characterizing k2 planet discoveries: a …lzeng/papers/apj_800_1_59.pdf13 instituto de...

The Astrophysical Journal 80059 (14pp) 2015 February 10 doi1010880004-637X800159Ccopy 2015 The American Astronomical Society All rights reserved

CHARACTERIZING K2 PLANET DISCOVERIES A SUPER-EARTH TRANSITINGTHE BRIGHT K DWARF HIP 116454

Andrew Vanderburg128 Benjamin T Montet1228 John Asher Johnson129 Lars A Buchhave1 Li Zeng1Francesco Pepe3 Andrew Collier Cameron4 David W Latham1 Emilio Molinari56 Stephane Udry3

Christophe Lovis3 Jaymie M Matthews7 Chris Cameron8 Nicholas Law9 Brendan P Bowler230 Ruth Angus110Christoph Baranec11 Allyson Bieryla1 Walter Boschin5 David Charbonneau1 Rosario Cosentino5

Xavier Dumusque1 Pedro Figueira1213 David B Guenther14 Avet Harutyunyan5 Coel Hellier15Rainer Kuschnig16 Mercedes Lopez-Morales1 Michel Mayor3 Giusi Micela17 Anthony F J Moffat1819

Marco Pedani5 David F Phillips1 Giampaolo Piotto56 Don Pollacco20 Didier Queloz21 Ken Rice22 Reed Riddle2Jason F Rowe2324 Slavek M Rucinski25 Dimitar Sasselov1 Damien Segransan3 Alessandro Sozzetti26

Andrew Szentgyorgyi1 Chris Watson27 and Werner W Weiss161 Harvard-Smithsonian Center for Astrophysics Cambridge MA 02138 USA avanderburgcfaharvardedu

2 California Institute of Technology Pasadena CA 91125 USA3 Observatoire Astronomique de lrsquoUniversite de Geneve 51 chemin des Maillettes CH-1290 Versoix Switzerland

4 SUPA School of Physics and Astronomy University of St Andrews North Haugh St Andrews Fife KY16 9SS UK5 INAF-Fundacion Galileo Galilei Rambla Jose Ana Fernandez Perez 7 E-38712 Brena Baja Spain

6 INAF-IASF Milano via Bassini 15 I-20133 Milano Italy7 University of British Columbia Vancouver BC V6T1Z1 Canada

8 Cape Breton University 1250 Grand Lake Road Sydney NS B1P 6L2 Canada9 University of North Carolina at Chapel Hill Chapel Hill NC 27599 USA

10 University of Oxford Oxford UK11 University of Hawailsquoi at Manoa Hilo HI 96720 USA

12 Centro de Astrofısica Universidade do Porto Rua das Estrelas 4150-762 Porto Portugal13 Instituto de Astrofısica e Ciencias do Espaco Universidade do Porto CAUP Rua das Estrelas PT4150-762 Porto Portugal

14 St Maryrsquos University Halifax NS B3H 3C3 Canada15 Astrophysics Group Keele University Staffordshire ST5 5BG UK

16 Institut fur Astronomie Universitat Wien Turkenschanzstrasse 17 A-1180 Wien Austria17 INAF-Osservatorio Astronomico di Palermo Piazza del Parlamento 1 I-90124 Palermo Italy

18 Univ de Montreal CP 6128 Succ Centre-Ville Montreal QC H3C 3J7 Canada19 Obs du mont Megantic Notre-Dame-des-Bois QC J0B 2E0 Canada

20 Department of Physics University of Warwick Gibbet Hill Road Coventry CV4 7AL UK21 Cavendish Laboratory J J Thomson Avenue Cambridge CB3 0HE UK

22 SUPA Institute for Astronomy Royal Observatory University of Edinburgh Blackford Hill Edinburgh EH93HJ UK23 SETI Institute 189 Bernardo Avenue Mountain View CA 94043 USA

24 NASA Ames Research Center Moffett Field CA 94035 USA25 University of Toronto 50 St George Street Toronto ON M5S 3H4 Canada

26 INAF-Osservatorio Astrofisico di Torino Via Osservatorio 20 I-10025 Pino Torinese Italy27 Astrophysics Research Centre School of Mathematics and Physics Queens University Belfast Belfast BT7 1NN UK

Received 2014 October 20 accepted 2014 December 12 published 2015 February 9

ABSTRACT

We report the first planet discovery from the two-wheeled Kepler (K2) mission HIP 116454 b The host starHIP 116454 is a bright (V = 101 K = 80) K1 dwarf with high proper motion and a parallax-based distanceof 552 plusmn 54 pc Based on high-resolution optical spectroscopy we find that the host star is metal-poor with[FeH] = minus016plusmn008 and has a radius R = 0716 plusmn 0024 R and mass M = 0775plusmn0027 M The star wasobserved by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in 2014 February Duringthe 9 days of observations K2 observed a single transit event Using a new K2 photometric analysis technique weare able to correct small telescope drifts and recover the observed transit at high confidence corresponding to aplanetary radius of Rp = 253 plusmn 018 Roplus Radial velocity observations with the HARPS-N spectrograph reveal a1182 plusmn 133 Moplus planet in a 91 day orbit consistent with the transit depth duration and ephemeris Follow-upphotometric measurements from the MOST satellite confirm the transit observed in the K2 photometry and providea refined ephemeris making HIP 116454 b amenable for future follow-up observations of this latest addition to thegrowing population of transiting super-Earths around nearby bright stars

Key words planets and satellites detection ndash techniques photometric

Supporting material FITS file

1 INTRODUCTION

After four years of nearly continuous photometric monitoringand thousands of planet discoveries (eg Borucki et al 2011

28 NSF Graduate Research Fellow29 David and Lucile Packard Fellow30 Caltech Joint Center for Planetary Astronomy Fellow

Howard et al 2012 Muirhead et al 2012 Batalha et al2013 Barclay et al 2013 Morton amp Swift 2014) the primaryKepler mission came to an end in 2013 May with the failureof the second of four reaction wheels used to stabilize thespacecraft Without at least three functioning reaction wheelsthe spacecraft is unable to achieve the fine pointing necessary forhigh photometric precision on the original target field However

1

The Astrophysical Journal 80059 (14pp) 2015 February 10 Vanderburg et al

an extended mission called K2 was enabled by pointing alongthe ecliptic plane and balancing the spacecraft against solarradiation pressure to mitigate the instability caused by the failedreaction wheels The recently extended K2 mission enablesrenewed opportunities for transit science on a new set of brighttarget stars albeit with somewhat reduced photometric precisioncompared to the original Kepler mission (Howell et al 2014)

Searching for transiting exoplanets around bright nearbystars is important because measuring the precise masses andradii of transiting planets allows for characterization of theirinterior structures and atmospheres (Charbonneau et al 2002Rogers 2014 Knutson et al 2014 Teske et al 2013 Kreidberget al 2014) This is particularly desirable for planets withmasses intermediate to those of the Earth and Uranus commonlyreferred to as super-Earths because no such planet exists in oursolar system (Valencia et al 2006) However while the radiiof Kepler planets are often measured to high precision (Ballardet al 2014) their masses are generally unknown because thehost stars are faint (V gt 12) and exposure times needed forradial velocity (RV) measurements are prohibitive for all but thebrightest Kepler planet candidates (eg Dumusque et al 2014Marcy et al 2014)

Preparations for the extended two-wheeled Kepler missionincluded a 9 day test of the new observing mode in February of2014 After the data were released to the public Vanderburg ampJohnson (2014 hereafter VJ14) presented a photometric reduc-tion technique that accounts for the motion of the spacecraftimproves photometric precision of raw K2 data by a factor of2ndash5 and enables photometric precision comparable to that ofthe original Kepler mission

While the data collected during the engineering test wereintended primarily as a test of the new spacecraft operatingmode an inspection of light curves produced with this techniquenonetheless revealed a single transit event in engineering datataken of HIP 116454 In this paper we provide an analysis ofthat light curve along with archival and follow-up spectroscopyarchival and adaptive optics imaging RV measurements fromthe HARPS-N spectrograph and photometric observations fromthe Wide Angle Search for Planets (WASP) survey and theMicrovariability and Oscillations of STars (MOST) space tele-scope These measurements allow us to verify and characterizethe first planet discovered by the two-wheeled Kepler missiona new transiting super-Earth orbiting the bright nearby high-proper-motion K dwarf HIP 116454

2 DATA AND ANALYSIS

21 K2 Photometry

HIP 116454 and nearly 2000 other stars were observed by theKepler spacecraft from 2014 February 4 until 2014 February 12during the Kepler Two-Wheel Concept Engineering Test Afterthe first 25 days of the test Kepler underwent a large intentionaladjustment to its pointing to move its target stars to the centerof their apertures where they stayed for the last 65 days of thetest We downloaded the full engineering test data set from theMikulski Archive for Space Telescopes (MAST) and reducedthe Kepler target pixel files as described in VJ14

In brief we extracted raw aperture photometry and imagecentroid positions from the Kepler target pixel files Raw K2photometry is dominated by jagged events corresponding to themotion of the spacecraft as Keplerrsquos pointing drifts becauseof solar radiation pressure and is periodically corrected withthrusters For the last 65 days after the large pointing tweak we

Table 1Astrometric and Photometric Properties of HIP 116454

Parameter Value Uncertainty Source

α (J2000) 23 35 4928 Hipparcos a

δ (J2000) +00 26 4386 Hipparcosμα (mas yrminus1) minus2380 17 Hipparcosμδ (mas yrminus1) minus1859 09 Hipparcosπ (mas) 181 172 HipparcosB 1108 001 TychoV 10190 0009 Tycho b

R 971 003 TASSc

I 925 003 TASSu 14786 002 SDSSd

g 10837 002 SDSSr 9908 002 SDSSi 9680 002 SDSSJ 860 002 2MASSe

H 814 003 2MASSKS 803 002 2MASS

Notesa van Leeuwen (2007)b Egret et al (1994)c Richmond et al (2000)d Abazajian et al (2009)e Skrutskie et al (2006)

removed the systematics due to the motion of the spacecraft bycorrelating the measured flux with the image centroid positionsmeasured from photometry We essentially produced a ldquoselfflat fieldrdquo (SFF) similar to those produced by for instanceBallard et al (2010) for analysis of Spitzer photometry We fita piecewise linear function to the measured dependence of fluxon centroid position with outlier exclusion to preserve transitevents and removed the dependence on centroid position fromthe raw light curve Similar to VJ14 we excluded data pointstaken while Keplerrsquos thrusters were firing from our reducedlight curves because these data were typically outliers from thecorrected light curves For HIP 116454 the median absolutedeviation (MAD) of the 30-minute-long cadence data pointsimproved from 500 parts per million (ppm) for the raw lightcurve to 50 ppm for the SFF light curve

Visual inspection of light curves from the 2000 targetsobserved during the engineering test revealed a 1 millimagnitude(mmag) deep candidate transit in photometry of HIP 116454designated EPIC 60021410 by the Kepler team HIP 116454rsquosphotometric and astrometric measurements are summarized inTable 1 Raw and corrected K2 photometry for HIP 116454are shown in Figure 1 We fit a Mandel amp Agol (2002) modelto the transit and measured a total duration of approximately225 hr and a planet-to-star radius ratio of approximately 003Unfortunately the data point during transit ingress happenedduring a thruster firing event and was excluded by our pipelineThis particular data point does not appear to be anomalous butwe choose to exclude it to minimize risk of contaminating thetransit with an outlier Slow photometric variability presumablydue to starspot modulation is evident in the K2 light curve atthe subpercent level

We also performed a similar SFF correction to the data takenin the 25 days of data before the large pointing tweak Eventhough the resulting data quality is somewhat worse we are ableto confidently exclude any other events of a similar depth duringthat time

Because K2 only observed one transit event we were notable to measure a precise orbital period for the planet candidate

2


1862 1864 1866 1868 1870BJD - 2454833

0998

1000

1002

1004

1006

Rel

ativ

e B

right

ness

Raw 6 hour precision 1937 ppm

Corrected 6 hour precision 245 ppm

Figure 1 Raw (top blue) and SFF-corrected (bottom orange) K2 light curves K2 only observed HIP 116454 for 9 days in 2014 February the last 65 of which areshown here The raw data is vertically offset for clarity A transit model light curve multiplied by a basis spline fit to the out-of-transit variations is overplotted on thecorrected K2 data The 6 hr photometric precision on this target (as defined by VJ14) improves by a factor of seven as a result of the SFF processing

Nonetheless we were able to put rough constraints on the orbitalperiod from our knowledge of the transit duration and estimatesof the stellar properties The 9 day time baseline of the K2observations allowed us to constrain the period of the candidatetransiting planet to be greater than 5 days To put a roughupper bound on the allowed planet period we compared thetransit duration of the candidate transit around HIP 116454to the distribution of transit durations from the ensemble ofKepler planet candidates (retrieved from the NASA ExoplanetArchive Akeson et al 2013) We found that of the 413 Keplerplanet candidates with transit durations between 2 and 25 hr93 had orbital periods shorter than 20 days Because transitduration is a function of the mean stellar density we repeatedthis calculation while restricting the sample to the 64 planetcandidates with transit durations between 2 and 25 hr and host-star effective temperatures within 200 K of HIP 116454 Wefind similarly that 94 of these candidates had orbital periodsshorter than 20 days

22 Imaging

221 Archival Imaging

We used a combination of modern and archival imag-ing to limit potential false-positive scenarios for the transitevent HIP 116454 was observed in the National GeographicSocietyndashPalomar Observatory Sky Survey (POSS-I) on 1951November 28 HIP 116454 has a proper motion of 303 mas yrminus1

(van Leeuwen 2007) and therefore has moved nearly20 arcsec with respect to background sources since being im-aged in POSS-I Inspection of the POSS-I image reveals nobackground objects within the K2 aperture used in our photo-metric reduction We show the POSS-I blue image overlaid withthe K2 photometric aperture in Figure 2(a) The POSS-I surveyhas a limiting magnitude of 211 in the blue bandpass (Abell1955) 10 mag fainter than HIP 116454 The depth of the de-tected transit is 01 so if a background eclipsing binary wereresponsible the depth would correspond to a total eclipse of astar 75 mag fainter A low-proper-motion background star suchas that would have readily been detected in POSS-I imaging We

conclude that our aperture is free of background objects whoseeclipses could masquerade as planet transits

The POSS-I imaging also reveals a companion star about 8arcsec to the southwest of HIP 116454 The companion is notfully resolved in POSS-I because the photographic plate wassaturated by the bright primary star but an asymmetry in thestellar image is visible HIP 116454 was also observed dur-ing the Second Palomar Observatory Sky Survey (POSS-II)on 1992 August 31 Improvements in photographic plate tech-nology over the previous 40 yr allowed the companion star tobe resolved The companion shares a common proper motionwith the primary at a projected distance of 500 AU so weconclude that the two stars are a gravitationally bound visualbinary system

222 Modern Imaging

HIP 116454 was observed during the Sloan Digital SkySurvey (SDSS) and the secondary star was detected (Abazajianet al 2009) The secondary star falls on a diffraction spikecaused by the much brighter primary star but the SDSS pipelineflagged its photometry as ldquoacceptablerdquo The SDSS photometryindicates that the secondary star is 6ndash7 mag fainter than theprimary depending on the filter so because the two stars aregravitationally associated the secondary must be intrinsicallymuch fainter than the K-dwarf primary This implies that thecompanion must either be a late M dwarf or a white dwarfThe SDSS colors are relatively flat indicating a hot star Toquantify this we fit the ugri SDSS colors to a blackbodymodel excluding z because of its low throughput and assumingphotometric errors of 5 We included no corrections forextinction because of the proximity of the target and our abilityto accurately predict broadband photometry using stellar modelsin Section 312 We find that the data are best described by anobject radiating at a temperature of TWD = 7500 plusmn 200 K Weused the StefanndashBoltzmann law combined with the Hipparcosparallax and derived the temperature to estimate a radius ofRWD = 12 plusmn 01 Roplus which is consistent with our white dwarfhypothesis Using a simple analytic white dwarf cooling law(Mestel 1952 Gansicke 1997) we estimate a cooling age of

3


Figure 2 Imaging of HIP 116454 Archival image from the POSS-I survey taken in 1951 showing a clear background in the K2 aperture (shown in red) (b) Archivalimage from the POSS-II survey taken in 1992 showing the high proper motion of the star (c) Coadded image of the last 5 days of the K2 engineering test (d) Zoomedand scaled version of the POSS-I image showing the companion (e) Modern KeckNIRC2 image of the HIP 116454 system showing that the companion sharesproper motion with HIP 116454 In this image the primary was intentionally saturated to simultaneously image the companion (f) Robo-AO adaptive optics imagein an optical bandpass close to that of Kepler showing no apparent close companions NIRC2 images also exclude companions at even closer angular separations butin infrared bandpasses

the white dwarf of tcool sim 13 Gyr The formal uncertainty onthe cooling age is 02 Gyr but this neglects uncertainties thatare due to the unknown composition of the white dwarf andinaccuracies in the simple model The true uncertainty on thisquantity is likely on the order of a factor of two (van Horn 1971)The cooling age of the white dwarf is a lower limit on the ageof the system and the total age of the system is the sum of themain sequence lifetime of the progenitor and the white dwarfrsquoscooling age

The secondary star is close enough to the primary that it isblended in the K2 image and is bright enough that if it werea totally eclipsing binary it could cause the transit event weobserved This situation is unlikely because the duration andminimum period of the event are generally inconsistent with anobject eclipsing a white dwarf With the baseline of K2 data wecan exclude orbital periods shorter than 5 days While 5-day-period companions eclipsing main-sequence stars are commonand have relatively high transit probabilities the probability ofa transit or eclipse goes as P prop R at a given stellar massand orbital period Furthermore in order for an Earth-sizedobject eclipsing a white dwarf to have an eclipse duration of2 hr the orbital period would have to be roughly 600 yr inthe case of a circular orbit and impact parameter b = 0 Evenwith a highly elliptical orbit transiting at apastron which isa priori unlikely the orbital period would be on the order of

centuries and the semimajor axis would be roughly 50 AU Theprobability of an orbit such as that eclipsing the white dwarf isP sim (R +Rp)a sim 10minus6 where a is the semimajor axis and Rpis the radius of the occulting body In the worst-case scenario ofa non-luminous Jupiter-sized object occulting the white dwarfthe orbital period would have to be on the order of 3 yr and havea semimajor axis of roughly 15 AU corresponding to a transitprobability of P sim 10minus4 We conclude that the transit event weobserved was far more likely caused by a short-period planetorbiting the primary star than a long-period object eclipsing thesecondary

223 Adaptive Optics Imaging

We also obtained high-angular-resolution imaging of theprimary star to rule out any very close associated companionsWe observed HIP 116454 with the Robo-AO laser adaptiveoptics and imaging system on the 60 inch telescope at PalomarObservatory (Baranec et al 2014 Law et al 2014) We obtainedseven images with Robo-AO between 2014 June 15 and 2014July 11 in three different bandpasses Sloan i band Sloan z bandand a long-pass filter with a cutoff at 600 nm (LP600) that moreclosely approximates the Kepler bandpass Each observationconsisted of a series of images read out from the detector at amaximum rate of 86 Hz for a total integration time of 90 s

4


The frames were coadded in postprocessing using a shift-and-add technique with HIP 116454 as the tipndashtilt guide star

The quality of the Robo-AO images varied between theobservations but none of the images showed evidence forcompanions within three magnitudes of the primary outsideof 02 arcsec Some but not all of the images however showedan elongation that could be consistent with a bright close binarycompanion at a separation of 015 arcsec at the lt5-σ levelsimilar to KOI 1962 in Law et al (2014)

To investigate this possibility further we obtained higher res-olution adaptive-optics images on 2014 August 2 using theKeck II Natural Guide Star Adaptive Optics (NGSAO) sys-tem with the NIRC2 narrow detector at Keck ObservatoryWe obtained unsaturated frames of HIP 116454 in J- H- andKS-band filters to search for close companions near the diffrac-tion limit (sim40 mas in the H band) We also acquired deepersaturated images in the H (70 s total) and KS bands (200 s total)with the primary positioned in the lower-right quadrant of thearray and rotated so the white dwarf companion falls in the fieldof view We calibrated and processed the data as described inBowler et al (2012) We corrected the data for optical aber-rations using the distortion solution from B Cameron (2007private communication) and north-aligned the images using thedetector orientation measured by Yelda et al (2010) We foundno evidence for the companion suggested by some of the Robo-AO data Our 7σ H-band limiting contrasts are 30 59 6892 108 127 mag at separations of 0primeprime1 0primeprime3 0primeprime5 1primeprime0 2primeprime05primeprime0 We are able to exclude roughly equal brightness compan-ions to an angular separation of 004 arcsec (projected distanceof 22 AU)

23 Reconnaissance Spectroscopy

HIP 116454 was observed nine times for the CarneyndashLathamProper Motion Survey (Latham et al 2002) with the CfADigital Speedometer spectrograph over the course of 91 yrfrom 1982 until 1991 The Digital Speedometer measuredradial velocities to a precision of approximately 03 km sminus1anddetected no significant RV variations or trends in the velocitiesof HIP 116454 When corrected into an absolute RV framethe Digital Speedometer measurements indicate an absoluteRV of minus306 plusmn 012 km sminus1 and when combined with propermotion a space velocity of (UVW ) = (minus867minus02 45) plusmn(76 12 05) km sminus1 This somewhat unusual space velocitycorresponds to an elliptical orbit in the plane of the galaxyindicating that HIP 116454 originated far from the stellarneighborhood A detailed analysis of HIP 116454rsquos elementalabundances could reveal patterns that are dissimilar to stars inthe solar neighborhood

We obtained three observations of HIP 116454 in June of 2014with the Tillinghast Reflector Echelle Spectrograph (TRES)on the 15 m Tillinghast Reflector at the Fred L WhippleObservatory The spectra were taken with a resolving power ofR = 44 000 with a signal-to-noise ratio (SN) of approximately50 per resolution element When corrected into an absolute RVframe the TRES spectra indicate an absolute RV for HIP 116454of minus312plusmn01 km sminus1 When combined with the absolute radialvelocities from the Digital Speedometer there is no evidence fora RV variation of greater than 100 m sminus1 over the course of 30 yrThe three individual radial velocities from the TRES spectrarevealed no variability at the level of 20 m sminus1 over the courseof 8 days We also find no evidence for a second set of stellarlines in the cross-correlation function used to measure the radialvelocities which rules out many possible close companions

Table 2HARPS-N Radial Velocities of HIP 116454

BJD - 2454833 RV σRV

(m sminus1) (m sminus1)

20127150 minus651 11320137062 minus315 13720147001 minus444 23520156955 minus262 11220166307 101 18820177029 431 12420186971 103 11020196985 033 18320207000 minus317 13120256645 minus057 12220266780 minus005 13920276258 233 10020286266 minus057 10820307261 minus048 11920317186 minus369 09020327231 minus282 10520337197 minus153 18720416353 minus132 12820436442 minus172 23020446658 728 13220457016 502 12120507205 minus516 14120517258 minus364 09720527229 minus140 11120537166 253 16020547304 429 09220556129 102 13420565885 020 14320576126 minus309 08720865397 minus197 10720905445 601 07620915401 458 09720985448 210 148

or background stars When the adaptive optics constraints arecombined with a lack of RV variability of more than 100 m sminus1

over 30 yr and the lack of a second set of spectral lines in thecross-correlation function we can effectively exclude any closestellar companions to HIP 116454

24 HARPS-N Spectroscopy

We obtained 44 spectra of HIP 116454 on 33 differentnights between July and October of 2014 with the HARPS-Nspectrograph (Cosentino et al 2012) on the 357 m TelescopioNazionale Galileo (TNG) on La Palma Island Spain to measureprecise radial velocities and determine the orbit and mass ofthe transiting planet Each HARPS-N spectrum was taken witha resolving power of R = 115000 and each measurementconsisted of a 15 minute exposure yielding an SN of 50ndash100per resolution element at 550 nm depending on weatherconditions The corresponding (formal) RV precision rangedfrom 090 m sminus1 to 235 m sminus1 Radial velocities were extractedby calculating the weighted cross-correlation function of thespectrum with a binary mask (Baranne et al 1996 Pepe et al2002) In some cases we took one 15 minute exposure per nightand in other cases we took two 15 minute exposures back-to-back In the latter case we measured the two consecutive radialvelocities individually and report the average value

The HARPS-N RV measurements are listed in Table 2 Aperiodic RV variation with a period of about 9 days and asemiamplitude of about 4 m sminus1 is evident in the RV time

5


1 10 100Period [day]

0

5

10

15Lo

mb-

Sca

rgle

Pow

er

P = 00001

Figure 3 Left LombndashScargle periodogram of the HARPS-N radial velocitydata We find a strong peak at a period of 91 days and see daily aliases of the91 day signal with periods close to 1 day The horizontal blue line indicates afalse alarm probability of 00001 and the vertical red hash mark indicates theperiod (912 days) from our combined analysis described in Section 32

series We checked that we identified the correct periodicityby calculating a LombndashScargle periodogram (Scargle 1982)shown in Figure 3 We found a strong peak at a period of 91 daysand an aliased peak of similar strength with a period close to1 day corresponding to the daily sampling alias of the 91 daysignal (eg Dawson amp Fabrycky 2010) We estimated the falsealarm probability of the RV detection by scrambling the RV dataand recalculating the periodogram numerous times and countingwhich fraction of the scrambled periodograms have periods withhigher power than the unscrambled periodogram We foundthat the false alarm probability of the 91 day periodicity issignificantly less than 10minus4

In addition to the 91 day signal we also found evidencefor a weaker 45 day periodic RV variation To help decidewhether to include the second periodicity in our RV modelingwe fit the HARPS-N radial velocities with both a one-planetand a two-planet Keplerian model The one-planet model wasa Keplerian function parameterized by log(P ) time of transitlog (RVsemiamplitude)

radice sin(ω) and

radice cos(ω) where P is

the planetrsquos orbital period e is the orbital eccentricity and ω isthe argument of periastron We also fit for a RV zero point and astellar jitter term for a total of seven free parameters We fit eachof these parameters with an unbounded uniform prior exceptfor

radice sin(ω) and

radice cos(ω) which had uniform priors over the

interval between minus1 and 1 The two-planet model was the sumof two Keplerian functions each of which was parameterizedby log(P ) time of transit log (RVsemiamplitude)

radice sin(ω)

andradic

e cos(ω) Once again we also fit for a RV zero point andstellar jitter term for a total of 12 free parameters We fit eachof these parameters with an unbounded uniform prior except forradic

e sin(ω) andradic

e cos(ω) which had uniform priors over theinterval between -1 and 1 and for log P2 the period of the outerplanet which we constrained to be between the period of theinner planet and 1000 days We performed the fits using emcee(Foreman-Mackey et al 2013) a Markov chain Monte Carlo(MCMC) algorithm with an affine invariant ensemble samplerWe note that upon exploring various different periods for theouter planet our MCMC analysis found the 45 day period tobe optimal We calculated the Bayesian information criterion(BIC Schwarz 1978) to estimate the relative likelihoods of thetwo models Although the BIC does not provide a definitive orexact comparison of the fully marginalized likelihoods of themodels it allows us to roughly estimate the relative likelihoodsUpon calculating the BIC we estimate that the two-planet modelis favored over the one-planet model with confidence P sim 003From here on we therefore model the RV observations asthe sum of two Keplerian functions We show our HARPS-Nmeasurements and our best-fitting model in Figure 4

For both periods we find an amplitude consistent with thatof a transiting super-Earth The 9 day periodicity in the RVsis consistent with the orbital period we estimated from theduration of the K2 transit event We ldquopredictedrdquo the time oftransit for the 9 day period planet during the K2 observationsand found that the HARPS-N measurements alone constrain theexpected time of transit to better than 1 day and we find that theK2 transit event is consistent with the transit ephemeris predictedby only the HARPS-N RVs at the 683 (1σ ) level We show

2020 2040 2060 2080 2100BJD minus 2454833 [days]

minus10

minus5

0

5

10

Rad

ial V

eloc

ity [m

sminus1 ]

RMS = 126 msminus1

91 Day Period

00 02 04 06 08 10Orbital Phase

minus10

minus5

0

5

10

RV

[msminus

1 ]

45 Day Period


minus6minus4minus2

0246

RV

[msminus

1 ]

Figure 4 Top all radial velocity measurements of HIP 116454 with observations taken during the same night binned together We strongly detect a 91 day periodicityand find more tenuous evidence for a 45 day periodicity Bottom left RV measurements phase folded on the 91 day period with the best-fit 45 day signal removedBottom right RV measurements phase folded on the 45 day period with the best-fit 91 day signal removed

6


1862 1864 1866 1868BJD - 2454833 [days]

09985

09990

09995

10000

10005

10010

Rel

ativ

e B

right

ness

1-σ TransitWindowfrom RVs


























1862 1864 1866 1868BJD - 2454833 [days]

09985

09990

09995

10000

10005

10010

Rel

ativ

e B

right

ness

Figure 5 K2 light curve (orange dots) overlaid with the transit window derived from the HARPS-N radial velocities (blue shaded region) We show the full K2 lightcurve including data taken before Keplerrsquos large pointing tweak at t 18624 days (data to the left of the dashed line) The green shaded region near t 18616 daysis half a phase away from the transit assuming a 912 day period No secondary eclipse is visible lending credence to the planetary interpretation of the transit andRV variations

the K2 light curve with the transit window derived from onlythe HARPS-N RVs in Figure 5 Thus the 91 day periodicity isconsistent with being caused by a transiting planet The moretenuous 45 day periodic variation on the other hand may be dueto an outer planet but it may also be caused by stellar variability

The HARPS-N spectra include regions used to calculateactivity indicators such as the Mount Wilson SHK index and theRprime

HK index (eg Wright et al 2004) We calculated the SHK indexfor each HARPS-N spectrum and found a mean value of 0275 plusmn00034 and an associated log10 Rprime

HK = minus4773 plusmn 0007 Therewere no obvious correlations between the SHK index and eitherthe measured RV or the residuals to either a one- or two-planetKeplerian fit

25 Photometry

251 WASP

HIP 116454 was observed by the SuperWASP-N instrumenton La Palma Spain and the SuperWASP-S instrument at theSouth African Astronomical Observatory (Pollacco et al 2006)The observations spanned three observing seasons from 2008 to2010 and consisted of roughly 15000 data points with a typicalprecision of 06 The WASP observations are consistent witha typical level of stellar variability at the subpercent level TheWASP data rule out deep transits but are not of high enoughquality to detect the 01 transit depth observed by K2 InSection 313 we use the WASP light curve in combinationwith light curves from K2 and MOST to attempt to deriveHIP 116454rsquos rotation period

252 MOST

After detecting the K2 transit we obtained follow-up photo-metric observations with the MOST (Walker et al 2003) spacetelescope during August and September of 2014 MOST ob-served HIP 116454 during three nearly continuous time spans13 days from 2014 August 3 to 2014 August 16 18 days from2014 August 21 to 2014 September 9 and 35 days from 2014September 15 to 2014 September 18 During the first segment ofthe MOST data observations of HIP 116454 were interleavedwith observations of other stars during the satellitersquos orbit aroundEarth but for the second and third segments MOST observed

HIP 116454 continuously During the first and third segmentsthe exposure time for individual data points was 1 s and duringthe second segment the exposure time was 2 s

We processed the MOST data using aperture photometrytechniques as described in Rowe et al (2006) Backgroundscattered light (modulated by the 101 minute orbital periodof MOST) and interpixel sensitivity variations were removedby subtracting polynomial fits to the correlations between thestellar flux the estimated background flux and the centroidcoordinates of the star At each stage outlying data points wereexcluded by either sigma clipping or hard cuts The resultingprecision of the MOST light curve was approximately 02 per2 s exposure

When we search the MOST light curve at the predicted timesof transits from a simultaneous analysis of the K2 and HARPS-Ndata we detect a weak signal with the same depth durationand ephemeris as the K2 transit The MOST light curve isshown in Figure 6 The MOST data refine our estimate of thetransiting planet period to a precision of roughly 30 s We takethis detection as confirmation that the 91 day period detected inradial velocities is in fact caused by the transiting planet Fromhere on we refer to the 91 day period planet as HIP 116454 b

3 ANALYSIS AND RESULTS

31 Stellar Properties

311 Spectroscopic Parameters of the Primary

We measured the spectroscopic properties of the hoststar using the stellar parameter classification (SPC) method(Buchhave et al 2012) on the spectra from TRES andHARPS-N An analysis of spectra from both instrumentsshowed consistent results for the stellar parameters We adoptthe results from the HARPS-N spectra because of their higherspectral resolution and SN The SPC analysis yields an ef-fective temperature of 5089 plusmn 50 K a metallicity of [MH]= minus016 plusmn 008 and a surface gravity of log g = 455 plusmn 01We did not detect significant rotational broadening even withthe high-resolution HARPS-N spectra The upper limit on theprojected rotational velocity is roughly v sin(i) 2 km sminus1

7


-4 -2 0 2 4Hours from Midtransit

0996

0998

1000

1002

1004

Rel

ativ

e B

right

ness

K2

MOST

Figure 6 K2 light curve (red dots) and binned MOST light curves (blue dots)Best-fit models are overplotted in solid black lines Individual MOST data pointsare shown as gray dots The K2 light curve is vertically offset for clarity TheMOST data yield a marginal (3-σ ) detection of the transit at the time predictedby HARPS-N radial velocities and the K2 light curve

312 Stellar Mass and Radius

We used several different approaches to estimate the stellarmass and radius of HIP 116454 First we used the SPC param-eters in particular the metallicity surface gravity and effectivetemperature to interpolate onto the YonseindashYale stellar evolu-tion model grids (Yi et al 2001) using a Monte Carlo approachThe resulting stellar parameters were M = 0772 plusmn 0033 Mand R = 0746 plusmn 0042R

HIP 116454 was observed by Hipparcos and has a mea-sured parallax allowing us to interpolate model grids usinga separate luminosity indicator We used the online Padovamodel interpolator31 which uses the technique of da Silvaet al (2006) to interpolate a measured effective temperaturemetallicity V-band magnitude and parallax onto PARSECisochrones yielding estimates of stellar mass radius surfacegravity and BminusV color When the SPC parameters Hippar-cos parallax and the V magnitude from the Tycho catalog(Egret et al 1994) are provided as input the models outputM = 0775 plusmn 0027M and R = 0716 plusmn 0024 Ralong with log g = 4590 plusmn 0026 dex and BminusV = 0935 plusmn0018 mag

The model-predicted surface gravity is consistent with thespectroscopically measured surface gravity and is more precisebecause of the additional constraint from parallax The modeloutput BminusV color is discrepant with the measured Tycho BminusVat the 15σ level but it is still within 004 mag of the measuredTycho BminusV = 09 This discrepancy is small enough (3) that

31 httpstevoapdinafitcgi-binparam

it could be due to differences in the filters used by Tycho andthe filter transmission assumed by the Padova models

We adopt the outputs from the Padova model interpolator asour stellar parameters because of their more precise constraintsand ability to predict log g and BminusV

313 Stellar Rotation Period

We attempted to measure the rotation period of HIP 116454using photometric measurements from WASP MOST andK2 to see if stellar activity might contribute to the possible45 day periodicity in the RV measurements A constraintor measurement of the rotation period consistent with thepossible 45 day periodicity in radial velocities could affectour interpretation of the signal We only used photometricmeasurements for our analysis given the relatively short timecoverage and sparseness of the spectroscopic observations

We first started by analyzing the WASP data only becauseits time baseline far exceeded that of the K2 and MOSTdata We binned the WASP data into nightly data pointscalculated a LombndashScargle periodogram and Fourier trans-formed the resulting power spectrum to obtain an autocor-relation function The resulting periodograms and autocorre-lation functions are shown in Figure 7 We performed thisanalysis on each season of WASP data individually In the firstseason (2008) of WASP data we found a moderately strongpeak in both the autocorrelation function and the LombndashScargleperiodogram at a period of about 16 days We evaluated thesignificance of this peak by scrambling the binned data re-calculating the LombndashScargle periodograms and counting thenumber of times the maximum resulting power was greater thanthe power in the 16 day peak We found a false alarm proba-bility of 2 for the peak in the first season We did not findany convincing signals in the second (2009) or third (2010) ob-serving seasons A possible explanation for the inconsistencybetween observing seasons is that HIP 116454 experienced dif-ferent levels of starspot activity but it is also possible that the16 day period detected in the first season is spurious We con-cluded that the WASP data showed a candidate rotation period at16 days but the relatively high false alarm probability and lackof consistency between observing seasons precluded a confidentdetection

After our analysis of the WASP data yielded suggestiveyet ambiguous results we attempted to measure the rotationperiod of HIP 116454 by fitting all of the photometric datawith a Gaussian process noise model Stochastic yet time-correlated processes such as the variability produced by rotationin stellar light curves can be modeled as a Gaussian processby parameterizing the covariance matrix describing the timecorrelation between data points with a kernel function andinferring kernel hyperparameters from the data We use a quasi-periodic kernel function for the specific problem of measuringa rotation period from a light curve This in principle isbetter suited to inferring the rotation period of a star thana periodogram analysis because the variability produced byactive surface regions on a rotating star is typically neithersinusoidal nor strictly periodic The Gaussian process analysisalso allows us to simultaneously model multiple data sets and totake advantage of data sets (like K2 and MOST) with relativelyshort time coverage

We conducted our analysis using george (Foreman-Mackeyet al 2014) a Gaussian process library that employsHierarchical Off-Diagonal Low Rank Systems (HODLR) a fastmatrix inversion method (Ambikasaran et al 2014) We used

8


Season 1 Lomb-Scargle Periodogram

10 20 30 40 50Period [days]

02

4

6

8

10

12

L-S

Pow

er

P = 001

Season 1 Autocorrelation Function

0 10 20 30 40 50Lag [days]

000

005

010

015

020

Am

plitu

de


10 20 30 40 50Period [days]

02

4

6

8

10

12

L-S

Pow

er

P = 001


0 10 20 30 40 50Lag [days]

000

005

010

015

020

Am

plitu

de


10 20 30 40 50Period [days]

02

4

6

8

10

12

L-S

Pow

er

P = 001


0 10 20 30 40 50Lag [days]

000

005

010

015

020

Am

plitu

de

Figure 7 LombndashScargle periodograms and autocorrelation functions for three observing seasons of WASP data The first observing season (2008) shows evidencefor a roughly 16 day rotation period in both the periodogram and autocorrelation function We mark a 163 day period in each figure with a red hash mark and showthe level of a 1 false alarm probability with a horizontal blue line

the following kernel function in our analysis

kij = A2 exp

[minus(xi minus xj )2

2l2

]exp

⎡⎣minus sin2

(π (ximinusxj )

P

)g2

q

⎤⎦ (1)

where A is the amplitude of correlation l is the timescale ofexponential decay gq is a scaling factor for the exponentiatedsinusoidal term and P is the rotation period An additionalhyperparameter s was used to account for additional whitenoise in the time series where s is added to the individualmeasurement uncertainties in quadrature

We modeled the three continuous periods of MOST datathe three seasons of WASP data and the K2 photometrysimultaneously with A l gq and P constrained to be thesame across all seven data sets and with s allowed to take adifferent value for each We used emcee to explore the posteriordistributions of the hyperparameters The resulting posteriordistribution was not well constrained with significant power atessentially all rotation periods greater than about 8 days and lessthan about 50 days There were a few periods that seemed to bepreferred to some extent in the posterior distribution a strongpeak at 12 days and weaker peaks at 16 20 and 32 days

We conclude that with our data we cannot conclusivelyidentify a rotation period for HIP 116454 which leaves usunable to rule out stellar activity as the cause of the 45 daysignal in the radial velocities While we do not find any strongevidence in the photometry that the rotation period is closeto 45 days we cannot conclusively rule out a 45 day rotation

period More photometric (or spectroscopic) observations willbe important to determining HIP 116454rsquos rotation period

32 Joint Analysis and Planet Properties

We conducted an analysis of the K2 light curve the HARPS-NRV observations the MOST light curve and the WASP lightcurve to determine orbital and planetary properties We firstreprocessed the K2 data using a different method from thatdescribed in VJ14 to minimize the possibility of any bias dueto using the in-transit points in the flat field We rederived theSFF correction by fitting the K2 light curve using an MCMCalgorithm with an affine invariant ensemble sampler (adapted forIDL from the algorithm of Goodman amp Weare 2010 Foreman-Mackey et al 2013) We fit the transit light curve with a Mandelamp Agol (2002) model as implemented by Eastman et al (2013)with quadratic limb-darkening coefficients held at the valuesgiven by Claret amp Bloemen (2011) We modeled the stellarout-of-transit variations with a cubic spline between 10 nodesspaced evenly in time the heights of which were free parametersSimilarly we modeled the SFF correction as a cubic spline with15 nodes spaced evenly in ldquoarclengthrdquo a one-dimensional metricof position on the detector as defined in VJ14 Upon findingthe best-fit parameters for the SFF correction we applied thecorrection to the raw K2 data to obtain a debiased light curve

After rederiving the correction to the K2 light curve wesimultaneously fit a transit light curve to the K2 light curvethe HARPS-N radial velocities and the MOST and WASPphotometry using emcee We modeled the RV variations with

9


Table 3System Parameters for HIP 116454

Parameter Value 683 Confidence CommentInterval Width

Orbital parameters

Orbital period P (days) 91205 plusmn 00005 ARadius ratio (RP R) 00311 plusmn 00017 ATransit depth (RP R)2 0000967 plusmn 0000109 AScaled semimajor axis aR 2722 plusmn 114 AOrbital inclination i (deg) 8843 plusmn 040 ATransit impact parameter b 065 plusmn 017 AEccentricity 0205 plusmn 0072 AArgument of Periastron ω (deg) minus591 plusmn 167 AVelocity semiamplitude K (m sminus1) 441 plusmn 050 ATime of Transit tt (BJD) 245690789 plusmn 003 A

Stellar parameters

M (M) 0775 plusmn 0027 B DR (R) 0716 plusmn 0024 B Dρ (ρ) 211 plusmn 023 B Dlog g (cgs) 4590 plusmn 0026 B[MH] minus016 plusmn 008 BDistance (pc) 552 plusmn 54 DTeff (K) 5089 plusmn 50 B

Planet parameters

MP (Moplus) 1182 plusmn 133 B C DRP (Roplus) 253 plusmn 018 B C DMean planet density ρp (g cmminus3) 417 plusmn 108 B C Dlog gp (cgs) 326 plusmn 008 B C DEquilibrium temperature Teff (

R2a

)12 (K) 690 plusmn 14 B C D E

Notes (A) Determined from our analysis of the K2 light curve the HARPS-N radial velocity measurements the MOST light curve andthe stellar parameters (B) Based on our spectroscopic analysis of the HARPS-N spectra (C) Based on group A parameters (D) Basedon the Hipparcos parallax (E) Assuming albedo of zero and perfect heat redistribution

a two-planet Keplerian model (fitting the 91 day period andthe 45 day period simultaneously) and modeled the transitsof the 91 day planet with a Mandel amp Agol (2002) modelFor the K2 light curve we accounted for the 294-minute-long cadence exposure time by oversampling the model lightcurve by a factor of 13 and binning We allowed limb-darkeningcoefficients (parameterized as suggested by Kipping 2013) tofloat We used a white-noise model for the RV observationswith a stellar jitter term added in quadrature to the HARPS-N formal measurement uncertainties For the light curves weused a Gaussian process noise model using the same kerneldescribed in Equation (1) We used an informative prior on thestellar log g from Section 312 in our fits which we convertedto stellar density to help break the degeneracy between the scaledsemimajor axis and the impact parameter Using this prior letus constrain the impact parameter despite having only one K2long-cadence data point during transit ingress and egress Intotal the model had 28 free parameters We used emcee tosample the likelihood space with 500 ldquowalkersrdquo each of whichwe evolved through 1500 steps We recorded the last 300 of thesesteps as samples of our posterior distribution giving a total of150000 MCMC links We calculated correlation lengths for all28 parameters which ranged from 56 to 190 corresponding tobetween 8000 and 27000 independent samples per parameterWe assessed the convergence of the MCMC chains using thespectral density diagnostic test of Geweke (1992) and foundthat the means of the two sequences are consistent for 2128parameters (75) at the 1σ level for 2728 (96) at the 2σlevel and 2828 at the 3σ level These fractions are consistent

with draws from a normal distribution which is the expectedbehavior for the MCMC chains having converged

In Table 3 we report the best-fitting planet and orbit parame-ters and their uncertainties for HIP 116454 b by calculating themedian link for each parameter and 68 confidence intervalsof all links for each parameter respectively We summarize thepriors used in the fits and the full model outputs in Table 4including nuisance parameters like the noise model outputs Wealso make our posterior samples available for download as aFITS file

We find that our data are best described by the presence of aplanet with Rp = 253 plusmn 018 Moplus and Mp = 1182 plusmn 133 Moplusina 91205 day orbit While we find some evidence for an outerplanet in the RV measurements we cannot conclusively claimits existence based on the data presently at our disposal

4 DISCUSSION

41 Composition of HIP 116454 b

Figure 8 shows HIP 116454 b on a massndashradius diagramwith other known transiting sub-Neptune-sized exoplanets withmeasured masses and radii We overlaid the plot with modelcomposition contours from Zeng amp Sasselov (2013) We firstnote that HIP 116454 b has a mass and radius consistent witheither a low-density solid planet or a planet with a dense core andan extended gaseous envelope The relatively low equilibriumtemperature of the planet (Teq = 690 plusmn 14 K assuming zeroalbedo and perfect heat redistribution) makes it unlikely that any

10


Figure 8 Left massndashradius diagram for sub-Neptune-sized exoplanets HIP 116454 b is consistent with being entirely solid but it has a density low enough thatit could also have a substantial gaseous envelope surrounding a dense core It is similar in mass radius and density to HD 97658b and Kepler 68b Right ternarydiagram showing allowed compositions for solid exoplanets Assuming HIP 116454 b is solid the thick dashed line represents allowed compositions for a planet withour best-fitting mass and radius and the dashed line indicates the compositions allowed within 1σ uncertainties To 1σ the planet must have at least 30 water orother volatiles

Table 4Summary of Combined Analysis

Parameter Prior 50 Value 158 842radic

e1 cos(ω1) U(minus1 1) 0244 minus0052 +0049radice1 sin(ω1) U(minus1 1) minus0395 minus0091 +0109

tt1 [BJD] U(minusinfininfin) 2456907895 minus0037 +0015log (P1 dayminus1) U(minusinfininfin) 2210472 minus0000176 +0000079log (M1MJup) U(minusinfininfin) minus3286 minus0111 +0089cos i1 U(minus1 1) minus00296 minus00038 +00023radic


tt2 [BJD] U(minusinfininfin) 24569308 minus54 +57log (P2 dayminus1) U(minusinfininfin) 3838 minus0082 +0093log (M2 sin i2MJup) U(minusinfininfin) minus222 minus029 +028log Rp1R U(minusinfininfin) minus3443 minus0039 +0042q1 U(0 1) 037 minus024 +033q2 U(0 1 minus q1) 041 minus039 +029RV zero point (m sminus1) U(minusinfininfin) minus042 minus034 +033Jitter (m sminus1) U(minusinfininfin) 045 minus028 +032log g N (459 0026) 4591 minus0020 +0022log A U(minus20 55) minus1305 minus033 +035log l U(minus2 85) 133 minus093 +133log gq U(minus8 7) 27 minus16 +14log (Prot dayminus1) U(2 4) 331 minus078 +053log σWASP1 U(minus675minus175) minus41 minus18 +18log σWASP2 U(minus675minus175) minus42 minus18 +18log σWASP3 U(minus675minus175) minus43 minus17 +19log σK2 U(minus11 minus6) minus9284 minus0044 +0048log σMOST1 U(minus9 minus3) minus6685 minus0059 +0064log σMOST2 U(minus9 minus3) minus7227 minus0051 +0051log σMOST3 U(minus9 minus3) minus6710 minus0122 +0149

Notes U(A B) represents a uniform distribution between A and B and N (μ σ ) represents a normal distribution with mean μ andstandard deviation σ The limb-darkening coefficients q1 and q2 are defined according to the parameterization of Kipping (2013) Alllogarithms are base e

(This table is available in its entirety in FITS format)

11


gaseous envelope the planet started with would have evaporatedover its lifetime

In terms of mass and radius this planet is similar to Kepler-68 b (83 Moplus 231 Roplus Gilliland et al 2013) and HD 97658 b(79 Moplus 23 Roplus Howard et al 2011 Dragomir et al 2013) butit is likely slightly larger HIP 116454 b and HD 97658 b (Teq asymp730 K) have similar effective temperatures but Kepler-68 b(Teq asymp 1250 K under the same assumptions) is somewhat hotterLike these planets HIP 116454 b has a density intermediate tothat of rocky planets and of ice giant planets On the massndashradiusdiagram HIP 116454 b lies close to the 75 H2Ondash25 MgSiO3curve for solid planets It could be either a low-density solidplanet with a large fraction of H2O or other volatiles (whichhave equations of state similar to H2O) or it could have a densecore with a thick gaseous layer

We made inferences about the structure and composition ofHIP 116454 b if it indeed has a dense core and thick gaseousenvelope using analytic power-law fits to the results of Lopezamp Fortney (2014) Assuming that the thick gaseous envelopeis composed of hydrogen and helium in solar abundances anequilibrium temperature calculated with perfect heat redistribu-tion and an albedo of 0 and a stellar age of about 2 Gyr themodels predict that HIP 116454 b has a hydrogen and heliumenvelope making up about 05 of the planetrsquos mass The modelsuggests that HIP 116454 b has a 18 Roplus core with virtually allof the planetrsquos mass surrounded by a gaseous envelope withthickness 035 Roplus and a radiative upper atmosphere also withthickness 035 Roplus Using different assumptions to calculate theequilibrium temperature like imperfect heat distribution and anonzero albedo (for instance the value of Sheets amp Deming2014) and different assumptions about the envelopersquos composi-tion and age does not change the calculated thickness and massof the gaseous envelope by more than a factor of two We notethat this envelope fraction is consistent with the population ofKepler super-Earth and sub-Neptune-sized planets studied byWolfgang amp Lopez (2014) who found the envelope fraction ofthese candidates to be distributed around 1 with a scatter of05 dex

We also explored the composition of HIP 116454 b assumingit is solid and has little in the way of a gaseous envelope usingan online tool32 based on the model grids of Zeng amp Sasselov(2013) We investigated a three-component model with layersof H2O MgSiO3 and Fe In this case HIP 116454 b must havea significant fraction of either H2O or other volatiles in an iceform like methane or ammonia The composition in this casewould be more similar to the ice giants in the solar system thanthe rocky planets like Earth

We find that the pressure at the core of the planet can rangefrom 1400 GPa for an iron-free planet to 2800 GPa for asilicate-free planet Assuming a ratio of iron to silicates similarto that of the Earth and other solar system bodies we findthat the core pressure of HIP 116454 b is about 2400 GPaUnder this assumption HIP 116454 b would consist of 8 Fe17 MgSiO3 and 75 H2O by mass Using the ratio of ironto silicates in solar system bodies is usually a relatively goodassumption because this ratio is largely determined by elementsynthesis cosmochemistry which does not vary greatly on thescale of 50 parsecs However HIP 116454rsquos unusual spacemotion indicates that it might have formed elsewhere in thegalaxy so this assumption might not hold More detailed spectralanalysis in particular measuring elemental abundances for Mg

32 httpwwwastrozengcom

and Si compared to Fe in the parent star could put additionalconstraints on the composition of HIP 116454 b assumingit is solid

If solid HIP 116454 b would be one of the ldquoH2O richrdquoplanets described in Zeng amp Sasselov (2014) for which it ispossible to make inferences about the phase of the planetrsquosH2O layer given knowledge of the starrsquos age Various evidencepoints to HIP 116454 having an age of approximately 2 GyrUsing relations from Mamajek amp Hillenbrand (2008) the Rprime

HKlevel indicates an age of 27 Gyr and the rotation indicatesan age of 11 Gyr if the rotation period is indeed close to16 days The white dwarfrsquos cooling age however sets a lowerlimit of approximately 13 Gyr Future observations like a massmeasurement of the white dwarf to estimate its progenitorrsquosmass (and therefore age on the main sequence) could constrainthe age further If HIP 116454rsquos age is indeed about 2 Gyr andthe planet lacks a gaseous envelope then it is likely to have waterin plasma phases near its waterndashsilicate boundary (the bottomof the H2O layer) but if it is slightly older (sim3 Gyr or more)or has a faster cooling rate it could have superionic phases ofwater

42 Suitability for Follow-up Observations

HIP 116454 b is a promising transiting super-Earth for follow-up observations because of the brightness of its star especiallyin the near infrared We used the Exoplanet Orbit Database33

(Wright et al 2011 Han et al 2014) to compare HIP 116454 b toother transiting sub-Neptune-sized planets orbiting bright starsWe found that among stars hosting transiting sub-Neptunes withRp lt 3 Roplus only Kepler 37 55 Cnc and HD 97658 havebrighter K-band magnitudes

HIP 116454 is particularly well suited for additional follow-up photometric and RV observations both to measure the massof the planet to higher precision and to search for more planets inthe system HIP 116454 is chromospherically inactive and haslow levels of stellar RV jitter (045 plusmn 029 m sminus1) This combinedwith its brightness makes it an efficient RV target Moreover thebrightness of the host star makes HIP 116454 ideal for follow-upwith the upcoming CHEOPS mission (Broeg et al 2013)

HIP 116454 b could be important in the era of the James WebbSpace Telescope to probe the transition between ice giants androcky planets In the solar system there are no planets with radiibetween 1ndash3 Roplus while population studies with Kepler data haveshown these planets to be nearly ubiquitous (Howard et al 2012Fressin et al 2013 Petigura et al 2013 Morton amp Swift 2014)Atmospheric studies with transit transmission spectroscopy canhelp determine whether these planets are in fact solid or havea gaseous envelope and give a better understanding of howthese planets form and why they are so common in the GalaxyAlso of interest is the fact that HIP 116454 b is very similarto HD 97658 b in terms of its orbital characteristics (both arein sim10 day low-eccentricity orbits) mass and radius (within10 in radius and within 25 in mass) and stellar hosts(both orbit K dwarfs) Comparative studies of these two super-Earths will be valuable for understanding the diversity andpossible origins of close-in super-Earths around Sun-like starsThis being said despite HIP 116454rsquos brightness the relativelyshallow transit depth will make it a somewhat less efficient targetthan super-Earths orbiting smaller stars (for instance GJ 1214 bCharbonneau et al 2009)

33 httpwwwexoplanetsorg

12


43 Implications for K2 Science

HIP 116454 b has demonstrated the potential of K2 to increasethe number of bright transiting planets amenable to radialvelocity follow-up Despite its degraded pointing precision itis possible to calibrate and correct K2 data to the point wheresuper-Earths can be detected to high significance with only onetransit Despite the increased expense of bright stars in terms ofKepler target pixels required for the aperture K2 data is of highenough precision to produce many transiting exoplanets aroundbright stars

Many K2 fields including the engineering test field arelocated such that observatories in both hemispheres can viewthe stars a significant difference between K2 and the originalKepler mission Even though all of our follow-up observationsfor HIP 116454 b took place at northern observatories the starrsquosequatorial location enables follow-up from southern facilitieslike the original HARPS instrument at La Silla Observatory(Mayor et al 2003) and the Planet Finding Spectrograph atLas Campanas Observatory (Crane et al 2010) just as easilyas with northern facilities with instruments like HARPS-N orthe High Resolution Echelle Spectrograph at Keck Observatory(Vogt et al 1994)

Many Kepler planet candidates were confirmed in part thanksto precise measurements of the Kepler image centroid as theplanet transited the expected motion of the image centroidcould be calculated based on the brightness and position ofother stars near the aperture and deviations from that predictioncould signal the presence of a false-positive planet candidateSuch an analysis will be substantially more difficult for K2data because the unstable pointing leads to large movements ofthe image centroid In this work we were able to exclude thepossibility of background objects creating false transit signalstaking advantage of the starrsquos high proper motion and archivalimaging This will be more difficult for more distant starsHowever the focus of the K2 mission on nearby late K andM dwarfs which typically have high proper motions couldmake this technique of background star exclusion more widelyapplicable than it was for the original Kepler mission

We thank Ball Aerospace and the KeplerK2 team for theirbrilliant and tireless efforts to make the K2 mission a possibilityand a success Without their work this result would not havebeen possible We thank Sarah Ballard and Kevin Apps forhelpful conversations We acknowledge many helpful commentsfrom our anonymous reviewer as well as from Eric Feigelsonour scientific editor

Some of the data presented in this paper were obtained fromthe Mikulski Archive for Space Telescopes (MAST) STScIis operated by the Association of Universities for Research inAstronomy Inc under NASA contract NAS5-26555 Supportfor MAST for non-HST data is provided by the NASA Officeof Space Science via grant NNX13AC07G and by other grantsand contracts This paper includes data collected by the Keplermission Funding for the Kepler mission is provided by theNASA Science Mission directorate

This research has made use of NASArsquos AstrophysicsData System the SIMBAD database and VizieR catalog ac-cess tool operated at CDS Strasbourg France the Ex-oplanet Orbit Database and the Exoplanet Data Explorerat httpwwwexoplanetsorg PyAstronomy the repositoryand documentation for which can be found at httpsgithubcomsczeslaPyAstronomy and the NASA Exoplanet

Archive which is operated by the California Institute of Tech-nology under contract with the National Aeronautics and SpaceAdministration under the Exoplanet Exploration Program

AV and BTM are supported by the National ScienceFoundation Graduate Research Fellowship grants No DGE1144152 and DGE 1144469 respectively JAJ is supported bygenerous grants from the David and Lucile Packard and Alfred PSloan Foundations CB acknowledges support from the AlfredP Sloan Foundation PF acknowledges support by Fundacaopara a Ciencia e a Tecnologia (FCT) through Investigador FCTcontracts of reference IF010372013 and POPHFSE (EC) byFEDER funding through the program ldquoPrograma Operacionalde Factores de CompetitividadendashCOMPETErdquo WWW wassupported by the Austrian Science Fund (FWF P22691-N16)The research leading to these results has received funding fromthe European Union Seventh Framework Programme (FP72007-2013) under grant Agreement No 313014 (ETAEARTH)This publication was made possible through the support ofa grant from the John Templeton Foundation The opinionsexpressed in this publication are those of the authors and do notnecessarily reflect the views of the John Templeton Foundation

This work is based on observations made with the ItalianTelescopio Nazionale Galileo (TNG) operated on the island ofLa Palma by the Fundacin Galileo Galilei of the INAF (IstitutoNazionale di Astrofisica) at the Spanish Observatorio del Roquede los Muchachos of the Instituto de Astrofisica de CanariasThe HARPS-N project was funded by the Prodex program ofthe Swiss Space Office (SSO) the Harvard University Originof Life Initiative (HUOLI) the Scottish Universities PhysicsAlliance (SUPA) the University of Geneva the SmithsonianAstrophysical Observatory (SAO) and the Italian NationalAstrophysical Institute (INAF) University of St AndrewsQueens University Belfast and University of Edinburgh

The Robo-AO system is supported by collaborating part-ner institutions the California Institute of Technology andthe Inter-University Centre for Astronomy and Astrophysicsand by the National Science Foundation under grant NosAST-0906060 AST-0960343 and AST-1207891 by the MountCuba Astronomical Foundation by a gift from Samuel Oschin

Some of the data presented herein were obtained at theWM Keck Observatory which is operated as a scientificpartnership among the California Institute of Technology theUniversity of California and the National Aeronautics andSpace Administration The observatory was made possible bythe generous financial support of the WM Keck FoundationThe authors wish to recognize and acknowledge the verysignificant cultural role and reverence that the summit of MaunaKea has always had within the indigenous Hawaiian communityWe are most fortunate to have the opportunity to conductobservations from this mountain

WASP-South is hosted by the SAAO and SuperWASP by theIsaac Newton Group and the Instituto de Astrofısica de Canariaswe gratefully acknowledge their ongoing support and assistanceFunding for WASP comes from consortium universities andfrom the UKrsquos Science and Technology Facilities Council(STFC)

The Digitized Sky Surveys were produced at the SpaceTelescope Science Institute under US Government grant NAGW-2166 The images of these surveys are based on photographicdata obtained using the Oschin Schmidt Telescope on PalomarMountain and the UK Schmidt Telescope The plates wereprocessed into the present compressed digital form with thepermission of these institutions

13


The National Geographic SocietyndashPalomar Observatory SkyAtlas (POSS-I) was made by the California Institute of Tech-nology with grants from the National Geographic Society TheSecond Palomar Observatory Sky Survey (POSS-II) was madeby the California Institute of Technology with funds from theNational Science Foundation the National Geographic Societythe Sloan Foundation the Samuel Oschin Foundation and theEastman Kodak Corporation The Oschin Schmidt Telescope isoperated by the California Institute of Technology and PalomarObservatory

Funding for SDSS-III has been provided by the Alfred PSloan Foundation the participating institutions the NationalScience Foundation and the US Department of Energy Officeof Science The SDSS-III web site is httpwwwsdss3org

SDSS-III is managed by the Astrophysical Research Consor-tium for the participating institutions of the SDSS-III Collabo-ration including the University of Arizona the Brazilian Par-ticipation Group Brookhaven National Laboratory CarnegieMellon University University of Florida the French Participa-tion Group the German Participation Group Harvard Univer-sity the Instituto de Astrofisica de Canarias the Michigan StateNotre DameJINA Participation Group Johns Hopkins Univer-sity Lawrence Berkeley National Laboratory Max Planck Insti-tute for Astrophysics Max Planck Institute for ExtraterrestrialPhysics New Mexico State University New York UniversityOhio State University Pennsylvania State University Univer-sity of Portsmouth Princeton University the Spanish Participa-tion Group University of Tokyo University of Utah VanderbiltUniversity University of Virginia University of Washingtonand Yale University

Facilities Kepler MOST FLWO15m (CfA DigitalSpeedometer TRES) TNG (HARPS-N) PO15m (Robo-AO)PO12m KeckII (NIRC2)

REFERENCES

Abazajian K N Adelman-McCarthy J K Agueros M A et al 2009 ApJS182 543

Abell G O 1955 PASP 67 258Akeson R L Chen X Ciardi D et al 2013 PASP 125 989Ambikasaran S Foreman-Mackey D Greengard L Hogg D W amp OrsquoNeil

M 2014 arXiv14036015Ballard S Chaplin W J Charbonneau D et al 2014 ApJ 790 12Ballard S Charbonneau D Deming D et al 2010 PASP 122 1341Baranec C Riddle R Law N M et al 2014 ApJL 790 L8Baranne A Queloz D Mayor M et al 1996 AampAS 119 373Barclay T Rowe J F Lissauer J J et al 2013 Natur 494 452Batalha N M Rowe J F Bryson S T et al 2013 ApJS 204 24Borucki W J Koch D G Basri G et al 2011 ApJ 736 19Bowler B P Liu M C Shkolnik E L et al 2012 ApJ 753 142Broeg C Fortier A Ehrenreich D et al 2013 EPJWC 47 3005Buchhave L A Latham D W Johansen A et al 2012 Natur 486 375Charbonneau D Berta Z K Irwin J et al 2009 Natur 462 891Charbonneau D Brown T M Noyes R W amp Gilliland R L 2002 ApJ

568 377

Cosentino R Lovis C Pepe F et al 2012 Proc SPIE 8446 84461VCrane J D Shectman S A Butler R P et al 2010 Proc SPIE 7735 773553da Silva L Girardi L Pasquini L et al 2006 AampA 458 609Dawson R I amp Fabrycky D C 2010 ApJ 722 937Dragomir D Matthews J M Eastman J D et al 2013 ApJL 772 L2Dumusque X Bonomo A S Haywood R D et al 2014 ApJ 789 154Eastman J Gaudi B S amp Agol E 2013 PASP 125 83Egret D Didelon P McLean B J Russell J L amp Turon C 1994 yCat

1197 0Foreman-Mackey D Hogg D W Lang D amp Goodman J 2013 PASP

125 306Foreman-Mackey D Hoyer S Bernhard J amp Angus R 2014 georg Georg

(v020) Zenodo doi105281zenodo11989Fressin F Torres G Charbonneau D et al 2013 ApJ 766 81Gansicke B T 1997 PhD thesis Universitat GottingenGeweke J 1992 Bayesian Stat 169Gilliland R L Marcy G W Rowe J F et al 2013 ApJ 766 40Goodman J amp Weare J 2010 Commun Appl Math Comput Sci 5 65Han E Wang S X Wright J T et al 2014 PASP 126 827Howard A W Johnson J A Marcy G W et al 2011 ApJ 730 10Howard A W Marcy G W Bryson S T et al 2012 ApJS 201 15Howell S B Sobeck C Haas M et al 2014 PASP 126 398Kipping D M 2013 MNRAS 435 2152Knutson H A Dragomir D Kreidberg L et al 2014 ApJ 794 155Kreidberg L Bean J L Desert J-M et al 2014 Natur 505 69Latham D W Stefanik R P Torres G et al 2002 AJ 124 1144Law N M Morton T Baranec C et al 2014 ApJ 791 35Lopez E D amp Fortney J J 2014 ApJ 792 1Mamajek E E amp Hillenbrand L A 2008 ApJ 687 1264Mandel K amp Agol E 2002 ApJL 580 L171Marcy G W Isaacson H Howard A W et al 2014 ApJS 210 20Mayor M Pepe F Queloz D et al 2003 Msngr 114 20Mestel L 1952 MNRAS 112 583Morton T D amp Swift J 2014 ApJ 791 10Muirhead P S Johnson J A Apps K et al 2012 ApJ 747 144Pepe F Mayor M Galland F et al 2002 AampA 388 632Petigura E A Marcy G W amp Howard A W 2013 ApJ 770 69Pollacco D L Skillen I Collier Cameron A et al 2006 PASP

118 1407Richmond M W Droege T F Gombert G et al 2000 PASP 112 397Rogers L A 2014 arXiv14074457Rowe J F Matthews J M Kuschnig R et al 2006 MmSAI 77 282Scargle J D 1982 ApJ 263 835Schwarz G 1978 Ann Stat 6 461Sheets H A amp Deming D 2014 ApJ 794 133Skrutskie M F Cutri R M Stiening R et al 2006 AJ 131 1163Teske J K Cunha K Schuler S C Griffith C A amp Smith V V 2013 ApJ

778 132Valencia D OrsquoConnell R J amp Sasselov D 2006 Icar 181 545Vanderburg A amp Johnson J A 2014 PASP 126 948van Horn H M 1971 in IAU Symp 42 White Dwarfs ed W J Luyten

(Cambridge Cambridge Univ Press) 97van Leeuwen F 2007 AampA 474 653Vogt S S Allen S L Bigelow B C et al 1994 Proc SPIE 2198 362Walker G Matthews J Kuschnig R et al 2003 PASP 115 1023Wolfgang A amp Lopez E 2014 arXiv14092982Wright J T Fakhouri O Marcy G W et al 2011 PASP 123 412Wright J T Marcy G W Butler R P amp Vogt S S 2004 ApJS

152 261Yelda S Lu J R Ghez A M et al 2010 ApJ 725 331Yi S Demarque P Kim Y-C et al 2001 ApJS 136 417Zeng L amp Sasselov D 2013 PASP 125 227Zeng L amp Sasselov D 2014 ApJ 784 96

14

Claret A amp Bloemen S 2011 yCat 352 99075

e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION

41 Composition of HIP116454b



REFERENCES


an extended mission called K2 was enabled by pointing alongthe ecliptic plane and balancing the spacecraft against solarradiation pressure to mitigate the instability caused by the failedreaction wheels The recently extended K2 mission enablesrenewed opportunities for transit science on a new set of brighttarget stars albeit with somewhat reduced photometric precisioncompared to the original Kepler mission (Howell et al 2014)

Searching for transiting exoplanets around bright nearbystars is important because measuring the precise masses andradii of transiting planets allows for characterization of theirinterior structures and atmospheres (Charbonneau et al 2002Rogers 2014 Knutson et al 2014 Teske et al 2013 Kreidberget al 2014) This is particularly desirable for planets withmasses intermediate to those of the Earth and Uranus commonlyreferred to as super-Earths because no such planet exists in oursolar system (Valencia et al 2006) However while the radiiof Kepler planets are often measured to high precision (Ballardet al 2014) their masses are generally unknown because thehost stars are faint (V gt 12) and exposure times needed forradial velocity (RV) measurements are prohibitive for all but thebrightest Kepler planet candidates (eg Dumusque et al 2014Marcy et al 2014)

Preparations for the extended two-wheeled Kepler missionincluded a 9 day test of the new observing mode in February of2014 After the data were released to the public Vanderburg ampJohnson (2014 hereafter VJ14) presented a photometric reduc-tion technique that accounts for the motion of the spacecraftimproves photometric precision of raw K2 data by a factor of2ndash5 and enables photometric precision comparable to that ofthe original Kepler mission

While the data collected during the engineering test wereintended primarily as a test of the new spacecraft operatingmode an inspection of light curves produced with this techniquenonetheless revealed a single transit event in engineering datataken of HIP 116454 In this paper we provide an analysis ofthat light curve along with archival and follow-up spectroscopyarchival and adaptive optics imaging RV measurements fromthe HARPS-N spectrograph and photometric observations fromthe Wide Angle Search for Planets (WASP) survey and theMicrovariability and Oscillations of STars (MOST) space tele-scope These measurements allow us to verify and characterizethe first planet discovered by the two-wheeled Kepler missiona new transiting super-Earth orbiting the bright nearby high-proper-motion K dwarf HIP 116454

2 DATA AND ANALYSIS

21 K2 Photometry

HIP 116454 and nearly 2000 other stars were observed by theKepler spacecraft from 2014 February 4 until 2014 February 12during the Kepler Two-Wheel Concept Engineering Test Afterthe first 25 days of the test Kepler underwent a large intentionaladjustment to its pointing to move its target stars to the centerof their apertures where they stayed for the last 65 days of thetest We downloaded the full engineering test data set from theMikulski Archive for Space Telescopes (MAST) and reducedthe Kepler target pixel files as described in VJ14

In brief we extracted raw aperture photometry and imagecentroid positions from the Kepler target pixel files Raw K2photometry is dominated by jagged events corresponding to themotion of the spacecraft as Keplerrsquos pointing drifts becauseof solar radiation pressure and is periodically corrected withthrusters For the last 65 days after the large pointing tweak we

Table 1Astrometric and Photometric Properties of HIP 116454

Parameter Value Uncertainty Source

α (J2000) 23 35 4928 Hipparcos a

δ (J2000) +00 26 4386 Hipparcosμα (mas yrminus1) minus2380 17 Hipparcosμδ (mas yrminus1) minus1859 09 Hipparcosπ (mas) 181 172 HipparcosB 1108 001 TychoV 10190 0009 Tycho b

R 971 003 TASSc

I 925 003 TASSu 14786 002 SDSSd

g 10837 002 SDSSr 9908 002 SDSSi 9680 002 SDSSJ 860 002 2MASSe

H 814 003 2MASSKS 803 002 2MASS

Notesa van Leeuwen (2007)b Egret et al (1994)c Richmond et al (2000)d Abazajian et al (2009)e Skrutskie et al (2006)

removed the systematics due to the motion of the spacecraft bycorrelating the measured flux with the image centroid positionsmeasured from photometry We essentially produced a ldquoselfflat fieldrdquo (SFF) similar to those produced by for instanceBallard et al (2010) for analysis of Spitzer photometry We fita piecewise linear function to the measured dependence of fluxon centroid position with outlier exclusion to preserve transitevents and removed the dependence on centroid position fromthe raw light curve Similar to VJ14 we excluded data pointstaken while Keplerrsquos thrusters were firing from our reducedlight curves because these data were typically outliers from thecorrected light curves For HIP 116454 the median absolutedeviation (MAD) of the 30-minute-long cadence data pointsimproved from 500 parts per million (ppm) for the raw lightcurve to 50 ppm for the SFF light curve

Visual inspection of light curves from the 2000 targetsobserved during the engineering test revealed a 1 millimagnitude(mmag) deep candidate transit in photometry of HIP 116454designated EPIC 60021410 by the Kepler team HIP 116454rsquosphotometric and astrometric measurements are summarized inTable 1 Raw and corrected K2 photometry for HIP 116454are shown in Figure 1 We fit a Mandel amp Agol (2002) modelto the transit and measured a total duration of approximately225 hr and a planet-to-star radius ratio of approximately 003Unfortunately the data point during transit ingress happenedduring a thruster firing event and was excluded by our pipelineThis particular data point does not appear to be anomalous butwe choose to exclude it to minimize risk of contaminating thetransit with an outlier Slow photometric variability presumablydue to starspot modulation is evident in the K2 light curve atthe subpercent level

We also performed a similar SFF correction to the data takenin the 25 days of data before the large pointing tweak Eventhough the resulting data quality is somewhat worse we are ableto confidently exclude any other events of a similar depth duringthat time

Because K2 only observed one transit event we were notable to measure a precise orbital period for the planet candidate

2


1862 1864 1866 1868 1870BJD - 2454833

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22 Imaging






222 Modern Imaging


3








4

















5



0

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P = 00001




radice sin(ω) and



radice sin(ω) and



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e sin(ω) andradic



2020 2040 2060 2080 2100BJD minus 2454833 [days]

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0

5

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Rad

ial V

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ity [m

sminus1 ]

RMS = 126 msminus1

91 Day Period


minus10

minus5

0

5

10

RV

[msminus

1 ]

45 Day Period


minus6minus4minus2

0246

RV

[msminus

1 ]


6


1862 1864 1866 1868BJD - 2454833 [days]

09985

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1862 1864 1866 1868BJD - 2454833 [days]

09985

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10005

10010

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ness






25 Photometry

251 WASP


252 MOST









7



0996

0998

1000

1002

1004

Rel

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e B

right

ness

K2

MOST














8



10 20 30 40 50Period [days]

02

4

6

8

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12

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P = 001


0 10 20 30 40 50Lag [days]

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020

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10 20 30 40 50Period [days]

02

4

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0 10 20 30 40 50Lag [days]

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de


10 20 30 40 50Period [days]

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4

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P = 001


0 10 20 30 40 50Lag [days]

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9




Orbital parameters


Stellar parameters


Planet parameters


R2a

)12 (K) 690 plusmn 14 B C D E






4 DISCUSSION



10











11

















12
















13






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES


1862 1864 1866 1868 1870BJD - 2454833

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22 Imaging






222 Modern Imaging


3








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P = 00001




radice sin(ω) and



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andradic


e sin(ω) andradic



2020 2040 2060 2080 2100BJD minus 2454833 [days]

minus10

minus5

0

5

10

Rad

ial V

eloc

ity [m

sminus1 ]

RMS = 126 msminus1

91 Day Period


minus10

minus5

0

5

10

RV

[msminus

1 ]

45 Day Period


minus6minus4minus2

0246

RV

[msminus

1 ]


6


1862 1864 1866 1868BJD - 2454833 [days]

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1862 1864 1866 1868BJD - 2454833 [days]

09985

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25 Photometry

251 WASP


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7



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1000

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right

ness

K2

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8



10 20 30 40 50Period [days]

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P = 001


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10 20 30 40 50Period [days]

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4

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P = 001


0 10 20 30 40 50Lag [days]

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005

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020

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⎡⎣minus sin2

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)g2

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⎤⎦ (1)








9




Orbital parameters


Stellar parameters


Planet parameters


R2a

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4 DISCUSSION



10











11

















12
















13






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES








4

















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2020 2040 2060 2080 2100BJD minus 2454833 [days]

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Rad

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sminus1 ]

RMS = 126 msminus1

91 Day Period


minus10

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6


1862 1864 1866 1868BJD - 2454833 [days]

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1862 1864 1866 1868BJD - 2454833 [days]

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25 Photometry

251 WASP


252 MOST









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1000

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right

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K2

MOST














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10 20 30 40 50Period [days]

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9




Orbital parameters


Stellar parameters


Planet parameters


R2a

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4 DISCUSSION



10











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568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES

















5



0

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P = 00001




radice sin(ω) and



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e sin(ω) andradic



2020 2040 2060 2080 2100BJD minus 2454833 [days]

minus10

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Rad

ial V

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sminus1 ]

RMS = 126 msminus1

91 Day Period


minus10

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45 Day Period


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6


1862 1864 1866 1868BJD - 2454833 [days]

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1862 1864 1866 1868BJD - 2454833 [days]

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9




Orbital parameters


Stellar parameters


Planet parameters


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4 DISCUSSION



10











11

















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REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES



0

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P = 00001




radice sin(ω) and



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2020 2040 2060 2080 2100BJD minus 2454833 [days]

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Rad

ial V

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sminus1 ]

RMS = 126 msminus1

91 Day Period


minus10

minus5

0

5

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RV

[msminus

1 ]

45 Day Period


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0246

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[msminus

1 ]


6


1862 1864 1866 1868BJD - 2454833 [days]

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1862 1864 1866 1868BJD - 2454833 [days]

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25 Photometry

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10 20 30 40 50Period [days]

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⎤⎦ (1)








9




Orbital parameters


Stellar parameters


Planet parameters


R2a

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4 DISCUSSION



10











11

















12
















13






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES


1862 1864 1866 1868BJD - 2454833 [days]

09985

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09995

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10005

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right

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1862 1864 1866 1868BJD - 2454833 [days]

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25 Photometry

251 WASP


252 MOST









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⎤⎦ (1)








9




Orbital parameters


Stellar parameters


Planet parameters


R2a

)12 (K) 690 plusmn 14 B C D E






4 DISCUSSION



10











11

















12
















13






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES



0996

0998

1000

1002

1004

Rel

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K2

MOST














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10 20 30 40 50Period [days]

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plitu

de


10 20 30 40 50Period [days]

02

4

6

8

10

12

L-S

Pow

er

P = 001


0 10 20 30 40 50Lag [days]

000

005

010

015

020

Am

plitu

de


10 20 30 40 50Period [days]

02

4

6

8

10

12

L-S

Pow

er

P = 001


0 10 20 30 40 50Lag [days]

000

005

010

015

020

Am

plitu

de



kij = A2 exp


2l2

]exp

⎡⎣minus sin2

(π (ximinusxj )

P

)g2

q

⎤⎦ (1)








9




Orbital parameters


Stellar parameters


Planet parameters


R2a

)12 (K) 690 plusmn 14 B C D E






4 DISCUSSION



10











11

















12
















13






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES



10 20 30 40 50Period [days]

02

4

6

8

10

12

L-S

Pow

er

P = 001


0 10 20 30 40 50Lag [days]

000

005

010

015

020

Am

plitu

de


10 20 30 40 50Period [days]

02

4

6

8

10

12

L-S

Pow

er

P = 001


0 10 20 30 40 50Lag [days]

000

005

010

015

020

Am

plitu

de


10 20 30 40 50Period [days]

02

4

6

8

10

12

L-S

Pow

er

P = 001


0 10 20 30 40 50Lag [days]

000

005

010

015

020

Am

plitu

de



kij = A2 exp


2l2

]exp

⎡⎣minus sin2

(π (ximinusxj )

P

)g2

q

⎤⎦ (1)








9




Orbital parameters


Stellar parameters


Planet parameters


R2a

)12 (K) 690 plusmn 14 B C D E






4 DISCUSSION



10











11

















12
















13






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES




Orbital parameters


Stellar parameters


Planet parameters


R2a

)12 (K) 690 plusmn 14 B C D E






4 DISCUSSION



10











11

















12
















13






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES











11

















12
















13






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES

















12
















13






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES
















13






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES






REFERENCES




568 377









14


e e

1 INTRODUCTION

2 DATA AND ANALYSIS

21 K2 Photometry

22 Imaging



25 Photometry




4 DISCUSSION




REFERENCES

characterizing k2 planet discoveries: a …lzeng/papers/apj_800_1_59.pdf13 instituto de...

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