advice, but to roll up my sleeves and try to helpfind practical solutions. Thus, I retired from the Univer-sity of California in 2009 and started a research groupusing high-temperature molten salts to advance two tech-nologies: supertorrefaction and thorium breeder reactors.(Videos of our projects on ”biochar” and ”modular tho-rium reactors” can be found on the YouTube website of”Raw Science”.) With biochar produced at rates achiev-able with supertorrefaction using waste biomass resourcesthat do not impact on food production, we estimate thatit should be possible to reverse climate change in about 40years (i.e., get CO2 concentrations in the atmosphere backdown to 350 ppm). However, this reversal is possible onlyafter other technologies bring the net CO2 emission fromall primary sources of energy generation down to zero.

To help reach the target of zero emissions, many peo-ple (including James Hansen and Bill Gates) believe thatsafer, superior (in cost), securer (in terms of weaponsproliferation), and sustainable forms of nuclear powerneed to be developed and deployed. I am betting my lasthurrah in scientific research that molten salt breeder reac-tors that run on the thorium cycle can be that reactor.

When I feel confident that these two projects can reachsuccessful completion without my continued active partic-ipation, perhaps I can really retire and finish writing ”TheStory of Astronomy.”

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My Favorite ObjectEX Lupi

Agnes Kospal

1 Episodic Accretion

The inherent variability of pre-main sequence stars mayhave multiple reasons, including time dependent mass ac-cretion from the disk. There are young stars which exhibitextreme, 1–3 orders of magnitude changes in the accre-tion rate, manifesting in sudden brightenings or “erup-tions” (Herbig 1977). My favourite object, EX Lup, isthe prototype of one of the two classes of young erup-tive stars (Fig. 1). EXors, named after EX Lup, showoutbursts often reaching 5-6 mag at optical wavelengths,although the increasing flux can be observed in the wholeoptical–infrared domain. The eruptions typically last afew months, and are repetitive on timescales from a fewyears to several decades (Herbig 2007). In many respects,these events resemble more the powerful outbursts of theFU Orionis-type stars (FUors) than the continuous bright-ness fluctuations of even the most active T Tauri stars, andit is believed that some kind of instability is needed to ex-plain the transitition from the low to the high accretionstate.

2 The large outburst in 2008

After a large 5mag flare-up in 1955-56, EX Lup had beenmostly quiescent with smaller (1-1.5mag) irregular activ-ity periods until 2008, when it went into outburst again. Anew eruption was discovered by Albert Jones, an amateurastronomer from New Zealand, who made thousands of vi-sual brightness estimates of EX Lup (among other stars)between 1954 and 2010. He published an Astronomer’sTelegram stating that EX Lup became “brighter than at

any known time since its outburst around 1955” (Jones2008). This brought EX Lup into the center of attentionand the subject of many different kinds of observations, us-ing the most modern instrumentation. It literally becamea laboratory where the accretion process in a young stellarobject could be studied with exceptional clarity. In the fol-lowing I will summarize what we learned about EX Lup,mostly based on those 10+ papers (and still counting),partly from our group, that has been published since.

2.1 The quiescent system

EX Lup is a young (1-3 Myr) low-mass (<0.6 M⊙) M0V-type star (Gras-Velazquez & Ray 2005), with a quiescentbolometric luminosity of 0.7 L⊙. Its infrared excess abovethe stellar photosphere indicates the presence of circum-stellar material. Sipos et al. (2009) modeled the spectralenergy distribution (SED) by a modestly flaring disk witha total mass of 0.025M⊙ and an outer radius of 150 au.Interestingly, the inner radius of the dust disk (0.2 au)is significantly larger than the dust sublimation radius(0.05 au). There is no hint for any envelope around thesystem. In quiescence the optical-infrared brightness ofthe source is slightly variable on a few days timescale,with an amplitude less than 0.3mag. The typical rate ofaccretion from the disk to the star is very low, on the orderof a few times 10−10M⊙.

These results suggest that on a large scale the quiescentEX Lup system resembles normal T Tauri stars, exceptfor its relatively large inner hole and low accretion rate,typically displayed by more evolved disks. However, theinnermost part of the system, the heart of the accretionprocess, seems unusual: the optical spectrum of EX Lup isunusually rich in emission lines, including permitted emis-sion lines typical of accreting T Tauri stars, and a largenumber of metallic lines which dominate the spectrum inoutburst (Kospal et al. 2008, Sicilia-Aguilar et al. 2012).

Figure 1: Artist’s impression of the EX Lup system.Credit: NASA/JPL-Caltech/T. Pyle (SSC).

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2.2 Accretion variability

Every few years the quiescent phase is irregularly inter-rupted by activity periods, when EX Lup brightens by1–1.5mag (e.g., in 1993–1994, Lehmann et al., 1995; orthe four smaller flare-ups between 1995 and 2005, Her-big 2007). In these periods the photospheric spectrum isveiled by a hot continuum, inverse P Cygni absorptioncomponents displaced by several hundreds of kms−1 ap-pear at the higher Balmer lines, the emission-line structureundergo striking variations, and many emission lines ex-hibit narrow and broad line profile components. Thesesignatures indicate intermittent mass infall in magneto-spheric accretion events.

Less frequently, EX Lup produces exceptionally power-ful eruptions, like its historically largest outburst in 2008,when it brightened by a factor of ∼100 in visual light. Thesource reached a peak brightness of V = 8mag in aboutfour weeks, slowly decayed in the high state for six monthswith some quasi-periodic oscillations, and returned to theinitial state within a few weeks (Fig. 2). In outburst, theaccretion rate rose to a few times 10−7M⊙, three orders ofmagnitude higher than in quiescence (Juhasz et al. 2012).

Figure 2: Visual light curve of EX Lup based on Juhaszet al. (2012) showing the extreme outburst in 2008.

2.3 Magnetospheric accretion

The modeling of the quiescent data indicated an inner holein the optically thick disk within 0.2–0.3au. This resultexcludes accretion proceeding through an equatorial accre-tion disk that approaches the stellar surface in a bound-ary layer. In outburst, the optical and near-infrared spec-tra revealed strong permitted emission lines, and metalliclines (Sicilia-Aguilar et al. 2012; Kospal et al. 2011). Thedynamics of the broad component of the emission lineprofiles suggested that they originate in a hot (6500K),dense, non-axisymmetric, and non-uniform accretion col-

umn that suffers velocity variations along the line-of-sighton timescales of days. Assuming Keplerian rotation, theemitting region would be located at ∼0.1–0.2 au, consis-tent with the location of the inner disk rim. The near-infrared hydrogen lines display a strong spectro-astrometricsignal, also suggesting a funnel flow or disk wind originrather than an equatorial boundary layer.

The picture emerging from the spectroscopic observations,both in quiescence and in outburst, is broadly consistentwith the standard magnetospheric accretion model usuallyassumed for normally accreting T Tauri stars. The rapidrecovery of the system after the outburst and the similaritybetween the pre-outburst and post-outburst states suggestthat the geometry of the accretion channels did not changebetween quiescence and outburst, only the accretion ratevaried (Sicilia-Aguilar et al. 2012).

In a magnetospheric accretion scenario, the infalling mate-rial reaches the star in hot spots. Indeed, based on the ex-tensive coverage of the outburst by ESO instruments andthe Spitzer Space Telescope, Juhasz et al. (2012) compiledan outburst SED, and identified a hot single-temperatureblackbody component which emitted 80%–100% of the to-tal accretion luminosity. In the X-ray regime, Teets etal. (2012) found a strong correlation between the decreas-ing optical and X-ray fluxes, obtained by Chandra, sug-gesting that these declines are the result of decreasing ac-cretion rate. Using XMM-Newton, Grosso et al. (2010)identified a soft X-ray spectral component that is mostlikely associated with accretion shocks. They also ob-served UV emission reminiscent of accretion events evi-dently dominated by emission from accretion hot spots.

2.4 The physics of the outburst

The 2008 outburst also provided new insight into the physicsof the outburst. Interestingly, no dedicated outburst mod-els exist for EXors in the literature. Commonly, scenar-ios developed for the more powerful FUor eruptions areinvoked, such as viscous-thermal instabilities in the disk(Bell & Lin 1994), a combination of gravitational andmagneto-rotational instability (Armitage et al. 2001), oraccretion of clumps in a gravitationally fragmenting disk(Vorobyov & Basu 2010, 2015). Yet another type of theoryinvolves a close stellar or sub-stellar companion that per-turbs the disk and triggers the onset of the enhanced accre-tion (Lodato & Clarke 2004; Bonnell & Bastien 1992). An-other model proposes that accretion onto a strongly mag-netic protostar is inherently episodic if the disk is trun-cated close to the corotation radius (D’Angelo & Spruit2010).

Decomposing the profiles of CO fundamental emission lines,Goto et al. (2011) separated the profiles of the fundamen-tal emission lines into narrow (FWHM ≈ 50 km s−1) and

9

boad (FWZI ≈ 150km s−1) components. While the for-mer is mostly constant in time and traces cool gas at acharacteristic radius of 0.4 au, the latter decays with time,and is emitted by hot gas orbiting the star at 0.04–0.4au,clearly associated with the outburst event (Fig. 3). Thisregion largely overlaps with the optically thin, dust-free,but obviously gas-rich inner part of the circumstellar disk.This result lends support to theories where the outburst isconfined to the innermost 0.4 au, without the involvementof the outer disk.

Juhasz et al. (2012) also concluded, based on argumentsinvolving the viscous timescale in the disk, that all mate-rial accreted in the 2008 outburst should have been locatedwithin 0.1 au from the central star. However, while thetriggering mechanism is probably related to accretion, it isunlikely that thermal instability, the most widely acceptedmodel of FUor outbursts, triggered EX Lup’s flare-up.

Figure 3: Schematic representation of the broad- and thenarrow-line emitting regions from Goto et al. (2011).

2.5 Effects of the outburst on the circum-stellar environment

The 2008 eruption of EX Lup provided direct evidencesthat the outburst had a strong impact on the circumstellarenvironment. Abraham et al. (2009) studied Spitzer spec-troscopy, obtained close to peak brightness, and discoveredmid-infrared features in the outburst spectrum that werenot present in quiescence (Fig. 4). These features couldbe attributed to crystalline forsterite, and we suggestedthat the crystals were produced through thermal anneal-ing in the surface layer of the inner disk by heat from theoutburst.

Juhasz et al. (2012) presented additional multi-epoch Spitzerspectra, and showed that the strength of the crystallinebands between 8 and 30µm increased right after the end ofthe outburst, but six months later the crystallinity in the10µm silicate feature complex decreased. Modeling themid-infrared spectral evolution of EX Lup showed that,although vertical mixing in the disk would be a poten-tial explanation, fast radial transport of crystals (e.g., bya stellar/disk wind) was required. These results demon-strate that part of the material irradiated and processedby the outburst found its way to the outer disk. Thus,

episodic crystallization provides a new scenario to producethe building material for primitive comets.

Motivated by the discovery of episodic crystallization, Ban-zatti et al. (2012) looked for chemical changes possiblyinduced by the outburst, using archival Spitzer spectrabefore and during the 2008 outburst. They found remark-able changes: the H2O and OH line fluxes increased, newOH, H2, and HI transitions were detected, and organicswere no longer seen. These results demonstrate that theoutburst affected not only the surface mineralogy, but alsothe chemistry in the inner disk.

Figure 4: The spectrum of EX Lup in 2005 (left) and in2008 (right), based on Abraham et al. (2009). The verti-cal blue dash at 9.7µm corresponds to the peak of wave-length of the amorphous silicate profile. Peak wavelengthsof forsterite at 10.0 and 11.2µm are marked by red dashes.The grey curve displays the emissivity of pure forsterite.

2.6 Brown dwarf companion or accretioncolumns?

An interesting result arose from a five-year radial velocitysurvey of EX Lup, collecting 54 observations with HARPSand FEROS (Kospal et al. 2014). We found that the ra-dial velocity of EX Lup is periodic (P = 7.417d), with sta-ble period, semi-amplitude (2.2 km s−1), and phase over atleast four years of observations. This period is not presentin any of the usually invoked activity indicators. The ob-served absorption line radial velocities can be fitted witha Keplerian solution around a 0.6M⊙ central star with msin i = (14.7 ± 0.7) MJup and eccentricity of e = 0.24(Fig. 5). No classical cold or hot stellar spot can explainthe observations (they would predict too high photomet-ric variability). If confirmed, the companion’s mass wouldfall into the brown dwarf desert, which, together with theunusually small separation of 0.06 au would make EXLupa unique binary system, with interesting implications onthe physical mechanisms responsible for triggering the out-

10

burst.

Interestingly, the emission lines of EXLup also show aperiodic signature with the same period. This suggestsvery stable accretion columns, and the rotational modula-tion of the emission lines originating close to the accretionshock above the stellar surface. Constructing a model thatwould satisfactorily explain the radial velocity variationsof both the absorption and emission lines, either with orwithout a companion, is under way (Sicilia-Aguilar et al.,submitted).

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Figure 5: Best Keplerian fit to the absorption line radialvelocities of EX Lup. The different colors indicate differentobserving seasons. The middle panels shows the residuals,while the bottom panel displays the radial velocity of theemission lines.

3 Outlook

The eruptive phenomenon in young stars is a fundamentalprocess during star formation. At the earliest phases, ithelps building up the final mass of the star, and offers apossible solution for the luminosity problem of protostarsas well. At later phases, when EXor outbursts possiblyhave a dominant role, the eruptions have a marked ef-fect on the inner disk properties, strongly influencing theinitial conditions for the formation of terrestrial planets.The 2008 outburst of EX Lup provided a pioneering ex-periment in this field.

The freshly created silicate crystals could be used as trac-ers of vertical and radial motions in the disk. In 1955–56EX Lup underwent an outburst of similar strength andlikely produced a similar amount of crystals than in 2008,

but in 2005 there were no crystalline signatures in themid-infrared spectrum. The disappearance of the crystalsmay indicate vertical mixing in the disk bringing up freshunprocessed material to the surface, and/or radial trans-port outward. Following the temporal changes of the crys-talline features during the next years/decades will provideotherwise inaccessible dynamical information on the disk.How a perturbed system relaxes to equilibrium specifiesthe timescales of the relevant physical processes. A de-tailed theoretical investigation of the 2008 outburst mayalso be a milestone in understanding the physics of theeruptive phenomenon. Due to the focused campaigns us-ing many top instruments, the 2008 outburst is probablythe best documented one in history, and thus offers thehighest chance to discriminate among the possible physi-cal scenarios and the relative importance of different kindsof instabilities in the process.

I believe that while astronomy extensively uses a statisti-cal approach, very detailed studies of individual objects,especially the prototypes of certain classes of objects, isanother promising way towards a thorough understand-ing of the physics in question. EX Lup is an exceptionalobject, and its future observations may still provide break-throughs in understanding the eruptive phenomenon. Theonly sad point is that we cannot rely on the late AlbertJones to announce the next large outburst. I know thathe was proud to have discovered both large eruptions ofEX Lup, in 1955 and 2008, and I would like to acknowl-edge here his memorable contribution to the work on myfavourite object. I would like to thank the efforts of all myEX Lup-enthusiast collaborators as well: it has been andstill is a pleasure to work with you. Acknowledgement isdue also to the support by the Momentum grant of theMTA CSFK Lendulet Disk Research Group.

References:

Abraham et al. 2009, Nature, 459, 224

Armitage et al. 2001, MNRAS, 324, 705

Banzatti et al. 2012, ApJ, 745, 90

Bell & Lin 1994, ApJ, 427, 987

Bonnell & Bastien 1992, ApJ, 401, L31

D’Andelo & Spruit 2010, MNRAS, 406, 1208

Goto et al. 2011, ApJ 728, 5

Gras-Velazquez & Ray 2005, A&A, 443, 541

Grosso et al. 2010, A&A, 522, 56

Herbig 1977, ApJ, 217, 693

Herbig 2007, AJ, 133, 2679

Jones 2008, CBET, 1217, 1

Juhasz et al. 2012, ApJ 744, 118

Kospal et al. 2008, IBVS, 5819, 1

Kospal et al. 2011, ApJ 736, 72

Kospal et al. 2014, A&A, 561, A61

Lehmann et al. 1995, A&A, 300, L9

Lodato & Clarke 2004, MNRAS, 353, 841

Sicilia-Aguilar et al. 2012, A&A, 544, A93

Sipos et al. 2009, A&A, 507, 881

Teets et al. 2012, ApJ, 760, 89

Vorobyov & Basu, 2010, ApJ, 719, 1896

Vorobyov & Basu, 2015, arXiv:1503.07888

11

Perspective

The role of ices in star andplanet formationKlaus Pontoppidan

Interstellar ices: Esoteric or fundamental?

I have always thought that ices in inter- and circumstellarenvironments were incredibly fascinating. Astrophysicalices is a microworld that incorporates disciplines not oftenassociated with astronomy, including surface chemistryand material sciences. In dense, cold molecular clouds, aswell as in protostellar envelopes much, or even most, of thecarbon, oxygen and nitrogen are frozen on refractory dustgrains as simple, volatile molecules. The most abundantspecies are generally water, CO2 and CO, but a greaternumber of various organics are also known. Ices are essen-tial reservoirs of carbon, oxygen and nitrogen in molecularclouds and protostellar envelopes, but also in protoplan-etary disks. They played a key role in forming our solarsystem and determining its composition, and likely playa similar role for exoplanets. However, it is very hardto observe and characterize ice in protoplanetary disks,although we know it is there (Pontoppidan et al. 2005;Honda et al. 2009). Most recently, McClure et al. (2015)used Herschel to detect ice in emission in a small numberof protoplanetary disks using the far-infrared 60µm bandof crystalline water ice. On the other hand, it is far easierto observe ices in dense molecular clouds and protostellarenvelopes. Consequently, most of our empirical under-standing of ices, their distribution and physical chemistrycomes from studies of interstellar ice in star-forming re-gions.

Our observational knowledge of interstellar ices is domi-nated by spectroscopic surveys with the VLT, Keck, Spitzer,

and most recently, AKARI. The dominant technique is in-frared absorption spectroscopy toward both young stars aswell as Galactic background stars located far behind thecloud material of interest (Oberg et al. 2011). A typi-cal mid-infrared spectrum of ices in a protostellar enve-lope is shown in Figure 1. Additional, indirect informa-tion has been obtained using rotational spectroscopy oforganics in protostars, thought to trace evaporating ices.Boogert, Gerakines & Whittet (2015) present a compre-hensive review of observations of interstellar ices. In themid- to late 90s, the Infrared Space Observatory offeredthe first detailed look at ices covering nearly the full rele-vant wavelength range, but only for the brightest, mostlymassive young stellar objects. This was followed by lessbiased ground-based surveys of water and CO ices in the3-5µm region, and then by a treasure trove of Spitzerspectroscopy in the 5–37µm region, albeit at relativelylow spectral resolution that did not fully resolve all icefeatures.

Yet, the study of interstellar ices is not naturally pop-ular within the broad astronomical community. Somemay think of it as a somewhat esoteric endeavor withfew implications for general astrophysics. Figure 2 showsthe rates of astronomy publications on ices, created usingADS Labs. Two different rates are shown. One search-ing for papers on observations of ices, combining ice key-words with names of observatories and instruments withmid-infrared spectroscopic capabilities. The other showsstudies of interstellar ices using models and laboratoryexperiments. Only a couple of hundred refereed papershave ever been produced on observations of ices. Theypeaked during and immediately after the ESA InfraredSpace Observatory mission, although Spitzer maintaineda steady rate of observational publications of roughly 7 ayear until 2013. In contrast, publications using theoreticalmodels or laboratory experiments have been steadily in-creasing, and now appear at a rate ∼ 3 times higher thanthat of observational papers. This may indicate that thefield is lacking in astronomical data and facilities that canproduce them efficiently, while the laboratory astrochem-istry/physics community is eager to contribute. With thisessay, I present some of the reasons why ices are importantand exciting, and why we can expect the field to grow inthe future.

The Galactic ice reservoir

A large reservoir of water in the Milky Way galaxy ex-ists in the form of mantles covering sub-micron-sized dustgrains in dense molecular clouds. Water ice appears indense clouds once the extinction through the cloud (twosurfaces) passes above a certain observational threshold of3-5mag (Chiar et al. 1995; Boogert et al. 2013). Since

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Figure 1: The ice bands toward the prototypical solar-mass young stellar object HH46 IRS. The infrared source towardwhich the ice spectrum is taken, and which drives a large outflow, is hidden behind a dense protostellar envelope tothe far left of the optical image. The spectra are from VLT-ISAAC and Spitzer (Pontoppidan et al. 2003; the c2dsurvey, Evans et al. 2003; the Cornell Atlas of Spitzer IRS sources, Lebouteiller et al. 2011). The background imageis from the Hubble Space Telescope; NASA, ESA and Hartigan et al. 2011.

about 75% of the mass of molecular clouds can be found in-side this threshold (Cambresy et al. 2002), and the abun-dance of water ice relative to elemental hydrogen is ratherwell established as ∼ 2 − 10 × 10−5 (Pontoppidan et al.2004; Whittet 2010), we can estimate the total mass ofwater in molecular cloud ices in the galaxy. If the MilkyWay molecular gas mass is 109M⊙, the Milky Way waterice mass is ∼ 4× 104M⊙. A comparatively small amountof water may be found in cool stellar atmospheres. Incomparison, the Oort cloud has been estimated to containa few tenths of an Earth mass of water ice (Kaib & Quinn2009; Weissman 1983), with the Kuiper belt contributinga somewhat smaller fraction of ice mass (Luu & Jewitt2002). If we disregard the ice that was incorporated intogiant planet cores, which may no longer be in the formof water, the various icy moons in the solar system con-tain another smaller fraction of an Earth mass. If mostof the 2 × 1011 stars of the Milky Way host similar icereservoirs, this translates to a total Galactic reservoir of∼ 2 × 106M⊙ of planetary water ice, almost all of it incomets. Few studies exist investigating the ice content ofexternal galaxies, but it may be a reasonable assumptionthat the same statement holds true for the local universe.Of course, we do not know whether exoplanetary systemsall contain Oort clouds of similar mass as that of the Sun,but it is interesting that the dominant reservoir of waterin the Galaxy may be sequestered in comets and other icyplanetesimals, rather than in molecular clouds. Part ofthe reason for this is that comets are long-lived ice reser-

voirs, while interstellar ices on small dust grains only per-sist as long as their parent molecular cloud, or a few Myr,unless they are accreted onto a protoplanetary disk andsequestered in planetesimals.

From simplicity to complexity

It is now generally accepted that the molecules comprisinginterstellar ices are formed by surface reactions. As was al-ready predicted by van de Hulst (1946), the most commonsurface reaction is hydrogen addition, leading to the for-mation of saturated species from atomic precursors, suchas water, CH4, NH3 (from oxygen, carbon and nitrogen,respectively).

Simple molecules act as spectroscopic probes of molecularsurfaces in laboratories, and infrared transmission spec-troscopy serves the same role for astrophysical ices. In-deed, extensive laboratory experiments have made funda-mental contributions to our understanding of interstellarices. Initially, the laboratory was used to simulate astro-physical conditions, in particular cryogenic temperatures,extremely low pressures and radiation environments, tocreate transmission spectra of ices for direct comparisonto astronomical observations (Hudgins et al. 1993; Ehren-freund et al. 1999). However, as it was realized that someastrophysical parameters can never be replicated in thelaboratory, such as astrophysical time scales of a millionyears, the emphasis on the experimental side has shifted

13

Observational publications on interstellar ices Modeling and laboratory publications on interstellar ices

Figure 2: The rate of publications discussing observations of interstellar ices (left) and modeling or laboratory studies(right). The yellow and blue columns show refereed and unrefereed publications, respectively. The figures were createdusing ADS Labs.

somewhat to improve our fundamental understanding ofthe physical chemistry governing ice formation and the in-teraction of icy mantles with light and radiation. This ap-proach yields kinetic parameters, reaction rates and the re-lation between spectroscopic band profiles and the detailedmicrostructure of the ice (Fraser et al. 2001; Collingset al. 2004; Oberg et al. 2009b). With the appropri-ate understanding of spectral signatures of ice in hand,it is remarkable, that, using a telescope equipped withan infrared spectrometer, we can in principle determinethe detailed molecular configuration of dust grains: whichmolecular species is in direct intermolecular contact withothers, whether the ices are arranged in smooth spheres orin more complex structures, etc. All of this can be accom-plished, not only in the convenient setting of a laboratory,but at distances of 100s of pc, or even in other galaxies(Spoon et al. 2003; Yamagishi et al. 2011). While the im-portance of astrophysical ices is often under-appreciatedin these times of fashionable exoplanets and dark energy,they actually play a fundamental role in many different as-pects of star and planet formation, as well as, of course, inthe pathway that carbon, oxygen, nitrogen and hydrogenonce took to become part of our own Earth’s atmosphere.

An important realization of the last decade is that in-terstellar ice mantles are highly structured and heteroge-nous at the individual dust grain level. Ice mantles growthroughout the evolution of a dense clouds and in proto-stellar envelopes beyond a few hundred AU. Conversely,desorption processes are comparatively slow, at least untilthe icy dust grains enter a protoplanetary disk, or are de-

stroyed by protostellar feedback processes, such as shocksor thermal heating. In contrast to pure gas-phase chem-istry, which is locally well mixed, and often in chemi-cal equilibrium, ice mantles are generally not well-mixedand their chemistry probably never reaches an equilibriumstate in the few million years they persist in the form ofsub-micron-sized grains in a molecular cloud. As a conse-quence a typical dust grain will contain a layered recordof its local thermal, chemical and radiative environment,as well as the time it spent at each stage. As alreadymentioned, we now know that water and CO2 ices formearly on as soon as the cloud is shielded from the inter-stellar radiation field by ∼ 2mag (Whittet et al. 2007).This environment corresponds to relatively low densities.CO formed by classical ion-molecule reactions in the gas-phase will only freeze-out onto dust grains at higher den-sities and corresponding extinctions. However, becausethe freeze-out time scale for a gas-phase species scales in-versely with density, provided the dust grain surfaces aresufficiently cold, it takes longer than the life time of thecloud for CO to freeze out at densities of 104. However,as densities increase to 106, CO is able to rapidly freezeout (“catastrophically”; Pontoppidan 2006; Oberg et al.2013). This leads to the formation of a layered ice with a,likely, quite homogenized mix of water and CO2, coveredby a thick layer of nearly pure CO. Initially, at the lowtemperatures typical for dense molecular clouds and cores(T ∼ 10K), these two reservoirs (often referred to as polarand apolar, with the former being the water-rich mantle)are separate and probably do not interact strongly chemi-

14

cally, even though they inhabit the same sub-micron-sizeddust grains!

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Figure 3: The early evolutionary sequence of interstellarices as it is currently understood. Starting with bare dustgrain surfaces, a thick layer of primarily water and CO2,with traces of ammonia and methane is slowly developed,likely at time scales of 105−6 yr. As the cloud density in-creases CO freezes out on much shorter time scales, 104 yror less, leading to the formation of a nearly pure CO layer.Prior to or during the formation of protostellar cores, someof the CO is converted to methanol. From Oberg et al.2011.

The upper pure CO layer may play a quite fundamen-tal role in the Universe as part of a chain of events thatultimately lead to the development of habitable worlds(planets and moons). The CO ice is exposed to interac-tions with surrounding cloud gas. In particular, this leadsto the formation of formaldehyde (H2CO) and methanol(CH3OH) by hydrogen addition (Watanabe & Kouchi 2002;Fuchs et al. 2009; Cuppen et al. 2009). Indeed, if water,ammonia and methane are the saturated surface ice ver-sions of gas-phase elemental oxygen, nitrogen and carbon,methanol is the saturated ice version of CO. It appar-ently takes some time to build up appreciable abundancesof methanol in the CO ice layer, because less evolved(younger) quiescent areas of dark clouds tend to not havedetectable methanol ice (< 1−5% relative to water; Boogertet al. 2013). Nevertheless, methanol continues to build upover time, and perhaps other factors, such as slightly en-hanced dust temperatures or increased atomic hydrogeninflux, help catalyze the process. Eventually, very highmethanol abundances of as much as 30% relative to wa-ter ice are observed in some of the densest cloud regions(the Serpens star-forming region is known to have areaswith particularly high methanol ice abundances) and insome protoplanetary envelopes (Pontoppidan et al. 2004;

Boogert et al. 2011).

Why is methanol important? As it turns out, methanolis a key ingredient for forming large amounts of com-plex organic molecules, including pre-biotic species. Thechemical pathways are likely complex, and may derive ei-ther from ice chemistry coupled with ultraviolet irradia-tion (Oberg et al. 2009a) or via gas-phase reactions cat-alyzed by evaporated methanol ice in the vicinity of hotyoung stars, as observed in hot cores (Nomura & Millar2004). These complex organic compounds can be quitestable and are likely to survive accretion onto protoplan-etary disks and to take part in the formation of plan-etesimals and planets, potentially supporting the develop-ment of life. ALMA has recently discovered such complexorganic molecules in protoplanetary disks (Oberg et al.2015).

Interstellar ices and star formation withJWST

What is the future for observations of ices in planet- andstar-formation? In the past decade, we have answeredmany questions related to ices, and revealed some of theroles it plays in the chemical evolution of circumstellarmaterial, with fundamental consequences for the initialconditions of planetary composition. But we are far fromdone. Rather, as usually happens with more data, we nowhave more questions, as well as a clearer idea of what thequestions are. One fundamental problem that we mustovercome is that remote sensing of ices has its limitations.It is incredible that we have determined the structures andenvironments of water, CO2 and CO ices, and to somedegree of methanol. However, there are many more icespecies of equal or greater importance that we have so farbeen unable to understand. Further, there are still manystrong infrared absorption bands that remain unidentified.Most ice bands are broad, so we have generally spectrallyresolved them.

The next event that will shape our understanding of in-terstellar ices will be the launch of the James Webb SpaceTelescope (JWST). With a telescope diameter 7.5 timesthat of Spitzer, and medium resolution spectroscopy ex-tending from 1 through 28µm, JWST seems like the idealmachine for observations of interstellar ices, although itwas never designed with ices in mind. While all of theJWST instruments are capabable of obtaining various typesof ice spectroscopy, two in particular stand out. NIRSpecis the near-infrared spectroscopy workhorse. It featuresthe first multi-object spectrograph capable of observing inthe, for ices, critical 3-5µm region. Using a novel micro-shutter array (MSA; Moseley et al. 2004), NIRSpec isable to obtain 3-5µm spectra of more than 100 targets si-multaneously within a 3× 3 arcminute field of view at an

15

JWST NIRSpec multi-object spectrograph field of view

Figure 4: 3.6-8.0µm color composite of the isolated darkcore BHR76 as observed by the Spitzer Cores to DisksLegacy program (Evans et al. 2003). The field of viewof the NIRSpec multi-object spectrograph on the JamesWebb Space Telescope is superimposed on the image. Thedensest part of the core is visible in absorption towarddiffuse Galactic background emission. The faintest back-ground stars visible in this image are around 15µJy at4.5µm; JWST-NIRSpec will be able to obtain ice spec-troscopy toward every single star seen in the image, aswell as many too faint to be detected by Spitzer.

average resolving power of R ∼ 2700. Reaching a spectro-scopic 10σ sensitivity of around 8µJy in 1 hour at 4.5µm,NIRSpec1 represents an astounding 5000-fold increase inraw sensitivity compared to ISAAC on the Very Largetelescope (the previous source of ice spectroscopy at com-parable resolving power).

What this means for ice observations is that JWST willbe able to efficiently and with very high spatial resolutionmap the distribution of major ice species in dense coresand even protostellar envelopes by obtaining absorptionspectroscopy toward a dense grid of background stars. Thematch of the NIRSpec multi-object field of view to typicaldense cores is illustrated in Figure 4. JWST-NIRSpec willsee the formation of water, CO2 and methanol directly, asa function of density and temperature in molecular cloudmaterial. It will be able to image the effects of energeticprocessing on cloud boundaries and by protostellar shocks,as they occur.

The other JWST instrument that will revolutionize obser-

1See http://www.stsci.edu/jwst/instruments/nirspec for

more details.

vations of interstellar ices is the mid-infrared instrument,MIRI. MIRI does not have the multiplexing of NIRSpec,but covers the critical 5-28µm wavelength region at un-precedented sensitivity and spectral resolution2. MIRIwill improve upon the Spitzer spectral resolution by a fac-tor 4 beyond 10µm and a factor 30 between 5 and 10µm.The sensitivity is improved by up to two orders of magni-tude at wavelength ranges covering critical ice species, in-cluding methane and the highly diagnostic 15.2µm bend-ing mode of CO2. It also includes the 5-8µm region, whichis filled with ice bands, many of which remain unidentified(Boogert et al. 2008). As with NIRSpec, MIRI opens up agreat expanse of discovery space for ices, allowing observa-tions in a much wider range of astrophysical environmentsthan before, from the Galactic center to the MagellanicClouds.

References:

Boogert et al. 2008, ApJ, 678, 985

Boogert et al. 2011, ApJ, 729, 92

Boogert et al. 2013, ApJ, 777, 73

Boogert, Gerakines & Whittet 2015, ARA&A, 53, in press

Cambresy et al. 2002, AJ, 123, 2559

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Abstracts of recently accepted papers

Planet formation around binary stars: Tatooine made easy

B. C. Bromley1 and S. J. Kenyon2

1 Department of Physics & Astronomy, University of Utah, 115 S 1400 E, Salt Lake City, UT, 84112, USA2 Smithsonian Astrophysical Observatory, 60 Garden St, Cambridge, MA 02138, USA

E-mail contact: bromley at physics.utah.edu

We examine characteristics of circumbinary orbits in the context of current planet formation scenarios. Analyticalperturbation theory predicts the existence of nested circumbinary orbits that are generalizations of circular pathsaround a single star. These orbits have forced eccentric motion aligned with the binary as well as higher frequencyoscillations, yet they do not cross, even in the presence of massive disks and perturbations from large planets. Forthis reason, dissipative gas and planetesimals can settle onto these ”most circular” orbits, facilitating the growth ofprotoplanets. Outside a region close to the binary where orbits are generally unstable, circumbinary planets formin much the same way as their cousins around a single star. Here, we review the theory and confirm its predictionswith a suite of representative simulations. We then consider the circumbinary planets discovered with NASA’s Keplersatellite. These Neptune- and Jupiter-size planets, or their planetesimal precursors, may have migrated inward to reachtheir observed orbits, since their current positions are outside of unstable zones caused by overlapping resonances. Insitu formation without migration seems less likely, only because the surface density of the protoplanetary disks mustbe implausibly high. Otherwise, the circumbinary environment is friendly to planet formation, and we expect thatmany Earth-like ”Tatooines” will join the growing census of circumbinary planets.

Accepted by The Astrophysical Journal

http://arxiv.org/pdf/1503.03876

The inner environment of Z CMa: High-Contrast Imaging Polarimetry with NaCo

H. Canovas1,6, S. Perez2,6, C. Dougados3, J. de Boer4,7, F. Menard3, S. Casassus2,6, M.R. Schreiber1,6,L.A. Cieza5,6, C. Caceres1,6, J.H. Girard7

1 Departamento de Fısica y Astronomıa, Universidad de Valparaıso, Valparaıso, Chile2 Departamento de Astronomıa, Universidad de Chile, Casilla 36-D, Santiago, Chile3 UMI-FCA, CNRS/INSU, France (UMI 3386), and Dept. de Astronomıa, Universidad de Chile, Santiago, Chile4 Sterrewacht Leiden, Universiteit Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands5 Facultad de Ingenierıa, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile6 Millennium Nucleus “Protoplanetary Disks in ALMA Early Science”7 European Southern Observatory, Casilla 19001, Santiago, Chile

E-mail contact: hector.canovas at dfa.uv.cl

Context. ZCMa is a binary composed of an embedded Herbig Be and an FU Ori class star separated by ∼100 au.Observational evidence indicate a complex environment in which each star has a circumstellar disk and drives a jet,and the whole system is embedded in a large dusty envelope.Aims. We aim to probe the circumbinary environment of ZCMa in the inner 400 au in scattered light.Methods. We use high contrast imaging polarimetry with VLT/NaCo at H and Ks bands.Results. The central binary is resolved in both bands. The polarized images show three bright and complex structures:a common dust envelope, a sharp extended feature previously reported in direct light, and an intriguing bright clumplocated 0.′′3 south of the binary, which appears spatially connected to the sharp extended feature.Conclusions. We detect orbital motion when compared to previous observations, and report a new outburst drivenby the Herbig star. Our observations reveal the complex inner environment of ZCMa with unprecedented detail andcontrast.

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Accepted by A&A Letter

http://arxiv.org/pdf/1504.05197

The infrared emission of young Hii regions: A Herschel/Hi-GAL study

R. Cesaroni1, M. Pestalozzi2, M. T. Beltran1, M. G. Hoare3, S. Molinari2, L. Olmi1,4, M. D. Smith5,G. S. Stringfellow6, L. Testi7,1 and M. A. Thompson8

1 INAF, Osservatorio Astrofisico di Arcetri, Italy2 INAF, Istituto di Astrofisica e Planetologia Spaziale, Italy3 School of Physics and Astrophysics, University of Leeds, UK4 University of Puerto Rico, Rio Piedras Campus, Physics Dept., Puerto Rico5 Centre for Astrophysics and Planetary Science, University of Kent, UK6 Center for Astrophysics and Space Astronomy, University of Colorado, USA7 European Southern Observatory, Garching, Germany8 Centre for Astrophysics Research, University of Hertfordshire, UK

E-mail contact: cesa at arcetri.astro.it

Investigating the relationship between radio and infrared emission of Hii regions may help shed light on the nature ofthe ionizing stars and the formation mechanism of early-type stars in general.We have taken advantage of recent unbiased surveys of the Galactic plane such as Herschel/Hi-GAL and VLA/CORNISHto study a bona-fide sample of young Hii regions, located in the Galactic longitude range 10◦–65◦, by comparing themid- and far-IR continuum emission to the radio free-free emission at 5 GHz.We have identified the Hi-GAL counterparts of 230 CORNISH Hii regions and reconstructed the spectral energy dis-tributions of 204 of these by complementing the Hi-GAL fluxes with ancillary data at longer and shorter wavelengths.Using literature data, we obtained a kinematical distance estimate for 200 Hii regions with Hi-GAL counterparts anddetermined their luminosities by integrating the emission of the corresponding spectral energy distributions. We havealso estimated the mass of the associated molecular clumps from the (sub)millimeter flux densities.Our main finding is that for ∼1/3 of the Hii regions the Lyman continuum luminosity appears to be greater thanthe value expected for a zero-age main-sequence star with the same bolometric luminosity. This result indicates thata considerable fraction of young, embedded early-type stars present a “Lyman excess” possibly due to UV photonsemitted from shocked material infalling onto the star itself and/or a circumstellar disk. Finally, by comparing thebolometric and Lyman continuum luminosities with the mass of the associated clump, we derive a star formationefficiency of 5%.The results obtained suggest that accretion may be still present during the early stages of the evolution of Hii regions,with important effects on the production of ionizing photons and thus on the circumstellar environment. More detailednumerical models describing the accretion process onto massive stars are required to shed light on the origin of theobserved Lyman excess.

Accepted by Astronomy and Astrophysics

http://www.arcetri.astro.it/science/starform/preprints/cesa_25.pdf

Early evolution of embedded clusters

J.E. Dale1,2, B. Ercolano1,2, I.A. Bonnell3

1 Excellence Cluster ‘Universe’, Boltzmannstr. 2, 85748 Garching, Germany2 Universitats–Sternwarte Munchen, Scheinerstr. 1, 81679 Munchen, Germany3 Department of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS

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

We examine the combined effects of winds and photoionizing radiation from O–type stars on embedded stellar clustersformed in model turbulent molecular clouds covering a range of masses and radii. We find that feedback is ableto increase the quantities of dense gas present, but decreases the rate and efficiency of the conversion of gas to starsrelative to control simulations in which feedback is absent. Star formation in these calculations often proceeds at a ratesubstantially slower than the freefall rate in the dense gas. This decoupling is due to the weakening of, and expulsion

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of gas from, the deepest parts of the clouds’ potential wells where most of the star formation occurs in the controlsimulations. This results in large fractions of the stellar populations in the feedback simulation becoming dissociatedfrom dense gas. However, where star formation does occur in both control and feedback simulations, it does so indense gas, so the correlation between star formation activity and dense gas is preserved. The overall dynamical effectsof feedback on the clusters are minimal, with only small fraction of stars becoming unbound, despite large quantitiesof gas being expelled from some clouds. This owes to the settling of the stars into virialised and stellar–dominatedconfigurations before the onset of feedback. By contrast, the effects of feedback on the observable properties of theclusters – their U–, B– and V–band magnitudes – are strong and sudden. The timescales on which the clusters becomevisible and unobscured are short compared with the timescales which the clouds are actually destroyed.

Accepted by MNRAS

http://arxiv.org/pdf/1504.05896

Dust trapping by spiral arms in gravitationally unstable protostellar discs

Giovanni Dipierro1, Paola Pinilla2, Giuseppe Lodato1, and Leonardo Testi3,4,5

1 Dipartimento di Fisica, Universit degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy2 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands3 European Southern Observatory, Karl Schwarzschild str. 2, D-85748 Garching bei Mnchen, Germany4 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy5 Excellence Cluster Universe, Boltzmann str. 2, D-85748 Garching bei Munchen, Germany

E-mail contact: giovanni.dipierro at unimi.it

In this paper we discuss the influence of gravitational instabilities in massive protostellar discs on the dynamics of dustgrains. Starting from a Smoothed Particle Hydrodynamics (SPH) simulation, we have computed the evolution of thedust in a quasi-static gas density structure typical of self-gravitating disc. For different grain size distributions we haveinvestigated the capability of spiral arms to trap particles. We have run 3D radiative transfer simulations in order toconstruct maps of the expected emission at (sub-)millimetre and near-infrared wavelengths. Finally, we have simulatedrealistic observations of our disc models at (sub-)millimetre and near-infrared wavelengths as they may appear with theAtacama Large Millimetre/sub-millimetre Array (ALMA) and the High-Contrast Coronographic Imager for AdaptiveOptics (HiCIAO) in order to investigate whether there are observational signatures of the spiral structure. We findthat the pressure inhomogeites induced by gravitational instabilities produce a non-negligible dynamical effect oncentimetre sized particles leading to significant overdensities in spiral arms. We also find that the spiral structureis readily detectable by ALMA over a wide range of (sub-)millimetre wavelengths and by HiCIAO in near-infraredscattered light for non-face-on discs located in the Ophiucus star-forming region. In addition, we find clear spatialspectral index variations across the disc, revealing that the dust trapping produces a migration of large grains thatcan be potentially investigated through multi-wavelenghts observations in the (sub-)millimetric. Therefore, the spiralarms observed to date in protoplanetary disc might be interpreted as density waves induced by the development ofgravitational instabilities.

Accepted by MNRAS

http://arxiv.org/pdf/1504.08099

The number fraction of discs around brown dwarfs in Orion OB1a and the 25 Orionisgroup

Juan Jose Downes1,2, Carlos Roman-Zuniga1, Javier Ballesteros-Paredes3, Cecilia Mateu1,2, Cesar Briceno4,Jesus Hernandez2, Monika G. Petr-Gotzens6, Nuria Calvet5, Lee Hartmann5 and Karina Mauco3

1 Instituto de Astronomıa, UNAM, Ensenada, C.P. 22860, Baja California, Mexico2 Centro de Investigaciones de Astronomıa, AP 264, Merida 5101-A, Venezuela3 Centro de Radioastronomıa y Astrofısica, UNAM. Apartado Postal 72-3 (Xangari), Morelia, Michoacan 58089,Mexico4 Cerro Tololo Interamerican Observatory, Casilla 603, La Serena, Chile5 Department of Astronomy, University of Michigan, 825 Dennison Building, 500 Church Street, Ann Arbor, MI 48109,

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USA6 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei Munchen, Germany

E-mail contact: jdownes at astrosen.unam.mx

We present a study of 15 new brown dwarfs belonging to the ∼ 7 Myr old 25 Orionis group and Orion OB1a sub-association with spectral types between M6 and M9 and estimated masses between ∼ 0.07 M⊙ and ∼ 0.01 M⊙. By

comparing them through a Bayesian method with low mass stars (0.8<∼M/M⊙<∼ 0.1) from previous works in the 25

Orionis group, we found statistically significant differences in the number fraction of classical T Tauri stars, weakT Tauri stars, class II, evolved discs and purely photospheric emitters at both sides of the sub-stellar mass limit.Particularly we found a fraction of 3.9+2.4

−1.6 % low mass stars classified as CTTS and class II or evolved discs, against

a fraction of 33.3+10.8−9.8 % in the sub-stellar mass domain. Our results support the suggested scenario in which the

dissipation of discs is less efficient for decreasing mass of the central object.

Accepted by Monthly Notices of the Royal Astronomical Society

http://arxiv.org/pdf/1504.05196

The difficult early stages of embedded star clusters and the importance of the pre-gasexpulsion virial ratio

J.P. Farias1, R. Smith1,2,3, M. Fellhauer1, S. Goodwin4, G.N. Candlish1, M. Blana1,5, R. Dominguez1

1 Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion, Chile2 Yonsei University, Graduate School of Earth System Sciences-Astronomy-Atmospheric Sciences, Yonsei-ro 50, Seoul120-749, Republic of Korea3 Laboratoire AIM Paris-Saclay, CEA/IRFU/SAp, CNRS/INSU, Universite Paris Diderot, 91191 Gif-sur-YvetteCedex, France4 Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH,UK5 Max-Planck-Institut fur extraterrestrische Physik, Gieenbachstraße 1, D-85748 Garching, Germany

E-mail contact: jfarias at asto-udec.cl

We examine the effects of gas-expulsion on initially substructured distributions of stars. We perform N-body sim-ulations of the evolution of these distributions in a static background potential to mimic the gas. We remove thestatic potential instantaneously to model gas-expulsion. We find that the exact dynamical state of the cluster playsa very strong role in affecting a cluster’s survival, especially at early times: they may be entirely destroyed or onlyweakly affected. We show that knowing both detailed dynamics and relative star-gas distributions can provide a goodestimate of the post-gas expulsion state of the cluster, but even knowing these is not an absolute way of determiningthe survival or otherwise of the cluster.

Accepted by MNRAS

http://arxiv.org/pdf/1504.02474

Inefficient star formation through turbulence, magnetic fields and feedback

Christoph Federrath1

1 Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611, Australia

E-mail contact: christoph.federrath at anu.edu.au

Star formation is inefficient. Only a few percent of the available gas in molecular clouds forms stars, leading to theobserved low star formation rate (SFR). The same holds when averaged over many molecular clouds, such that theSFR of whole galaxies is again surprisingly low. Indeed, considering the low temperatures, molecular clouds shouldbe highly gravitationally unstable and collapse on their global mean freefall timescale. And yet, they are observedto live about 10–100 times longer, i.e., the SFR per freefall time (SFRff) is only a few percent. Thus, other physicalmechanisms must counteract the quick global collapse. Turbulence, magnetic fields and stellar feedback have beenproposed as regulating agents, but it is still unclear which of these processes is the most important and what theirrelative contributions are. Here we run high-resolution simulations including gravity, turbulence, magnetic fields, and

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jet/outflow feedback. We confirm that clouds collapse on a mean freefall time, if only gravity is considered, producingstars at an unrealistic rate. In contrast, if turbulence, magnetic fields, and feedback are included step-by-step, theSFR is reduced by a factor of 2–3 with each additional physical ingredient. When they all act in concert, we find aconstant SFRff = 0.04, currently the closest match to observations, but still about a factor of 2–4 higher than theaverage. A detailed comparison with other simulations and with observations leads us to conclude that only modelswith turbulence producing large virial parameters, and including magnetic fields and feedback can produce realisticSFRs.

Accepted by MNRAS

http://astrobites.org/2015/04/28/why-is-star-formation-so-inefficient/

Resolving the chemical substructure of Orion-KL

S. Feng1, H. Beuther1, Th. Henning1, D. Semenov1, Aina Palau2 and E. A. C. Mills3

1 Max-Planck Institute for Astronomy, Heidelberg, Germany2 Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico3 National Radio Astronomy Observatory, USA

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

The Kleinmann-Low nebula in Orion (Orion-KL) is the nearest example of a high-mass star-forming environment.For the first time, we complemented 1.3 mm Submillimeter Array (SMA) interferometric line survey with IRAM 30m single-dish observations of the Orion-KL region. Covering a 4 GHz bandwidth in total, this survey contains over160 emission lines from 20 species (25 isotopologues), including 10 complex organic molecules (COMs).At a spatial resolution of ∼1200 AU, the continuum substructures are resolved. Extracting the spectra from individualsubstructures and providing the intensity-integrated distribution map for each species, we studied the small-scale chem-ical variations in this region. Our main results are: (1) We identify lines from the low-abundance COMs CH3COCH3

and CH3CH2OH, as well as tentatively detect CH3CHO and long carbon-chains C6H and HC7N. (2) We find thatwhile most COMs are segregated by type, peaking either towards the hot core (e.g., nitrogen-bearing species) or thecompact ridge (e.g., oxygen-bearing species like HCOOCH3, CH3OCH3, the distributions of others do not follow thissegregated structure (e.g., CH3CH2OH, CH3OH, CH3COCH3). (3) We find a second velocity component of HNCO,34SO2, and SO lines, which may be associated with a strong shock event in the low-velocity outflow. (4) Temperaturesand molecular abundances show large gradients between central condensations and the outflow regions, illustrating atransition between hot molecular core and shock-chemistry dominated regimes.Our observations of spatially resolved chemical variations in Orion-KL provide the nearest reference source for hotmolecular core and outflow chemistry, which will be an important example for interpreting the chemistry of moredistant HMSFRs.

Accepted by Astronomy & Astrophysics

http://arxiv.org/pdf/1504.08012

Tracing the magnetic field morphology of the Lupus I molecular cloud

G.A.P. Franco1 and F.O. Alves2

1 Departamento de Fısica – ICEx – UFMG, Belo Horizonte, Brazil2 Max-Planck-Institut fur extraterrestrische Physik, Garching, Germany

E-mail contact: franco at franco.ufmg.br

Deep R-band CCD linear polarimetry collected for fields with lines-of-sight toward the Lupus I molecular cloud isused to investigate the properties of the magnetic field within this molecular cloud. The observed sample containsabout 7000 stars, almost 2000 of them with polarization signal-to-noise ratio larger than 5. These data cover almostthe entire main molecular cloud and also sample two diffuse infrared patches in the neighborhood of Lupus I. Thelarge scale pattern of the plane-of-sky projection of the magnetic field is perpendicular to the main axis of Lupus I,but parallel to the two diffuse infrared patches. A detailed analysis of our polarization data combined with theHerschel/SPIRE 350µm dust emission map shows that the principal filament of Lupus I is constituted by three mainclumps acted by magnetic fields having different large-scale structure properties. These differences may be the reason

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for the observed distribution of pre- and protostellar objects along the molecular cloud and its apparent evolutivestage. On the other hand, assuming that the magnetic field is composed by a large-scale and a turbulent components,we find that the latter is rather similar in all three clumps. The estimated plane-of-sky component of the large-scalemagnetic field ranges from about 70µG to 200µG in these clumps. The intensity increases towards the Galactic plane.The mass-to-magnetic flux ratio is much smaller than unity, implying that Lupus I is magnetically supported on largescales.

Accepted by The Astrophysical Journal

http://arxiv.org/pdf/1504.08222

Prestellar Core Formation, Evolution, and Accretion from Gravitational Fragmentationin Turbulent Converging Flows

Munan Gong1 and Eve C. Ostriker1

1 Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544, USA

E-mail contact: munan at princeton.edu

We investigate prestellar core formation and accretion based on three-dimensional hydrodynamic simulations. Oursimulations represent local ∼1 pc regions within giant molecular clouds where a supersonic turbulent flow converges,triggering star formation in the post-shock layer. We include turbulence and self-gravity, applying sink particletechniques, and explore a range of inflow Mach number M = 2–16. Two sets of cores are identified and compared:t1-cores are identified of a time snapshot in each simulation, representing dense structures in a single cloud map;tcoll-cores are identified at their individual time of collapse, representing the initial mass reservoir for accretion. Wefind that cores and filaments form and evolve at the same time. At the stage of core collapse, there is a well-defined,converged characteristic mass for isothermal fragmentation that is comparable to the critical Bonner-Ebert mass atthe post-shock pressure. The core mass functions (CMFs) of tcoll-cores show a deficit of high-mass cores (>∼7 M⊙)compared to the observed stellar initial mass function (IMF). However, the CMFs of t1-cores are similar to the observedCMFs and include many low-mass cores that are gravitationally stable. The difference between t1-cores and tcoll-coressuggests that the full sample from observed CMFs may not evolve into protostars. Individual sink particles accrete ata roughly constant rate throughout the simulations, gaining one tcoll-core mass per free-fall time even after the initialmass reservoir is accreted. High-mass sinks gain proportionally more mass at late times than low-mass sinks. Thereare outbursts in accretion rates, resulting from clumpy density structures falling into the sinks.

Accepted by ApJ

http://arxiv.org/pdf/1504.02140

Early Results from VLT SPHERE: Long-Slit Spectroscopy of 2MASS 0122-2439B, aYoung Companion Near the Deuterium Burning Limit.

Sasha Hinkley1, Brendan P. Bowler2,8, Arthur Vigan3,4, Kimberly M. Aller5, Michael C. Liu5, Dim-itri Mawet6,4, Elisabeth Matthews1, Zahed Wahhaj4, Stefan Kraus1, Isabelle Baraffe1,7 and GillesChabrier1,7

1 University of Exeter, Astrophysics Group, Physics Building, Stocker Road, Exeter, EX4 4QL, UK.2 Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd, Pasadena,CA 91125, USA3 Aix Marseille Universite, CNRS, LAM (Laboratoire d‘Astrophysique de Marseille) UMR 7326, 13388 Marseille,France.4 European Southern Observatory, Alonso de Cordova 3107, Vitcura, Santiago, Chile5 University of Hawaii, Institute of Astronomy, 2860 Woodlawn Drive, Honolulu, HI 96822, USA6 Department of Astronomy, California Institute of Technology, Mail Code 249-17, 1200 E. California Blvd, Pasadena,CA 91125, USA7 CRAL, ENS-Lyon (CNRS UMR 5574), Lyon, France8 Caltech Joint Center for Planetary Astronomy Fellow.

E-mail contact: shinkley at gmail.com

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We present 0.95–1.80 µm spectroscopy of the ∼12–27 MJup companion orbiting the faint (R∼13.6), young (∼120Myr)M-dwarf 2MASS J01225093–2439505 (“2M0122–2439B”) at 1.5 arcsecond separation (50AU). Our coronagraphic long-slit spectroscopy was obtained with the new high contrast imaging platform VLT-SPHERE during Science Verification.The unique long-slit capability of SPHERE enables spectral resolution an order of magnitude higher than other extremeAO exoplanet imaging instruments. With a low mass, cool temperature, and very red colors, 2M0122–2439B occupiesa particularly important region of the substellar color-magnitude diagram by bridging the warm directly imaged hotplanets with late-M/early-L spectral types (e.g. β Pic b and ROXs 42Bb) and the cooler, dusty objects near the L/Ttransition (HR 8799bcde and 2MASS 1207b). We fit BT-Settl atmospheric models to our R≈350 spectrum and findTeff=1600±100 K and log(g)=4.5±0.5 dex. Visual analysis of our 2M0122–2439 B spectrum suggests a spectral typeL3-L4, and we resolve shallow J-band alkali lines, confirming its low gravity and youth. Specifically, we use the Allers& Liu (2013) spectral indices to quantitatively measure the strength of the FeH, VO, KI, spectral features, as well asthe overall H-band shape. Using these indices, along with the visual spectral type analysis, we classify 2M0122–2439B as an intermediate gravity (“INT-G”) object with spectral type L3.7±1.0.

Accepted by ApJ Letters

http://arxiv.org/pdf/1504.07240

Interplay of gas and ice during cloud evolution

S. Hocuk1,2 and S. Cazaux2

1 Max-Planck-Institut fur extraterrestrische Physik, Giessenbachstrasse 1, 85748, Garching, Germany2 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands

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

During the evolution of diffuse clouds to molecular clouds, gas-phase molecules freeze out on surfaces of small dustparticles to form ices. On dust surfaces, water is the main constituent of the icy mantle in which a complex chemistryis taking place. We aim to study the formation pathways and the composition of the ices throughout the evolutionof diffuse clouds. For this purpose, we used time-dependent rate equations to calculate the molecular abundances inthe gas phase and on solid surfaces (onto dust grains). We fully considered the gas-dust interplay by including thedetails of freeze-out, chemical and thermal desorption, and the most important photo-processes on grain surfaces. Thedifference in binding energies of chemical species on bare and icy surfaces was also incorporated into our equations.Using the numerical code flash, we performed a hydrodynamical simulation of a gravitationally bound diffuse cloudand followed its contraction. We find that while the dust grains are still bare, water formation is enhanced bygrain surface chemistry that is subsequently released into the gas phase, enriching the molecular medium. The COmolecules, on the other hand, tend to gradually freeze out on bare grains. This causes CO to be well mixed andstrongly present within the first ice layer. Once one monolayer of water ice has formed, the binding energy of the grainsurface changes significantly, and an immediate and strong depletion of gas-phase water and CO molecules occurs.While hydrogenation converts solid CO into formaldehyde (H2CO) and methanol (CH3OH), water ice becomes themain constituent of the icy grains. Inside molecular clumps formaldehyde is more abundant than water and methanolin the gas phase, owing its presence in part to chemical desorption.

Accepted by Astronomy & Astrophysics

http://adsabs.harvard.edu/abs/2015A\%26A...576A..49H

Long-term multicolor photometry of the young stellar objects FHO 26, FHO 27, FHO28, FHO 29 and V1929 Cygni

S.I. Ibryamov1, E.H. Semkov1 and S.P. Peneva1

1 Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72, TsarigradskoShose Blvd., 1784 Sofia, Bulgaria

E-mail contact: sibryamov at astro.bas.bg

Results from long-term multicolor optical photometric observations of the pre-main sequence stars FHO 26, FHO27, FHO 28, FHO 29 and V1929 Cyg collected during the period from June 1997 to December 2014 are presented.The objects are located in the dense molecular cloud L935, named ”Gulf of Mexico”, in the field between the North

23

America and Pelican nebulae. All stars from our study exhibit strong photometric variability in all optical passbands.Using our BVRI observations and data published by other authors, we tried to define the reasons for the observedbrightness variations. The presented paper is a part of our long-term photometric study of the young stellar objectsin the region of ”Gulf of Mexico”.

Accepted by Publications of the Astronomical Society of Australia (PASA)

http://arxiv.org/pdf/1504.06774

A debris disk under the influence of a wide planetary mass companion: The system ofHD106906

Lucie Jılkova1 and Simon Portegies Zwart1

1 Leiden Observatory, Niels Bohrweg 2, Leiden, 2333 CA, The Netherlands

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

The 13 Myr old star HD106906 is orbited by a debris disk of at least 0.067 MMoon with an inner and outer radiusof 20 AU and 120 AU, respectively, and by a planet at a distance of 650 AU. We use this curious combination of aclose low-mass disk and a wide planet to motivate our simulations of this system. We study the parameter space ofthe initial conditions to quantify the mass loss from the debris disk and its lifetime under the influence of the planet.We find that when the planet orbits closer to the star than about 50 AU and with low inclination relative to the disk(less than about 10 ◦), more disk material is perturbed outside than inside the region constrained by observations ontimescales shorter than 1 Myr. Considering the age of the system, such a short lifetime of the disk is incompatiblewith the timescale for planet–planet scattering which is one of the scenarios suggested to explain the wide separationof the planet. For some configurations when the planet’s orbit is inclined with respect to the disk, the latter will startto wobble. We argue that this wobbling is caused by a mechanism similar to the Kozai–Lidov oscillations. We alsoobserve various resonant structures (such as rings and spiral arms) induced in the disk by the planet.

Accepted by MNRAS

http://arxiv.org/pdf/1504.05702

Ice chemistry in starless molecular cores

J. Kalvans1

1 Engineering Research Institute “Ventspils International Radio Astronomy Center” of Ventspils University College,Inzenieru 101, Ventspils, Latvia, LV-3601

E-mail contact: juris.kalvans at venta.lv

Starless molecular cores are natural laboratories for interstellar molecular chemistry research. The chemistry of icesin such objects was investigated with a three-phase (gas, surface, and mantle) model. We considered the center partof five starless cores, with their physical conditions derived from observations. The ice chemistry of oxygen, nitrogen,sulfur, and complex organic molecules (COMs) was analyzed. We found that an ice-depth dimension, measured, e.g.,in monolayers, is essential for modeling of chemistry in interstellar ices. Particularly, the H2O:CO:CO2:N2:NH3 iceabundance ratio regulates the production and destruction of minor species. It is suggested that photodesorption duringcore collapse period is responsible for high abundance of interstellar H2O2 and O2H, and other species synthesizedon the surface. The calculated abundances of COMs in ice were compared to observed gas-phase values. Smalleractivation barriers for CO and H2CO hydrogenation may help explain the production of a number of COMs. Theobserved abundance of methyl formate HCOOCH3 could be reproduced with a 1kyr, 20K temperature spike. Possibledesorption mechanisms, relevant for COMs, are gas turbulence (ice exposure to interstellar photons) or a weak shockwithin the cloud core (grain collisions). To reproduce the observed COM abundances with the present 0D model,1–10% of ice mass needs to be sublimated. We estimate that the lifetime for starless cores likely does not exceed1Myr. Taurus cores are likely to be younger than their counterparts in most other clouds.

Accepted by ApJ

http://arxiv.org/pdf/1504.06065

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A Ring of C2H in the Molecular Disk Orbiting TW Hya

Joel H. Kastner1, Chunhua Qi2, Uma Gorti3, Pierre Hily-Blant4,5, Karin Oberg2, Thierry Forveille4,Sean Andrews2, David Wilner2

1 Chester F. Carlson Center for Imaging Science, School of Physics & Astronomy, and Laboratory for MultiwavelengthAstrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester NY 14623 USA2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 021383 SETI Institute, 189 Bernardo Ave., Mountain View, CA 94043, USA; NASA Ames Research Center, Moffett Field,CA 94035, USA4 Universite Grenoble Alpes, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG), F-38000, Grenoble,France; CNRS, IPAG, F-38000, Grenoble, France5 Institut Universitaire de France, F-38000, Grenoble, France

E-mail contact: jhk at cis.rit.edu

We have used the Submillimeter Array to image, at ∼1.′′5 resolution, C2H (3–2) emission from the circumstellar diskorbiting the nearby (D = 54 pc), ∼8 Myr-old, ∼0.8 M⊙ classical T Tauri star TW Hya. The SMA imaging revealsthat the C2H emission exhibits a ring-like morphology. Based on a model in which the C2H column density followsa truncated radial power-law distribution, we find that the inner edge of the ring lies at ∼45 AU, and that the ringextends to at least ∼120 AU. Comparison with previous (single-dish) observations of C2H (4–3) emission indicatesthat the C2H molecules are subthermally excited and, hence, that the emission arises from the relatively warm,tenuous upper atmosphere of the disk. We propose that the C2H emission most likely traces particularly efficientphoto-destruction of small grains and/or photodesorption and photodissociation of hydrocarbons derived from grainice mantles in the surface layers of the outer disk. The presence of a C2H ring in the TW Hya disk hence likely servesas a marker of dust grain processing and radial and vertical grain size segregation within the disk.

Accepted by ApJ

http://arxiv.org/pdf/1504.05980

Formation of Super-Earth Mass Planets at 125–250 AU from a Solar-type Star

Scott J. Kenyon1 and Benjamin C. Bromley2

1 Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 USA2 Department of Physics, University of Utah, 201 JFB, Salt Lake City, UT 84112 USA

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

We investigate pathways for the formation of icy super-Earth mass planets orbiting at 125–250 AU around a 1 M⊙

star. An extensive suite of coagulation calculations demonstrates that swarms of 1 cm to 10 m planetesimals can formsuper-Earth mass planets on time scales of 1–3 Gyr. Collisional damping of 10−2 − 102 cm particles during oligarchicgrowth is a highlight of these simulations. In some situations, damping initiates a second runaway growth phasewhere 1000–3000 km protoplanets grow to super-Earth sizes. Our results establish the initial conditions and physicalprocesses required for in situ formation of super-Earth planets at large distances from the host star. For nearby dustydisks in HD 107146, HD 202628, and HD 207129, ongoing super-Earth formation at 80–150 AU could produce gapsand other structures in the debris. In the solar system, forming a putative planet X at a < 300 AU (a > 1000 AU)requires a modest (very massive) protosolar nebula.

Accepted by Astrophysical Journal

http://arxiv.org/pdf/1501.05659

Evidence for Decay of Turbulence by MHD Shocks in Molecular Clouds via CO Emission

Rebecca L. Larson1, Neal J. Evans II1, Joel D. Green1,2 and Yao-Lun Yang1

1 University of Texas at Austin, Department of Astronomy, Austin, TX2 Space Telescope Science Institute, Baltimore, MD

E-mail contact: saturnswings at gmail.com

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We utilize observations of sub-millimeter rotational transitions of CO from a Herschel Cycle 2 open time program(“COPS”, PI: J. Green) to identify previously predicted turbulent dissipation by magnetohydrodynamic (MHD) shocksin molecular clouds. We find evidence of the shocks expected for dissipation of MHD turbulence in material notassociated with any protostar. Two models fit about equally well: model 1 has a density of 103 cm−3, a shock velocityof 3 km s−1, and a magnetic field strength of 4 µG; model 2 has a density of 103.5 cm−3, a shock velocity of 2 km s−1,and a magnetic field strength of 8 µG. Timescales for decay of turbulence in this region are comparable to crossingtimes. Transitions of CO up to J of 8, observed close to active sites of star formation, but not within outflows,can trace turbulent dissipation of shocks stirred by formation processes. Although the transitions are difficult todetect at individual positions, our Herschel-SPIRE survey of protostars provides a grid of spatially-distributed spectrawithin molecular clouds. We averaged all spatial positions away from known outflows near seven protostars. We findsignificant agreement with predictions of models of turbulent dissipation in slightly denser (103.5 cm−3) material witha stronger magnetic field (24 µG) than in the general molecular cloud.

Accepted by The Astrophysical Journal

http://arxiv.org/pdf/1505.00847

Smoothed particle magnetohydrodynamic simulations of protostellar outflows with mis-aligned magnetic field and rotation axes

Benjamin T. Lewis1,2, Matthew R. Bate1,2 and Daniel J. Price2

1 School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK2 Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Clayton, Vic 3800, Australia

E-mail contact: blewis at astro.ex.ac.uk

We have developed a modified form of the equations of smoothed particle magnetohydrodynamics which are sta-ble in the presence of very steep density gradients. Using this formalism, we have performed simulations of thecollapse of magnetised molecular cloud cores to form protostars and drive outflows. Our stable formalism allowsfor smaller sink particles (< 5 AU) than used previously and the investigation of the effect of varying the an-gle, θ, between the initial field axis and the rotation axis. The nature of the outflows depends strongly on thisangle: jet-like outflows are not produced at all when θ > 30◦, and a collimated outflow is not sustained whenθ > 10◦. No substantial outflows of any kind are produced when θ > 60◦. This may place constraints on thegeometry of the magnetic field in molecular clouds where bipolar outflows are seen. Animations can be found athttp://www.astro.ex.ac.uk/people/blewis/research/outflows misaligned fields.html

Accepted by MNRAS

http://arxiv.org/pdf/1504.08322v1

G-virial: Gravity-based structure analysis of molecular clouds

Guang-Xing Li1, Friedrich Wyrowski1, Karl Menten1, Tom Megeath2 and Xun Shi3

1 MPIfR Bonn, Germany2 University of Toledo, USA3 MPA Garching, Germany

E-mail contact: gxli at mpifr.de

Accepted by A&A

We present the G-virial method (http://gxli.github.io/G-virial/) which aims to quantify (1) the importance of gravityin molecular clouds in the position-position-velocity (PPV) space, and (2) properties of the gas condensations inmolecular clouds. Different from previous approaches that calculate the virial parameter for different regions, ournew method takes gravitational interactions between all the voxels in 3D PPV data cubes into account, and generatesmaps of the importance of gravity. This map can be combined with the original data cube to derive relations such asthe mass-radius relation. Our method is important for several reasons. First, it offers the the ability to quantify thecentrally condensed structures in the 3D PPV data cubes, and enables us to compare them in an uniform framework.Second, it allows us to understand the importance of gravity at different locations in the data cube, and provides a

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global picture of gravity in clouds. Third, it offers a robust approach to decomposing the data into different regionswhich are gravitationally coherent. To demonstrate the application of our method we identified regions from thePerseus and Ophiuchus molecular clouds, and analyzed their properties. We found an increase in the importance ofgravity towards the centers of the individual molecular condensations. We also quantified the properties of the regionsin terms of mass-radius and mass-velocity relations. Through evaluating the virial parameters based on the G-virial,we found that all our regions are almost gravitationally bound. Cluster-forming regions appear are more centrallycondensed.

Accepted by A&A

http://arxiv.org/pdf/1504.01003

ALMA Resolves the Spiraling Accretion Flow in the Luminous OB Cluster-FormingRegion G33.92+0.11

Hauyu Baobab Liu1, Roberto Galvan-Madrid2, Izaskun Jimenez-Serra3, Carlos Roman-Zuniga4, QizhouZhang5, Zhiyun Li6 and Huei-Ru Chen7

1 Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan2 Centro de Radioastronomia y Astrofisica, UNAM, A.P. 3-72, Xangari, Morelia 58089, Mexico3 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany4 Instituto de Astronomia, UNAM, Unidad Academica en Ensenada, Ensenada 22860, Mexico5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA6 Department of Astronomy, P.O. Box 400325, Charlottesville, VA 22904, USA7 Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

E-mail contact: baobabyoo at gmail.com

How rapidly collapsing parsec-scale massive molecular clumps feed high-mass stars, and how they fragment to form OBclusters, have been outstanding questions in the field of star-formation. In this work, we report the resolved structuresand kinematics of the approximately face-on, rotating massive molecular clump, G33.92+0.11. Our high resolutionAtacama Large Millimeter/submillimeter Array (ALMA) images show that the spiral arm-like gas overdensities formin the eccentric gas accretion streams. First, we resolved that the dominant part of the ∼0.6 pc scale massive molecularclump (3.0+2.8

−1.4·103 M⊙) G33.92+0.11A is tangled with several 0.5-1 pc size molecular arms spiraling around it, which

may be connected further to exterior gas accretion streams. Within G33.92+0.11A, we resolved the ∼0.1 pc width gasmini-arms connecting with the two central massive (100-300 M⊙) molecular cores. The kinematics of arms and coreselucidate a coherent accretion flow continuing from large to small scales. We demonstrate that the large moleculararms are indeed the cradles of dense cores, which are likely current or future sites of high-mass star formation. Sincethese deeply embedded massive molecular clumps preferentially form the highest mass stars in the clusters, we arguethat dense cores fed by or formed within molecular arms play a key role in making the upper end of the stellar andcore mass functions.

Accepted by ApJ (804, 37, 2015)

Far-infrared CO and H2O emission in intermediate-mass protostars

M. Matuszak1, A. Karska1, L. E. Kristensen2, G. J. Herczeg3, L. Tychoniec1,T.A. van Kempen4 and A. Fuente5

1 Astronomical Observatory, Adam Mickiewicz University, Sloneczna 36, PL-60-268 Poznan, Poland2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA3 Kavli Institut for Astronomy and Astrophysics, Yi He Yuan Lu 5, HaiDian Qu, Peking University, Beijing, 100871,PR China4 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands4 Observatorio Astronomico Nacional (OAN, IGN), Apdo 112, 28803 Alcala de Henares, Spain

E-mail contact: agata.karska at amu.edu.pl

Context: Intermediate-mass young stellar objects (YSOs) provide a link to understanding how feedback from shocksand UV radiation scales from low- to high-mass star forming regions.

27

Aims: Our aim is to analyze excitation of CO and H2O in deeply embedded intermediate-mass YSOs and compareit with similar studies on low-mass and high-mass YSOs.Methods: Herschel/PACS spectral maps are analyzed for six YSOs with bolometric luminosities of Lbol ∼ 102 − 103

L⊙. The maps cover spatial scales of ∼ 104 AU in several CO and H2O lines located in the ∼ 55− 210 µm range.Results: Rotational diagrams of CO show two temperature components at Trot ∼ 320 K and Trot ∼ 700 − 800 K,comparable to low- and high-mass protostars probed at similar spatial scales. The diagrams for H2O show a singlecomponent at Trot ∼ 130 K, as seen in low-mass protostars, and about 100 K lower than in high-mass protostars. Sincethe uncertainties in Trot are on the same order as the difference between the intermediate and high-mass protostars, wecannot conclude whether the change in rotational temperature occurs at a specific luminosity or whether the changeis more gradual from low- to high-mass YSOs.Conclusions: Molecular excitation in intermediate-mass protostars is comparable to the central 103 AU of low-massprotostars and consistent within the uncertainties with the high-mass protostars probed at 3 ·103 AU scales, suggestingsimilar shock conditions in all those sources.

Accepted by A&A

http://arxiv.org/pdf/1504.03347

The Pillars of Creation revisited with MUSE: gas kinematics and high-mass stellarfeedback traced by optical spectroscopy

A.F. Mc Leod1, J.E. Dale2,3, A. Ginsburg1, B. Ercolano2,3, M. Gritschneder2, S. Ramsay1, and L.Testi1,4

1 European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei Mnchen, Germany2 Universitats-Sternwarte Munchen, Scheinerstr. 1, D-81679 Mnchen, Germany3 Excellence Cluster ‘Universe’, Boltzmannstr. 2, D-85748 Garching bei Munchen, Germany4 INAF/Osservatorio Astrofisico of Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy

E-mail contact: amcleod at eso.org

Integral field unit (IFU) data of the iconic Pillars of Creation in M16 are presented. The ionisation structure of thepillars was studied in great detail over almost the entire visible wavelength range, and maps of the relevant physicalparameters, e.g. extinction, electron density, electron temperature, line-of-sight velocity of the ionised and neutral gasare shown. In agreement with previous authors, we find that the pillar tips are being ionised and photo-evaporatedby the massive members of the nearby cluster NGC 6611. They display a stratified ionisation structure where theemission lines peak in a descending order according to their ionisation energies. The IFU data allowed us to analyse thekinematics of the photo-evaporative flow in terms of the stratified ionisation structure, and we find that, in agreementwith simulations, the photo-evaporative flow is traced by a blueshift in the position-velocity profile. The gas kinematicsand ionisation structure have allowed us to produce a sketch of the 3D geometry of the Pillars, positioning the pillarswith respect to the ionising cluster stars. We use a novel method to detect a previously unknown bipolar outflowat the tip of the middle pillar and suggest that it has an embedded protostar as its driving source. Furthermore weidentify a candidate outflow in the leftmost pillar. With the derived physical parameters and ionic abundances, weestimate a mass loss rate due to the photo-evaporative flow of 70 M⊙ Myr−1 which yields an expected lifetime ofapproximately 3 Myr.

Accepted by MNRAS

http://arxiv.org/pdf/1504.03323

Detailed Kinematic Investigation of Herbig-Haro Objects in the Northeast Region ofNGC 7129

T.A. Movsessian1, T.Yu. Magakian1, A.V. Moiseev2 and M.G. Gevorgian1

1 Byurakan Astrophysical Observatory, Byurakan, 0213 Armenia2 Special Astrophysical Observatory, RAS, Nizhnii Arkhyz, 369167 Russia

E-mail contact: tigmov at web.am

Using the Fabry-Perot scanning interferometer at the SAO RAS 6-m telescope, we studied a number of Herbig-Haro

28

objects in the northeast region of NGC 7129. We detected a helicoidal flow in HH 234, consisting of separate high-speed knots propagating within the cavity in interstellar medium created by the outflow. HH 235 consists of at leastfive knots, each of which form its own bow shock. The direction of these fronts together with the NW-SE orientedhigh-velocity core of the flow indicates the location of a possible source. The origin of the objects HH 105 and HH 821is discussed as well. Possible Herbig-Haro outflow sources in this region are located further north of the cluster centerin the vicinity of the active star V350 Cep, except for HH 234 with a known source. It can be considered ascertainedthat NGC 7129 region consists of several star-forming cores, in which the multiple outflows from stars of differentmasses are present.

Accepted by Astrophysical Bulletin (Vol. 70, No. 2, 2015)

C2H observations toward the Orion Bar

Z. Nagy1,2, V. Ossenkopf2, F. F. S. van der Tak3, A. Faure4, Z. Makai2 and E. A. Bergin5

1 Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA2 I. Physikalisches Institut, Universitat zu Koln, Zulpicher Str. 77, 50937 Koln, Germany3 Kapteyn Astronomical Institute, University of Groningen and SRON Netherlands Institute for Space Research,Landleven 12, 9747 AD Groningen, The Netherlands4 Universite Joseph Fourier/CNRS, Institut de Planetologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041Grenoble, France5 University of Michigan, Ann Arbor, MI 48197, USA

E-mail contact: zsofia.nagy.astro at gmail.com

The ethynyl radical (C2H) is one of the first radicals to be detected in the interstellar medium. Its higher rotationaltransitions have recently become available with the Herschel Space Observatory.We aim to constrain the physical parameters of the C2H emitting gas toward the Orion Bar.We analyse the C2H line intensities measured toward the Orion Bar CO+ Peak and Herschel/HIFI maps of C2H,CH, and HCO+, and a NANTEN map of [Ci]. We interpret the observed C2H emission using the combination ofHerschel/HIFI and NANTEN data with radiative transfer and PDR models.Five rotational transitions of C2H (from N=6−5 up to N=10−9) have been detected in the HIFI frequency rangetoward the CO+ peak of the Orion Bar. Based on the five detected C2H transitions, a single component rotationaldiagram analysis gives a rotation temperature of ∼64 K and a beam-averaged C2H column density of 4× 1013 cm−2.The rotational diagram is also consistent with a two-component fit resulting in rotation temperatures of 43±0.2 K and123±21 K, and beam-averaged column densities of ∼ 8.3 × 1013 cm−2 and ∼ 2.3 × 1013 cm−2 for the three lower-Nand for the three higher-N transitions, respectively.The measured five rotational transitions cannot be explained by any single parameter model. According to a non-LTEmodel, most of the C2H column density produces the lower−N C2H transitions and traces a warm (Tkin ∼ 100− 150K) and dense (n(H2)∼105-106 cm−3) gas. A small fraction of the C2H column density is required to reproduce theintensity of the highest-N transitions (N=9−8 and N=10−9) originating from a high density (n(H2)∼5×106 cm−3)hot (Tkin ∼ 400 K) gas. The total beam-averaged C2H column density in the model is 1014 cm−2. A comparison ofthe spatial distribution of C2H to those of CH, HCO+, and [Ci] shows the best correlation with CH.Both the non-LTE radiative transfer model and a simple PDR model representing the Orion Bar with a plane-parallelslab of gas and dust suggest, that C2H cannot be described by a single pressure component, unlike the reactiveion CH+, which was previously analysed toward the Orion Bar CO+ peak. The physical parameters traced by thehigher rotational transitions (N=6-5,...,10-9) of C2H may be consistent with the edges of dense clumps exposed toUV radiation near the ionization front of the Orion Bar.

Accepted by A&A

http://arxiv.org/pdf/1405.3903

Demographics of transition discs in Ophiuchus and Taurus

Joan R. Najita1,2, Sean M. Andrews2 and James Muzerolle3

1 National Optical Astronomy Observatory, 950 N. Cherry Ave, Tucson, AZ 857192 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138

29

3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218

E-mail contact: najita at noao.edu

Transition disc systems are young stars that appear to be on the verge of dispersing their protoplanetary discs. Weexplore the nature of these systems by comparing the stellar accretion rates and disc masses of transition discs andnormal T Tauri stars in Taurus and Ophiuchus. After controlling for the known dependences of stellar accretion rateand disc mass on age, accretion rate on stellar mass, and disc mass on the presence of stellar or substellar companions,we find that the normal T Tauri stars show a trend of stellar accretion rate increasing with disc mass. The transitiondiscs tend to have higher average disc masses than normal T Tauri stars as well as lower accretion rates than normalT Tauri stars of the same disc mass. These results are most consistent with the interpretation that the transitiondiscs have formed objects massive enough to alter the accretion flow, i.e. single or multiple giant planets. SeveralOphiuchus T Tauri stars that are not known transition disc ???systems also have very low accretion rates for theirdisc masses. We speculate on the possible nature of these sources.

Accepted by MNRAS

http://arxiv.org/pdf/1504.05198

A Survey of Extended H2 Emission from Massive YSOs

Felipe Navarete1, Augusto Damineli1, Cassio L. Barbosa2 and Robert D. Blum3

1 Instituto de Astronomia, Geofisica e Ciencias Atmosfericas - University of Sao Paulo (IAG-USP)2 MCTI/Laboratorio Nacional de Astrofisica3 National Optical Astronomy Observatory (NOAO)

E-mail contact: navarete at usp.br

We present the results from a survey, designed to investigate the accretion process of massive young stellar objects(MYSOs) through near infrared narrow band imaging using the H2 ν=1-0 S(1) transition filter. A sample of 353Massive Young Stellar Object (MYSO) candidates was selected from the Red MSX Source survey using photometriccriteria at longer wavelengths (infrared and submillimeter) and chosen with positions throughout the Galactic Plane.Our survey was carried out at the SOAR Telescope in Chile and CFHT in Hawaii covering both hemispheres. The datareveal that extended H2 emission is a good tracer of outflow activity, which is a signpost of accretion process on youngmassive stars. Almost half of the sample exhibit extended H2 emission and 74 sources (21%) have polar morphology,suggesting collimated outflows. The polar-like structures are more likely to appear on radio-quiet sources, indicatingthese structures occur during the pre-UCHII phase. We also found an important fraction of sources associated withfluorescent H2 diffuse emission that could be due to a more evolved phase. The images also indicate only ∼23% (80)of the sample is associated with extant (young) stellar clusters. These results support the scenario in which massivestars are formed by accretion disks, since the merging of low mass stars would not produce outflow structures.

Accepted by MNRAS

http://arxiv.org/pdf/1504.06174

The Three-mm Ultimate Mopra Milky Way Survey. II. Cloud and Star Formation Nearthe Filamentary Ministarburst RCW 106

Hans Nguy˜en1,2, Quang Nguy˜en Lu’o’ng1,3,4, Peter G. Martin1, Peter J. Barnes5,6, Erik Muller4, VickiLowe7,8, Nadia Lo9, Maria Cunningham8, Frederique Motte10, Balthasar Indermuhle7, Stefan N. O’Dougherty11,Audra K. Hernandez12 and Gary A. Fuller13

1 Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S3H8, Canada2 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany3 EACOA Fellow at NAOJ, Japan & KASI, Korea4 National Astronomical Observatory of Japan, Chile Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan5 Astronomy Department, University of Florida, P.O. Box 112055, Gainesville, FL 32611, USA6 School of Science and Technology, University of New England, NSW 2351, Australia7 CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710, Australia

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8 School of Physics, University of New West Wales, NSW 2052 Australia9 Departamento de Astronomıa, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Casilla36-D, Chile10 Laboratoire AIM Paris-Saclay, CEA/IRFU - CNRS/INSU - Universite Paris Diderot, Service d’Astrophysique, Bat.709, CEA-Saclay, F-91191, Gif-sur-Yvette Cedex, France11 College of Optical Sciences, University of Arizona, 1630 E. University Blvd., P.O. Box 210094, Tucson, AZ 85721,USA12 Astronomy Department, University of Wisconsin, 475 East Charter St., Madison, WI 53706, USA13 Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, University ofManchester, Manchester, M13 3PL., UK

E-mail contact: hnguyen at mpifr-bonn.mpg.de

We report here a study of gas, dust and star formation rates (SFRs) in the molecular cloud complexes (MCCs)surrounding the giant H II region RCW106 using 12CO and 13CO (1-0) data from the Three-mm Ultimate MopraMilky way Survey (ThrUMMS) and archival data. We separate the emission in the Galactic Plane around l = 330◦-335◦ and b = −1◦-1◦ into two main MCCs: the RCW106 (VLSR = −48 km s−1) complex and the MCC331-90(VLSR =−90 km s−1) complex. While RCW106 (M∼ 5.9 × 106M⊙) is located in the Scutum-Centaurus arm at a distanceof 3.6 kpc, MCC331-90 (M∼ 2.8 × 106M⊙) is in the Norma arm at a distance of 5 kpc. Their molecular gas masssurface densities are ∼ 220 and ∼ 130M⊙ pc−2, respectively. For RCW106 complex, using the 21 cm continuum fluxesand dense clump counting, we obtain an immediate past (∼-0.2Myr) and an immediate future (∼+0.2Myr) SFRs of0.25+0.09

−0.023M⊙, yr−1 and 0.12± 0.1M⊙ yr−1. This results in an immediate past SFR density of 9.5+3.4

−0.9M⊙ yr−1 kpc−2

and an immediate future SFR density of 4.8+3.8−3.8M⊙ yr−1 kpc−2. As both SFRs in this cloud are higher than the

ministarburst threshold, they must be undergoing a ministarburst event although burst peak has already passed. Weconclude that this is one of the most active star forming complexes in the southern sky, ideal for further investigationsof massive star formation and potentially shedding light on the physics of high-redshift starbursts.

Accepted by ApJ

https://publications.mpifr-bonn.mpg.de/manuscripts/uploads/hnguyen1428574191.pdf

http://arxiv.org/pdf/1504.02246

Long-Slit Spectroscopy of Parsec-Scale Jets from DG Tauri

Heeyoung Oh1,2, Tae-Soo Pyo3,4, In-Soo Yuk2 and Byeong-Gon Park1,2

1 Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 305-350, Korea2 Korea Astronomy and Space Science Institute,776 Daedeokdae-ro, Yuseong-gu, Daejeon 305-348, Korea3 Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 967204 School of Mathematical and Physical Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama,Kanagawa 240-0193, Japan

E-mail contact: hyoh at kasi.re.kr

We present observational results from optical long-slit spectroscopy of parsec-scale jets of DG Tau. From HH 158 andHH 702, the optical emission lines of Hα, [O I] λλ6300, 6363, [N II] λλ6548, 6584, and [S II] λλ6716, 6731 are obtained.The kinematics and physical properties (i.e., electron density, electron temperature, ionization fraction, and mass-lossrate) are investigated along the blueshifted jet up to 650′′ distance from the source. For HH 158, the radial velocityranges from −50 to −250 km s−1. The proper motion of the knots is 0.′′196 − 0.′′272 yr−1. The electron density is ∼104

cm−3 close to the star, and decreases to ∼102 cm−3 at 14 arcsec away from the star. Ionization fraction indicatesthat the gas is almost neutral in the vicinity of the source. It increases up to over 0.4 along the distance. HH 702 islocated at 650 arcsec from the source. It shows ∼ −80 km s−1 in the radial velocity. Its line ratios are similar tothose at knot C of HH 158. The mass-loss rate is estimated to be about ∼ 10−7 M⊙ yr−1, which is similar to valuesobtained from previous studies.

Accepted by Journal of The Korean Astronomical Society

http://arxiv.org/pdf/1505.00942.pdf

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Circumstellar Disks revealed by H/K Flux Variation Gradients

F. Pozo Nunez1, M. Haas1, R. Chini1,2, M. Ramolla1, C. Westhues1 and K.-W. Hodapp3

1 Astronomisches Institut, Ruhr-Universitat Bochum, Universitatsstrasse 150, 44801 Bochum, Germany2 Instituto de Astronomia, Universidad Catolica del Norte, Avenida Angamos 0610, Casilla 1280 Antofagasta, Chile3 Institute for Astronomy, University of Hawaii, 640 N. Aohoku Place, Hilo HI 96720, USA

E-mail contact: fpozo at astro.rub.de

The variability of young stellar objects (YSO) changes their brightness and color preventing a proper classification intraditional color-color and color magnitude diagrams. We have explored the feasibility of the flux variation gradient(FVG) method for YSOs, using H and K band monitoring data of the star forming region RCW38 obtained atthe University Observatory Bochum in Chile. Simultaneous multi-epoch flux measurements follow a linear relationFH = α+β ·FK for almost all YSOs with large variability amplitude. The slope β gives the meanHK color temperatureTvar of the varying component. Because Tvar is hotter than the dust sublimation temperature, we have tentativelyassigned it to stellar variations. If the gradient does not meet the origin of the flux-flux diagram, an additional non- orless-varying component may be required. If the variability amplitude is larger at the shorter wavelength, e.g. α < 0,this component is cooler than the star (e.g. a circumstellar disk); vice versa, if α > 0, the component is hotter like ascattering halo or even a companion star. We here present examples of two YSOs, where the HK FVG implies thepresence of a circumstellar disk; this finding is consistent with additional data at J and L. One YSO shows a clearK-band excess in the JHK color-color diagram, while the significance of a K-excess in the other YSO depends onthe measurement epoch. Disentangling the contributions of star and disk it turns out that the two YSOs have hugevariability amplitudes (∼ 3− 5mag). The HK FVG analysis is a powerful complementary tool to analyze the varyingcomponents of YSOs and worth further exploration of monitoring data at other wavelengths.

Accepted by Astronomy and Astrophysics

http://arxiv.org/pdf/1504.07562

High-contrast imaging constraints on gas giant planet formation - The Herbig Ae/Bestar opportunity

Sascha P. Quanz1

1 ETH Zurich, Institute for Astronomy, Wolfgang-Pauli-Strasse, 8053 Zurich, Switzerland

E-mail contact: sascha.quanz at astro.phys.ethz.ch

Planet formation studies are often focused on solar-type stars, implicitly considering our Sun as reference point.This approach overlooks, however, that Herbig Ae/Be stars are in some sense much better targets to study planetformation processes empirically, with their disks generally being larger, brighter and simply easier to observe acrossa large wavelength range. In addition, massive gas giant planets have been found on wide orbits around early typestars, triggering the question if these objects did indeed form there and, if so, by what process. In the following Ibriefly review what we currently know about the occurrence rate of planets around intermediate mass stars, beforediscussing recent results from Herbig Ae/Be stars in the context of planet formation. The main emphasis is put onspatially resolved polarized light images of potentially planet forming disks and how these images - in combination withother data - can be used to empirically constrain (parts of) the planet formation process. Of particular interest aretwo objects, HD100546 and HD169142, where, in addition to intriguing morphological structures in the disks, directobservational evidence for (very) young planets has been reported. I conclude with an outlook, what further progresswe can expect in the very near future with the next generation of high-contrast imagers at 8-m class telescopes andtheir synergies with ALMA.

Accepted by Astrophysics and Space Science as invited short review in special issue about Herbig Ae/Be stars

http://arxiv.org/pdf/1504.04880

Confirmation and characterization of the protoplanet HD100546 b - Direct evidence forgas giant planet formation at 50 au

Sascha P. Quanz1, Adam Amara1, Michael R. Meyer1, Julien H. Girard2, Matthew A. Kenworthy3 and

32

Markus Kasper4

1 ETH Zurich, Institute for Astronomy, Wolfgang-Pauli-Strasse, 8053 Zurich, Switzerland2 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Cassilla 19001, Santiago, Chile3 Sterrewacht Leiden, P.O. Box 9513, Niels Bohrweg 2, 2300 RA Leiden, The Netherlands4 European Southern Observatory, Karl Schwarzschild Strasse, 2, 85748 Garching bei Munchen, Germany

E-mail contact: sascha.quanz at astro.phys.ethz.ch

We present the first multi-wavelength, high-contrast imaging study confirming the protoplanet embedded in the diskaround the Herbig Ae/Be star HD100546. The object is detected at L′ (∼ 3.8µm) and M ′ (∼ 4.8µm), but not atKs (∼ 2.1µm), and the emission consists of a point source component surrounded by spatially resolved emission.For the point source component we derive apparent magnitudes of L′ = 13.92 ± 0.10 mag, M ′ = 13.33 ± 0.16 mag,and Ks > 15.43 ± 0.11 mag (3σ limit), and a separation and position angle of (0.457 ± 0.014)′′ and (8.4 ± 1.4)◦,and (0.472± 0.014)′′ and (9.2 ± 1.4)◦ in L′ and M ′, respectively. We demonstrate that the object is co-moving withHD100546 and can reject any (sub-)stellar fore-/background object. Fitting a single temperature blackbody to theobserved fluxes of the point source component yields an effective temperature of Teff = 932+193

−202 K and a radius

for the emitting area of R = 6.9+2.7−2.9 RJupiter. The best-fit luminosity is L = (2.3+0.6

−0.4) · 10−4L⊙. We quantitatively

compare our findings with predictions from evolutionary and atmospheric models for young, gas giant planets, discussthe possible existence of a warm, circumplanetary disk, and note that the de-projected physical separation from thehost star of (53 ± 2) au poses a challenge standard planet formation theories. Considering the suspected existenceof an additional planet orbiting at ∼13–14 au, HD100546 appears to be an unprecedented laboratory to study theformation of multiple gas giant planets empirically.

Accepted by ApJ

http://arxiv.org/pdf/1412.5173

Sensitive survey for 13CO, CN, H2CO, and SO in the disks of T Tauri and Herbig Aestars II: Stars in ρ Oph and Upper Scorpius

L. Reboussin1,2, S. Guilloteau1,2, M. Simon3, N. Grosso4, V. Wakelam1,2, E. Di Folco1,2, A. Dutrey1,2

and V. Pietu5

1 Universite de Bordeaux, LAB, UMR 5804, F-33270, Floirac, France2 CNRS, LAB, UMR 5804, F-33270, Floirac, France3 Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA4 Observatoire Astronomique de Strasbourg, Universite de Strasbourg, CNRS, UMR 7550, 11 rue de l’Universite, 6700Strasbourg, France5 IRAM, 300 rue de la piscine, F-38406, Saint Martin d’Heres, France

E-mail contact: laura.reboussin at obs.u-bordeaux1.fr

We attempt to determine the molecular composition of disks around young low-mass stars in the ρ Oph region and tocompare our results with a similar study performed in the Taurus-Auriga region. We used the IRAM 30 m telescopeto perform a sensitive search for CN N=2-1 in 29 T Tauri stars located in the ρ Oph and upper Scorpius regions. 13COJ=2-1 is observed simultaneously to provide an indication of the level of confusion with the surrounding molecularcloud. The bandpass also contains two transitions of ortho-H2CO, one of SO, and the C17O J=2-1 line, which providescomplementary information on the nature of the emission. Contamination by molecular cloud in 13CO and even C17Ois ubiquitous. The CN detection rate appears to be lower than for the Taurus region, with only four sources beingdetected (three are attributable to disks). H2CO emission is found more frequently, but appears in general to be due tothe surrounding cloud. The weaker emission than in Taurus may suggest that the average disk size in the ρ Oph regionis smaller than in the Taurus cloud. Chemical modeling shows that the somewhat higher expected disk temperaturesin ρ Oph play a direct role in decreasing the CN abundance. Warmer dust temperatures contribute to convert CNinto less volatile forms. In such a young region, CN is no longer a simple, sensitive tracer of disks, and observationswith other tracers and at high enough resolution with ALMA are required to probe the gas disk population.

Accepted by A&A

http://arxiv.org/pdf/1504.04542

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Chemistry in Protoplanetary Disks: the gas-phase CO/H2 ratio and the Carbon reser-voir

L. Reboussin1,2, V. Wakelam1,2, S. Guilloteau1,2, F. Hersant1,2 and A. Dutrey1,2

1 Universite de Bordeaux, LAB, UMR 5804, F-33270, Floirac, France2 CNRS, LAB, UMR 5804, F-33270, Floirac, France

E-mail contact: laura.reboussin at obs.u-bordeaux1.fr

The gas mass of protoplanetary disks, and the gas-to-dust ratio, are two key elements driving the evolution of thesedisks and the formation of planetary system. We explore here to what extent CO (or its isotopologues) can be usedas a tracer of gas mass. We use a detailed gas-grain chemical model and study the evolution of the disk composition,starting from a dense pre-stellar core composition. We explore a range of disk temperature profiles, cosmic raysionization rates, and disk ages for a disk model representative of T Tauri stars. At the high densities that prevail indisks, we find that, due to fast reactions on grain surfaces, CO can be converted to less volatile forms (principallys-CO2, and to a lesser extent s-CH4) instead of being evaporated over a wide range of temperature. The canonicalgas-phase abundance of 10−4 is only reached above about 30-35 K. The dominant Carbon bearing entity dependson the temperature structure and age of the disk. The chemical evolution of CO is also sensitive to the cosmic raysionization rate. Larger gas phase CO abundances are found in younger disks. Initial conditions, such as parent cloudage and density, have a limited impact. This study reveals that CO gas-phase abundance is heavily dependent on grainsurface processes, which remain very incompletely understood so far. The strong dependence on dust temperatureprofile makes CO a poor tracer of the gas-phase content of disks.

Accepted by A&A

http://arxiv.org/pdf/1505.01309

A Catalog of Point Sources Towards NGC 1333

L. M. Rebull1

1 Infrared Science Archive (IRSA) and Spitzer Science Center (SSC), Infrared Processing and Analysis Center (IPAC)

E-mail contact: rebull at ipac.caltech.edu

I present a catalog of point source objects towards NGC 1333, resolving a wide variety of confusion about source names(and occasionally positions) in the literature. I incorporate data from optical to radio wavelengths, but focus mostof the effort on being complete and accurate from J (1.25 µm) to 24 µm. The catalog encompasses 52◦ <RA< 52.5◦

and 31◦ <Dec< 31.6◦. Cross-identifications include those from more than 25 papers and catalogs from 1994-2014,primarily those in wide use as origins of nomenclature. Gaps in our knowledge are identified, with the most importantbeing a lack of spectroscopy for spectral types or even confirmation of youth and/or cluster membership. I fit a slopeto the spectral energy distribution (SED) between 2 and 24 µm for the members (and candidate members) to obtainan SED classification, and compare the resulting classes to those for the same sources in the literature, and for an SEDfit between 2 and 8 µm. While there are certainly differences, for the majority of the sources, there is good agreement.

Accepted by AJ

http://arxiv.org/pdf/1504.07564

HH 666: Different kinematics from Hα and [Fe II] emission provide a missing linkbetween jets and outflows

Megan Reiter1, Nathan Smith1, Megan M. Kiminki1, and John Bally2

1 Steward Observatory, University of Arizona, Tucson, 933 N. Cherry Ave, Tucson, AZ 85721, USA2 Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309, USA

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

HH 666 is an externally irradiated protostellar outflow in the Carina Nebula for which we present new near-IR [FeII] spectra obtained with the FIRE spectrograph at Magellan Observatory. Earlier Hα and near-IR [Fe II] imagingrevealed that the two emission lines trace substantially different morphologies in the inner ∼40′′ of the outflow. Hα

34

traces a broad cocoon that surrounds the collimated [Fe II] jet that extends throughout the parent dust pillar. Newspectra show that this discrepancy extends to their kinematics. Near-IR [Fe II] emission traces steady, fast velocitiesof ±200 km s−1 from the eastern and western limbs of the jet. We compare this to a previously published Hα spectrumthat reveals a Hubble-flow velocity structure near the jet-driving source. New, second-epoch HST/ACS Hα imagesreveal the lateral spreading of the Hα outflow lobe away from the jet axis. Hα proper motions also indicate a suddenincrease in the mass-loss rate ∼1000 yr ago, while steady [Fe II] emission throughout the inner jet suggests that theburst is ongoing. An accretion burst sustained for ∼1000 yr is an order of magnitude longer than expected for FUOrionis outbursts, but represents only a small fraction of the total age of the HH 666 outflow. Altogether, availabledata suggests that [Fe II] traces the highly collimated protostellar jet while Hα traces the entrained and irradiatedoutflow. HH 666 appears to be a missing link between bare jets seen in H II regions and entrained molecular outflowsseen from embedded protostars in more quiescent regions.

Accepted by MNRAS

http://arxiv.org/pdf/1504.00669

Near-Infrared Variability in the Orion Nebula Cluster

Thomas S. Rice1, Bo Reipurth2, Scott J. Wolk3, Luiz Paulo Vaz4, and N. J. G. Cross5

1 Department of Astronomy, University of Michigan, 311 West Hall, 1085 South University Avenue, Ann Arbor, MI48109, USA2 Institute for Astronomy at Manoa and NASA Astrobiology Institute, University of Hawaii, 640 N. Aohoku Place,Hilo, HI 96720, USA3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA4 Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, C.P. 702, 30.123-970, Belo Horizonte, MG,Brazil5 Scottish Universities Physics Alliance, Institute for Astronomy, School of Physics, University of Edinburgh, RoyalObservatory, Blackford hill, Edinburgh, EH( 3HJ, UK

E-mail contact: tsrice at umich.edu

Using the United Kingdom Infrared Telescope on Mauna Kea, we have carried out a new near-infrared J, H, Kmonitoring survey of almost a square degree of the star-forming Orion Nebula Cluster with observations on 120 nightsover three observing seasons, spanning a total of 894 days. We monitored ∼15,000 stars down to J∼20 using theWFCAM instrument, and have extracted 1203 significantly variable stars from our data. By studying variability inyoung stellar objects (YSOs) in the H–K, K color-magnitude diagram, we are able to distinguish between physicalmechanisms of variability. Many variables show color behavior indicating either dust-extinction or disk/accretionactivity, but we find that when monitored for longer periods of time, a number of stars shift between these twovariability mechanisms. Further, we show that the intrinsic timescale of disk/accretion variability in young stars islonger than that of dust-extinction variability. We confirm that variability amplitude is statistically correlated withevolutionary class in all bands and colors. Our investigations of these 1203 variables have revealed 73 periodic AATau type variables, many large-amplitude and long-period (P > 15 day) YSOs, including three stars showing widely-spaced periodic brightening events consistent with circumbinary disk activity, and four new eclipsing binaries. Thesephenomena and others indicate the activity of long-term disk/accretion variability processes taking place in youngstars. We have made the light curves and associated data for these 1203 variables available online.

Accepted by Astron. J.

http://arxiv.org/pdf/1505.01495

On shocks driven by high-mass planets in radiatively inefficient disks. I. Two-dimensionalglobal disk simulations

Alexander J.W. Richert1,2,3,4, Wladimir Lyra3,4,5, Aaron Boley6, Mordecai-Mark Mac Low7, NealTurner3

1 Department of Astronomy & Astrophysics, Penn State University, 525 Davey Lab, University Park, PA 16802, USA2 Center for Exoplanets & Habitable Worlds, Pennsylvania State University

35

3 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA4 Division of Geological & Planetary Sciences, California Institute of Technology, 1200 E California Blvd MC 150-21,Pasadena, CA 91125 USA5 Sagan Fellow6 Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BCV6T 1Z1, Canada7 Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York,NY 10024-5192, USA

E-mail contact: ajr327 at psu.edu

Recent observations of gaps and non-axisymmetric features in the dust distributions of transition disks have been inter-preted as evidence of embedded massive protoplanets. However, comparing the predictions of planet-disk interactionmodels to the observed features has shown far from perfect agreement. This may be due to the strong approximationsused for the predictions. For example, spiral arm fitting typically uses results that are based on low-mass planetsin an isothermal gas. In this work, we describe two-dimensional, global, hydrodynamical simulations of disks withembedded protoplanets, with and without the assumption of local isothermality, for a range of planet-to-star massratios 1–10 Mjup for a 1 M⊙ star. We use the Pencil Code in polar coordinates for our models. We find that theinner and outer spiral wakes of massive protoplanets (M > 5 Mjup) produce significant shock heating that can triggerbuoyant instabilities. These drive sustained turbulence throughout the disk when they occur. The strength of thiseffect depends strongly on the mass of the planet and the thermal relaxation timescale; for a 10 Mjup planet embeddedin a thin, purely adiabatic disk, the spirals, gaps, and vortices typically associated with planet-disk interactions aredisrupted. We find that the effect is only weakly dependent on the initial radial temperature profile. The spirals thatform in disks heated by the effects we have described may fit the spiral structures observed in transition disks betterthan the spirals predicted by linear isothermal theory.

Accepted by ApJ

http://arxiv.org/pdf/1504.00066

Herschel SPIRE-FTS observations of RCW 120

J.A. Rodon1,2, A. Zavagno2, J.-P. Baluteau2, E. Habart3, M. Kohler3, J. Le Bourlot4, F. Le Petit4, andA. Abergel3

1 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago 19, Chile2 Aix Marseille universite, CNRS, Laboratoire d’Astrophysique de Marseille, UMR 7326, 13388 Marseille, France3 Institut d’Astrophysique Spatiale, CNRS/Universite Paris-Sud 11, 91405 Orsay, France4 LUTH, Observatoire de Paris et Universite Paris 7, 5 Place Jules Janssen, F-92190 Meudon, France

E-mail contact: jrodon at eso.org

The expansion of Galactic HII regions can trigger the formation of a new generation of stars. However, little isknow about the physical conditions that prevail in these regions. We study the physical conditions that prevail inspecific zones towards expanding HII regions that trace representative media such as the photodissociation region, theionized region, and condensations with and without ongoing star formation. We use the SPIRE Fourier TransformSpectrometer (FTS) on board Herschel to observe the HII region RCW 120. Continuum and lines are observed inthe 190–670 µm range. Line intensities and line ratios are obtained and used as physical diagnostics of the gas. Weused the Meudon PDR code and the RADEX code to derive the gas density and the radiation field at nine distinctpositions including the PDR surface and regions with and without star-formation activity. For the different regionswe detect the atomic lines [NII] at 205 µm and [CI] at 370 and 609 µm, the 12CO ladder between the J=4 and J=13levels and the 13CO ladder between the J=5 and J=14 levels, as well as CH+ in absorption. We find gas temperaturesin the range 45–250K for densities of 104–106 cm−3, and a high column density on the order of NH ∼ 1022 cm−2

that is in agreement with dust analysis. The ubiquitousness of the atomic and CH+ emission suggests the presenceof a low-density PDR throughout RCW 120. High-excitation lines of CO indicate the presence of irradiated densestructures or small dense clumps containing young stellar objects, while we also find a less dense medium (NH ∼ 1020

cm−2) with high temperatures (80–200K).

Accepted by A&A

http://arxiv.org/pdf/1504.06485

36

The Kinematic and Chemical Properties of a Potential Core-Forming Clump: PerseusB1-E

S.I. Sadavoy1, Y. Shirley2,1, J. Di Francesco3, Th. Henning1, M.J. Currie4, Ph. Andre5, S. Pezzuto6

1 Max-Planck-Institut fur Astronomie (MPIA), Konigstuhl 17, D-69117 Heidelberg, Germany2 Astronomy Department, The University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721, USA3 National Research Council Canada, 5071 West Saanich Road, Victoria BC Canada, V9E 2E74 Joint Astronomy Centre, 660 N. Aohoku Place, University Park, Hilo, Hawaii, 96720, USA5 Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/Service dAstrophysique, Saclay, 91191 Gifsur-Yvette, France6 Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, 00133, Rome, Italy

E-mail contact: sadavoy at mpia.de

We present 13CO and C18O (1–0), (2–1), and (3–2) maps towards the core-forming Perseus B1-E clump using ob-servations from the James Clerk Maxwell Telescope (JCMT), Submillimeter Telescope (SMT) of the Arizona RadioObservatory, and IRAM 30 m telescope. We find that the 13CO and C18O line emission both have very complexvelocity structures, indicative of multiple velocity components within the ambient gas. The (1–0) transitions reveala radial velocity gradient across B1-E of 1 km s−1 pc−1 that increases from north-west to south-east, whereas themajority of the Perseus cloud has a radial velocity gradient increasing from south-west to north-east. In contrast, wesee no evidence of a velocity gradient associated with the denser Herschel-identified substructures in B1-E. Addition-ally, the denser substructures have much lower systemic motions than the ambient clump material, which indicatesthat they are likely decoupled from the large-scale gas. Nevertheless, these substructures themselves have broad linewidths (0.4 km s−1) similar to that of the C18O gas in the clump, which suggests they inherited their kinematicproperties from the larger-scale, moderately dense gas. Finally, we find evidence of C18O depletion only toward onesubstructure, B1-E2, which is also the only object with narrow (transonic) line widths. We suggest that as prestellarcores form, their chemical and kinematic properties are linked in evolution, such that these objects must first dissipatetheir turbulence before they deplete in CO.

Accepted by ApJ

http://arxiv.org/pdf/1504.05206

High spectral and spatial resolution observations of the PDR emission in the NGC2023reflection nebula with SOFIA and APEX

G. Sandell1, B. Mookerjea2, R. Gusten3, M. A. Requena-Torres3, D. Riquelme3 and Y. Okada4

1 SOFIA/USRA, NASA Ames Research Center, MS 232-12, Building N232, Rm. 146, PO Box 1, Moffett Field, CA94035-0001, USA2 Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India3 Max Planck Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany4 I. Physikalisches Institut der Universitat zu Koln, Zulpicher Straße 77, 50937 Koln, Germany

E-mail contact: gsandell at sofia.usra.edu

We have mapped the NGC 2023 reflection nebula in [C ii] and CO(11–10) with the heterodyne receiver GREAT onSOFIA and obtained slightly smaller maps in 13CO(3–2), CO(3–2), CO(4–3), CO(6–5), and CO(7–6) with APEXin Chile. We use these data to probe the morphology, kinematics, and physical conditions of the C ii region, whichis ionized by FUV radiation from the B2 star HD37903. The [C ii] emission traces an ellipsoidal shell-like regionat a position angle of ∼ −50◦, and is surrounded by a hot molecular shell. In the southeast, where the C ii regionexpands into a dense, clumpy molecular cloud ridge, we see narrow and strong line emission from high-J CO lines,which comes from a thin, hot molecular shell surrounding the [C ii] emission. The [C ii] lines are broader and showphoto evaporating gas flowing into the C ii region. Based on the strength of the [13C ii] F=2–1 line, the [C ii] lineappears to be somewhat optically thick over most of the nebula with an optical depth of a few. We model the physicalconditions of the surrounding molecular cloud and the PDR emission using both RADEX and simple PDR models.The temperature of the CO emitting PDR shell is ∼ 90 – 120 K, with densities of 105 – 106 cm−3, as deduced fromRADEX modeling. Our PDR modeling indicates that the PDR layer where [C ii] emission dominates has somewhatlower densities, 104 to a few times 105 cm−3.

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Accepted by Astronomy & Astrophysics

http://arxiv.org/pdf/1504.03745

The young low-mass star ISO-Oph-50: Extreme variability induced by a clumpy, evolv-ing circumstellar disk

Alexander Scholz1, Koraljka Muzic2, Vincent Geers3

1 School of Physics and Astronomy, University of St. Andrews, The North Haugh, St. Andrews, Fife, KY16 9SS,United Kingdom2 European Southern Observatory, Alonso de Cordova 3107, Casilla 19, Santiago 19001, Chile3 UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UnitedKingdom

E-mail contact: as110 at st-andrews.ac.uk

ISO-Oph-50 is a young low-mass object in the ∼1 Myr old Ophiuchus star forming region undergoing dramatic changesin its optical/near/mid-infrared brightness by 2–4 mag. We present new multi-band photometry and near-infraredspectra, combined with a synopsis of the existing literature data. Based on the spectroscopy, the source is confirmedas a mid M dwarf, with evidence for ongoing accretion. The near-infrared lightcurves show large-scale variations, with2–4 mag amplitude in the bands IJHK, with the object generally being bluer when faint. Near its brightest state, theobject shows colour changes consistent with variable extinction of ∆AV ∼ 7 mag. High-cadence monitoring at 3.6 µmreveals quasi-periodic variations with a typical timescale of 1–2 weeks. The best explanation for these characteristics isa low-mass star seen through circumstellar matter, whose complex variability is caused by changing inhomogeneities inthe inner parts of the disk. When faint, the direct stellar emission is blocked; the near-infrared radiation is dominatedby scattered light. When bright, the emission is consistent with a photosphere strongly reddened by circumstellardust. Based on the available constraints, the inhomogeneities have to be located at or beyond ∼0.1 AU distance fromthe star. If this scenario turns out to be correct, a major portion of the inner disk has to be clumpy, structured, and/orin turmoil. In its observational characteristics, this object resembles other types of YSOs with variability caused inthe inner disk. Compared to other objects, however, ISO-Oph-50 is clearly an extreme case, given the large amplitudeof the brightness and colour changes combined with the erratic behaviour. ISO-Oph-50 has been near its brighteststate since 2013; further monitoring is highly encouraged.

Accepted by MNRAS

http://arxiv.org/pdf/1504.03568

Evolution of column density distributions within Orion A

A. M. Stutz1 and J. Kainulainen1

1 MPIA, Heidelberg, Germany

E-mail contact: stutz at mpia.de

We compare the structure of star–forming molecular clouds in different regions of Orion A to determine how the columndensity probability distribution function (N–PDF) varies with environmental conditions such as the fraction of youngprotostars. A correlation between the N–PDF slope and Class 0 protostar fraction has been previously observed in alow-mass star–formation region (Perseus) by Sadavoy; here we test if a similar correlation is observed in a high–massstar–forming region. We use Herschel PACS and SPIRE cold dust emission observations to derive a column density mapof Orion A. We use the Herschel Orion Protostar Survey (HOPS) catalog for accurate identification and classificationof the Orion A young stellar object (YSO) content, including the cold and relatively short–lived Class 0 protostars(with a ∼ 0.14 Myr lifetime). We divide Orion A into eight independent 0.25 square degree (13.5 pc2) regions; in eachregion we fit the N–PDF distribution with a power–law, and we measure the fraction of Class 0 protostars. We usea maximum likelihood method to measure the N–PDF power–law index without binning the column density data.We find that the Class 0 fraction is higher in regions with flatter column density distributions. We test the effectsof incompleteness, extinction–driven misclassification of Class 0 sources, resolution, and adopted pixel–scales. Weshow that these effects cannot account for the observed trend. Our observations demonstrate an association betweenthe slope of the power–law N–PDF and the Class 0 fractions within Orion A. Various interpretations are discussed

38

including timescales based on the Class 0 protostar fraction assuming a constant star–formation rate. The observedrelation suggests that the N–PDF can be related to an “evolutionary state” of the gas. If universal, such a relationpermits an evaluation of the evolutionary state from the N–PDF power–law index at much greater distances thanthose accesible with protostar counts.

Accepted by A&A Letters

http://arxiv.org/pdf/1504.05188

Constraining the abundances of complex organics in the inner regions of solar-typeprotostars

Vianney Taquet1,2, Ana Lpez-Sepulcre3,4,5, Cecilia Ceccarelli3,4, Roberto Neri6, Claudine Kahane3,4

and Steven B. Charnley1

1 Astrochemistry Laboratory and The Goddard Center for Astrobiology, Mailstop 691, NASA Goddard Space FlightCenter, USA2 Leiden Observatory, Leiden University, The Netherlands3 Univ. Grenoble Alpes, France4 CNRS, IPAG, France5 Department of Physics, The University of Tokyo, Japan6 Institut de Radioastronomie Millimtrique, Grenoble, France

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

The high abundances of Complex Organic Molecules (COMs) with respect to methanol, the most abundant COM,detected toward low-mass protostars, tend to be underpredicted by astrochemical models. This discrepancy mightcome from the large beam of the single-dish telescopes, encompassing several components of the studied protostar,commonly used to detect COMs. To address this issue, we have carried out multi-line observations of methanol andseveral COMs toward the two low-mass protostars NGC 1333-IRAS 2A and -IRAS 4A with the Plateau de Bureinterferometer at an angular resolution of 2??, resulting in the first multi-line detection of the O-bearing speciesglycolaldehyde and ethanol and of the N-bearing species ethyl cyanide toward low-mass protostars other than IRAS16293. The high number of detected transitions from COMs (more than 40 methanol transitions for instance) allowedus to accurately derive the source size of their emission and the COM column densities. The COM abundances withrespect to methanol derived toward IRAS 2A and IRAS 4A are slightly, but not substantially, lower than those derivedfrom previous single-dish observations. The COM abundance ratios do not vary significantly with the protostellarluminosity, over five orders of magnitude, implying that low-mass hot corinos are quite chemically rich as high-masshot cores. Astrochemical models still underpredict the abundances of key COMs, such as methyl formate or di-methylether, suggesting that our understanding of their formation remains incomplete.

Accepted by The Astrophysical Journal

http://iopscience.iop.org/0004-637X/804/2/81/

Gas density drops inside dust cavities of transitional disks around young stars observedwith ALMA

Nienke van der Marel1, Ewine F. van Dishoeck1,2, Simon Bruderer2, Laura Perez3 and Andrea Isella4

1 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, the Netherlands2 MPE, Giessenbachstrasse 1, 85748 Garching, Germany3 NRAO, P.O. Box O, Socorro, NM 87801, USA4 Rice University, 6100 Main Street, Houston, TX 77005, USA

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

Transitional disks with large dust cavities are important laboratories to study planet formation and disk evolution.Cold gas may still be present inside these cavities, but the quantification of this gas is challenging. The gas content isimportant to constrain the origin of the dust cavity. We use Atacama Large Millimeter/submillimeter Array (ALMA)observations of 12CO 6–5 and 690 GHz (Band 9) continuum of five well-studied transitional disks. In addition, weanalyze previously published Band 7 observations of a disk in 12CO 3–2 line and 345 GHz continuum. The observations

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are used to set constraints on the gas and dust surface density profiles, in particular the drop delta-gas of the gasdensity inside the dust cavity. The physical-chemical modeling code DALI is used to analyze the gas and dust imagessimultaneously. We model SR21, HD135344B, LkCa15, SR24S and RXJ1615-3255 (Band 9) and J1604-2130 (Band7). The SED and continuum visibility curve constrain the dust surface density. Subsequently, the same model isused to calculate the 12CO emission, which is compared with the observations through spectra and intensity cuts.The amount of gas inside the cavity is quantified by varying the delta-gas parameter. Model fits to the dust and gasindicate that gas is still present inside the dust cavity for all disks but at a reduced level. The gas surface densitydrops inside the cavity by at least a factor 10, whereas the dust density drops by at least a factor 1000. Disk massesare comparable with previous estimates from the literature, cavity radii are found to be smaller than in the 345 GHzSubMillimeter Array (SMA) data. The derived gas surface density profiles suggest clearing of the cavity by one ormore companions in all cases, trapping the millimeter-sized dust at the edge of the cavity.

Accepted by A&A

http://arxiv.org/pdf/1504.03927

Investigating the rotational evolution of young, low-mass stars using Monte Carlo sim-ulations

Maria Jaqueline Vasconcelos1,2 and Jerome Bouvier2

1 LATO/DCET - UESC, Rodovia Jorge Amado, km 16, Ilheus, 45662-900 - Brazil2 Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France CNRS, IPAG, F-38000 Grenoble, France

E-mail contact: mjvasc at uesc.br

Young stars rotate well below break-up velocity, which is thought to result from the magnetic coupling with theiraccretion disk. We investigate the rotational evolution of young stars under the disk-locking hypothesis throughMonte Carlo simulations. Our simulations included 280,000 stars, each of which was initially assigned a mass, arotational period, and a mass accretion rate. The mass accretion rate depends on both mass and time, followingpower-law indices of 1.4 and -1.5, respectively. A mass-dependent accretion threshold was defined below which astar was considered as diskless, which resulted in a distribution of disk lifetimes that matches observations. Starswere evolved at constant angular spin rate while accreting and at constant angular momentum when they becamediskless. Starting with a bimodal distribution of periods for disk and diskless stars, we recovered the bimodal perioddistribution seen in several young clusters. The short-period peak mostly consists of diskless stars, and the long-periodpeak is mainly populated by accreting stars. Both distributions, however, present a long tail toward long periods,and a population of slowly rotating diskless stars is observed at all ages. We reproduced the observed correlationsbetween disk fraction and spin rate, as well as between IR excess and rotational period. The period-mass relationwe derived from the simulations only shows the same global trend as observed in young clusters when we releasedthe disk-locking assumption for the lowest mass stars. Finally, we find that the time evolution of median specificangular momentum follows a power-law index of -0.65 for accreting stars, as expected from disk locking, and of -0.53for diskless stars, a shallower slope that results from a wide distribution of disk lifetimes. At the end of the accretionphase, our simulations reproduce the angular momentum distribution of the low-mass members of the 13 Myr h Percluster. Using observationally documented distributions of disk lifetimes, mass accretion rates, and initial rotationperiods, and evolving an initial population from 1 to 12 Myr, we reproduced the main characteristics of pre-mainsequence angular momentum evolution, which supports the disk-locking hypothesis.

Accepted by Astronomy & Astrophysics

http://arxiv.org/pdf/1504.04717

Strong effect of the cluster environment on the size of protoplanetary discs?

Kirsten Vincke1, Andreas Breslau1 and Susanne Pfalzner1

1 Max Planck Institute for Radio Astronomy, Auf dem Hugel 69, 53121 Bonn, Germany

E-mail contact: kvincke at mpifr-bonn.mpg.de

Context. Most stars are born in clusters, thus the protoplanetary discs surrounding the newly formed stars might beinfluenced by this environment. Isolated star-disc encounters have previously been studied, and it was shown that

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very close encounters are necessary to completely destroy discs. However, relatively distant encounters are still ableto change the disc size considerably.Aims. We quantify the importance of disc-size reduction that is due to stellar encounters in an entire stellar population.Method. We modelled young, massive clusters of different densities using the code Nbody6 to determine the statistics ofstellar encounter parameters. In a second step, we used these parameters to investigate the effect of the environmentson the disc size. For this purpose, we performed a numerical experiment with an artificial initial disc size of 105 AU.Results. We quantify to which degree the disc size is more sensitive to the cluster environment than to the disc massor frequency. We show that in all investigated clusters a large portion of discs is significantly reduced in size. After5 Myr, the fraction of discs smaller than 1000 AU in ONC-like clusters with an average number density of ∼ 60 pc−3,the fraction of discs smaller than 1000 AU is 65%, while discs smaller than 100 AU make up 15%. These fractionsincrease to 84% and 39% for discs in denser clusters like IC 348 (∼ 500 pc−3). Even in clusters with a density fourtimes lower than in the ONC (∼ 15 pc−3), about 43% of all discs are reduced to sizes below 1000 AU and roughly 9%to sizes below 100 AU.Conclusions. For any disc in the ONC that initially was larger than 1000 AU, the probability to be truncated tosmaller disc sizes as a result of stellar encounters is quite high. Thus, among other effects, encounters are importantin shaping discs and potentially forming planetary systems in stellar clusters.

Accepted by Astronomy & Astrophysics

http://arxiv.org/pdf/1504.06092

Spectro-astrometry of LkCa 15 with X-Shooter: Searching for emission from LkCa 15b

E.T. Whelan1, N. Huelamo2, J.M. Alcala3,J. Lillo-Box2, H. Bouy2, D. Barrado2, J. Bouvier4,5, and B.Merın6

1 Institut fur Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Eberhard Karls Universitat,72076 Tubingen, Germany 2 Centro de Astrobiologıa, INTA-CSIC, Depto Astrofısica, European Space AstronomyCente (ESAC) Campus, PO Box 78, 28691, Villanueva de la Canada, Madrid, Spain3 INAF-Osservatorio Astronomico di Capodimonte, via Moiariello, 16, I-80131, Napoli, Italy4 Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France5 CNRS, IPAG, F-38000 Grenoble, France6 European Space Astronomy Center (ESAC), P.O. box 78, 28691, Villanueva de la Caada, Madrid, Spain

E-mail contact: emma.whelan at astro.uni-tuebingen.de

Planet formation is one explanation for the partial clearing of dust observed in the disks of some T Tauri stars.Indeed studies using state-of-the-art high angular resolution techniques have very recently begun to observe planetarycompanions in these so-called transitional disks. The goal of this work is to use spectra of the transitional disk objectLkCa 15 obtained with X-Shooter on the Very Large Telescope to investigate the possibility of using spectro-astrometryto detect planetary companions to T Tauri stars. It is argued that an accreting planet should contribute to the totalemission of accretion tracers such as Hα and therefore planetary companions could be detected with spectro-astrometryin the same way as it has been used to detect stellar companions to young stars. A probable planetary-mass companionwas recently detected in the disk of LkCa 15. Therefore, it is an ideal target for this pilot study. We studied severalkey accretion lines in the wavelength range 300 nm to 2.2 µm with spectro-astrometry. While no spectro-astrometricsignal is measured for any emission lines the accuracy achieved in the technique is used to place an upper limit on thecontribution of the planet to the flux of the Hα, Paγ, and Paβ lines. The derived upper limits on the flux allows anupper limit of the mass accretion rate, log(Macc) = −8.9 to −9.3 for the mass of the companion between 6 MJup and15 MJup, respectively, to be estimated (with some assumptions).

Accepted by A&A

http://arxiv.org/pdf/1504.04824

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New Jobs

New Faculty Position in Galactic or Extragalactic Star Formation atUniversidad de Chile

The Universidad de Chile Department of Astronomy (DAS) invites applications for a tenure track position at theassistant professor level beginning no later than September 2016. We are primarily interested in candidates with aproven record of independent research in the area of star formation, in the Galactic and/or extragalactic fields. Inparticular, we seek candidates who can make effective use of the 10% of ALMA time available to astronomers workingin Chilean institutions.

The successful candidate is expected to join the activities of the DAS, including carrying out an original researchprogram involving graduate students and postdocs, and teaching at the graduate and undergraduate levels. Graduatelevel teaching is often conducted in English, however, candidates are expected to teach undergraduate courses inSpanish after 1 year of arrival. Spanish courses for foreigners are offered for free by the University.

Our department is one of the leading –and the oldest– astronomy centers in Chile, fostering an engaging and productiveinternational community composed of 22 faculty, 15 postdoctoral researchers, and 30 graduate students. The DAShosts many international programs including the French UMI-FCA, the Chinese CASSACA (www.cassaca.org), andother major science and technology grants (see www.das.uchile.cl/web en/das proyectos.html).

The successful applicant will have access to the 10% of telescope time guaranteed to Chilean institutions on allobservatories in the country, including the future GMT and E-ELT (see www.das.uchile.cl/das cntac.html). Super-computing facilities are available both locally and through the National Laboratory for High Performance Computing(www.nlhpc.cl).

Interested applicants should submit a curriculum vitae, a list of publications, a statement of previous research (3 pagelimit), a research plan (5 page limit), and a description of teaching interests (1 page). At least three letters of referenceshould be sent directly to the recruiting committee. All materials must be emailed to newfaculty@das.uchile.cl. Reviewof the applications will commence on July 1st, 2015 and will continue until the position is filled. We expect to havea short list by the end of September and to make an offer before the end of November 2015. For enquiries, pleasecontact Diego Mardones, chair of the recruiting committee, at diego@das.uchile.cl.

Santiago is a growing metropolis with excellent global communications and a high standard of living. The DAS islocated in a beautiful part of the city, site of the old National Observatory. The compensation package includes acompetitive salary, moving expenses, and housing benefits. Chilean law includes six months of paid parental leave formothers.

Universidad de Chile is an equal opportunity employer committed to excellence through diversity. We encourageapplications from all nationalities and from under-represented groups in science.

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Postdoctoral and PhD position in protoplanetary/debris discs orevolved stars with planets at the UAM, Madrid, Spain

Applications are invited for a 2-year postdoctoral position (1+1yr after positive evaluation) and a 4-year PhD positionat the Department of Theoretical Physics from the Universidad Autonoma de Madrid (UAM). The successful candi-dates will be hired under the project ”From stones to planets and back to rocks: understanding planet formation anddestruction” (AYA2014-55840-P), lead by Eva Villaver and Gwendolyn Meeus and funded by the Spanish NationalPlan of R&D. The research will depend on the experience of the candidate, but should focus on either:

- How the structure of protoplanetary and debris discs depends on the presence of planets.

- How stellar evolution affects the architecture of planetary systems.

The methods can either be observational or theoretical. For the postdoctoral position, we are seeking a highlymotivated researcher with experience in some of the following areas: protoplanetary or debris disc modelling, stellarevolution, detection of planets, or high spatial/spectral resolution disc observations (e.g. with ALMA, SPHERE orNACO).

Postdoctoral applicants must have obtained their PhD in Astrophysics or Physics and have a doctoral certificate atthe moment of appointment, while the doctoral candidate must have a Master in Astrophysics or Physics at that time.Ideally the position will start in fall of 2015, but a later start is also possible. Applicants should send their CV withpublication list, along with a cover letter briefly describing research interests and achievements, and arrange for tworecommendation letters to be sent to eva.villaver@uam.es and gwendolyn.meeus@uam.es by July 20th, 2015.

The contracts include medical insurance under the Spanish National Health Service which also cover your accompanyingpartner and children, if relevant.

Our group is also a host for Marie S. Curie fellowships, and can provide administrative support for those wishing toapply.

Located in Madrid, Spain, the Department of Theoretical Physics at UAM offers a rich atmosphere in front-linephysics research, ranging from Particle Physics (both theoretical and experimental), Nuclear Physics, Neuroscience,Experimental High-Energy Physics, to Astrophysics. The Astrophysics group at the department carries out researchon Cosmology, Galactic and Extra-galactic Astrophysics, and runs a Master PhD program in Astrophysics. Fur-ther information about UAM’s Department of Theoretical Physics is available via the Internet on the UAM Webpage (www.ft.uam.es). Close collaboration with the Centre for Astrobiology (CAB) and the ESA European SpaceAstronomy Centre (ESAC), also located in Madrid, is ongoing.

PhD position on the origin of the IMFVienna, Austria

Given our group’s recent success in calibrating ESA Herschel Space Observatory data and constructing robust andlarge-scale column density and temperature maps of nearby stellar nurseries, we are looking for a PhD candidate toexplore the possible link between molecular cloud structure and the origin of the stellar Initial Mass Function (IMF).The candidate will work on a robust definition of a dense core, the ’stellar embryo’, a fundamental but hard to defineastrophysical object, as well as on the optimal extraction techniques from large scale dust continuum maps and corepopulation statistics. We are looking for a highly motivated PhD student with a good knowledge of image analysisand statistics (preferably with open source tools, e.g., Python, R) and familiarity with interstellar cloud research.

The Department of Astrophysics of the University of Vienna offers a stimulating research environment with staffworking in various areas of astrophysics. The department is involved in the major observatories of ESO (VLT andE-ELT) and ESA/JAXA/NASA (Gaia, Spica, Plato, Euclid, JWST). The city of Vienna, where E. Salpeter was born,scored highest worldwide for overall quality of living for 4 consecutive years according to Mercer’s survey (2010-2014).

Review of applications starts Jun 1st, 2015 and will continue until the position is filled. Applications should be sentto Prof. Joao Alves (joao.alves@univie.ac.at) and include: 1) CV, 2) a brief description of past research, and 3) twoletters of reference.

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Meetings

From Clouds to Protoplanetary Disks: the Astrochemical Link

5-8 October 2015Hans Harnack Haus, Berlin, Germany

Recent advances in sub-millimeter (ALMA, NOEMA) and IR (Spitzer, Herschel) observational facilities and modelinghave started to shed more light on the physical and chemical processes governing the evolution of interstellar cloudsinto pre-stellar cores, protostars, protoplanetary disks, and, eventually, planetary systems. Molecular spectroscopy hasplayed a crucial role in these advances, as only lines can unveil the underlying dynamics and can provide informationon the physical and chemical structure across clouds, cores and protoplanetary disks. Furthermore, chemo-dynamicalmodels have become more and more detailed, thanks also to the great advances in (gas phase and surface) laboratorywork as well as quantum chemistry calculations, while magneto-hydrodynamical simulations have included simplifiedchemical codes to test theoretical predictions. We believe this is the right moment to try to summarize a currentstatus quo in this exciting field of astronomy, and to facilitate and foster future directions of astrochemistry research.

Since astrochemistry is the trait d’union of different communities, the main goal of this well-focussed meeting will beto bring together observers, theoreticians and experimentalists to present their recent advances, to discuss about themain uncertainties and to plan future developments. Interaction between the different communities will be encouragedand mixed, lengthy discussions will be organized at the end of each session, and in the end of each conference’s day.We will particularly encourage young scientists (students, PhD students, post-docs) to participate, with the main aimto help them to shape their knowledge and understanding of modern and forthcoming ideas about details of planet-and star-formation from a cohort of the world-leading experts.

Further information can be found on the workshop website: https://cas-events.mpe.mpg.de/astrolink

SOC/LOC:Chair: Paola Caselli (MPE Garching Munchen)co-Chair: Dimitry Semenov (MPIA Heidelberg, co-Chair)Christian Endres (MPE Garching Munchen)Leonardo Testi (ESO Garching Munchen)Anton Vasyunin (MPE Garching Munchen)Yuri Aikawa (Kobe Univ., Japan)Henrik Beuther (MPIA Heidelberg, DE)Jrgen Blum (TU Braunschweig, DE)Cecilia Ceccarelli (IPAG, Grenoble, France)Ewine van Dishoeck (Leiden/ESO, NL/DE)Cornelis Dullemond (ITA Heidelberg, DE)Anne Dutrey (LAB, Bordeaux, France)Thomas Henning (MPIA Heidelberg, DE)Eric Herbst (Univ. of Virginia, Charlottesville, USA)Karin Oeberg (Harvard Univ., USA)Nami Sakai (Univ. of Tokio, Japan)Peter Schilke (MPIfR, Bonn, DE)Serena Viti (UCL, London, UK)

Organizer: MPE Garching & MPIA Heidelberg

The total number of participants is restricted by the available rooms in the Harnack-Haus and will be limited to 120guests.

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Cloudy workshop 2015 Sept 21-26 Inter-University Centre forAstronomy and Astrophysics, Pune, India

Registration is now open for the 2015 September Cloudy workshop. It will be held Sept 2126 at the Inter-UniversityCentre for Astronomy and Astrophysics (IUCAA), Pune, India

Cloudy simulates the microphysics of matter exposed to ionizing radiation. It calculates the atomic physics, chem-istry, radiation transport, and dynamics problems simultaneously and self consistently, building from a foundation ofindividual atomic and molecular processes. The result is a prediction of the conditions in the material and its observedspectrum.

The workshop will cover observation, theory, and application of Cloudy to a wide variety of astronomical environments.This includes the theory of diffuse non-LTE matter and quantitative spectroscopy, the science of using spectra to makephysical measurements. We will use Cloudy to simulate such objects as AGB stars, Active Galactic Nuclei, Starburstgalaxies, and the intergalactic medium.

The sessions will consist of a mix of textbook study, using Osterbrock & Ferland, Astrophysics of Gaseous Nebulaeand Active Galactic Nuclei, application of the spectral-simulation code Cloudy to a variety of astrophysical problems,and projects organized by the participants. No prior experience with Cloudy is assumed. There is no registration feeand financial support is not available.

See http://cloud9.pa.uky.edu/?gary/cloudy/CloudySummerSchool/ for more information and for information onhow to apply.

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Summary of Upcoming Meetings

Triple Evolution & Dynamics in Stellar and Planetary Systems31 May - 5 June 2015 Haifa, Israelhttp://trendy-triple.weebly.com

Workshop on the Formation of the Solar System II2 - 4 June 2015 Berlin, Germanyhttps://indico.mpifr-bonn.mpg/FormationOfTheSolarSystem2

IGM@50: is the Intergalactic medium driving Star Formation?8 - 12 June 2015 Abbazia di Spineto, Italyhttp://www.arcetri.astro.it/igm50

The Formation and Destruction of Molecular Clouds22 - 23 June 2015 Tenerife, Spainhttp://eas.unige.ch/EWASS2015/session.jsp?id=S6

30 Years of Photodissociation regions - A Symposium to honor David Hollenbach’s lifetime in science28 June - 3 July 2015http://pdr30.strw.leidenuniv.nl

Gordon Research Conference on Origins of Solar Systems28 June - 3 July 2015http://www.grc.org/programs.aspx?id=12345

Disc dynamics and planet formation29 June - 3 July 2015 Larnaka, Cyprushttp://www.star.uclan.ac.uk/discs2015

The Stellar IMF at Low Masses: A Critical Look at Variations and Environmental Dependencies29 June - 1 July 2015 Baltimore, Maryland, USAhttp://www.stsci.edu/institute/conference/stellar-imf/

From super-Earths to brown dwarfs: Who’s who29 June - 3 July 2015 Paris, Francehttp://www.iap.fr/col2015

Orion (un)plugged1-3 + 6-8 July 2015 Vienna, Austriahttps://www.univie.ac.at/alveslab/orion_unplugged/

From Interstellar Clouds to Star-forming Galaxies: Universal Processes?3 - 7 August 2015 http://astronomy2015.org/symposium_315

Cosmic Dust17 - 21 August 2015 Tokyo, Japanhttps://www.cps-jp.org/~dust/

6th Zermatt ISM Symposium: Conditions and Impact of Star Formation - From Lab to Space7 - 11 September 2015 Zermatt, Switzerlandhttp://www.astro.uni-koeln.de/zermatt2015

Cloudy Workshop21 - 26 September 2015 Pune, Indiahttp://cloud9.pa.uky.edu/?gary/cloudy/CloudySummerSchool/

From Clouds to Protoplanetary Disks: the Astrochemical Link

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5 - 8 October 2015 Berlin, Germanyhttps://cas-events.mpe.mpg.de/astrolink

Exchanging Mass, Momentum and Ideas: Connecting Accretion and Outflows in Young Stellar Objects27 - 29 October 2015 Noordwijk, The Netherlandshttp://www.cosmos.esa.int/web/accretion-outflow-workshop

Extreme Solar Systems III 29 November - 4 December 2015 Hawaii, USAhttp://ciera.northwestern.edu/Hawaii2015.php

From Stars to Massive Stars6 - 9 April 2016, Gainesville, Florida, USAhttp://conference.astro.ufl.edu/STARSTOMASSIVE/

The 19th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun6 - 10 June 2016 Uppsala, Swedenhttp://www.coolstars19.com

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

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Short Announcements

Fizeau exchange visitors program - special call for applications

Dear colleagues!

The Fizeau exchange visitors program in optical interferometry funds (travel and accommodation) visits of researchersto an institute of his/her choice (within the European Community) to perform collaborative work and training on one ofthe active topics of the European Interferometry Initiative. The visits will typically last for one month, and strengthenthe network of astronomers engaged in technical, scientific and training work on optical/infrared interferometry. Theprogram is open for all levels of astronomers (Ph.D. students to tenured staff). non-EU based missions will onlybe funded if considered essential by the Fizeau Committee. Applicants are strongly encouraged to seek also partialsupport from their home or host institutions.

IMPORTANT NOTE: This is a special call to support attendance of the 8th VLTI summer school:http://www.astro.uni-koeln.de/vltischool2015.Therefore no research plan and invitation letter from the host institution are required.The deadline for applications is May 30.

Further informations and application forms can be found at www.european-interferometry.eu and vltischool.sciencesconf.org

The program is funded by OPTICON/FP7.

Please distribute this message also to potentially interested colleagues outside of your community!

Looking forward to your applications,Josef Hron & Laszlo Mosoni(for the European Interferometry Initiative)

Electronic mail: fizeau@european-interferometry.eu

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.

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