Finding High Quality Young Star Candidates in Ceph C using ...
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1 Finding High Quality Young Star Candidates in Ceph C using X-ray, Optical, and IR data Mentor Teacher: Laura Orr, Ukiah School, Ukiah, OR Alexandra Miller, Milken Community Schools, Los Angeles, CA Milton Johnson, Bioscience High School, Phoenix, AZ Mentor Astronomer: Luisa Rebull, IRSA/SSC, IPAC, Caltech, Pasadena, CA 1. Abstract This study will be looking for new candidate young stars within the star forming region of Ceph OB3, more specifically in a region of this molecular cloud called Ceph C. Even though this region lies in the galactic plane and is included serendipitously in several large galactic plane surveys, Ceph C has not been well studied in the past, and few young stellar objects (YSOs) have been identified there. The YSOVAR team (Rebull et al. 2014) has time-series monitoring data of this region, and in order to understand the diversity of light curves, it is crucial to understand which objects in the field of view are likely YSOs, and which are foreground/background objects. The goal of our study is to identify candidate YSO sources as well as support the greater understanding of the variety, evolution, and variability of young stars. Our search for young stars will use X-ray, optical, and IR data from Chandra, SDSS, IPHAS, 2MASS, Spitzer (IRAC and MIPS), WISE, Herschel, and the literature (including SCUBA data), giving us a wavelength data range from 0.001 to 850 microns. We will merge the catalogs across all available wavelengths. We will make color-color and color magnitude diagrams for the objects in the region, and use IR colors, X- rays, and variability properties to identify candidate YSOs. We will inspect images (where possible) to ensure good matches across wavelengths and to identify (and remove) resolved galaxies. We will also construct spectral energy distribution diagrams (SEDs) for each candidate YSO in order to better assess whether or not the objects are likely reliable YSOs. 2.0 Science Introduction and Context 2.1 Star Formation Stars form from clouds of interstellar gas and dust that have slowly coalesced with gravity and time. The inward gravitational collapse combined with the rotational angular momentum of the cloud form a cocoon and then a disk around the center mass. The heat generated from this gravitational collapse radiates outward, heating the surrounding dust cloud. The cloud then provides its own IR emission, in addition to that of the star. This excess IR emission causes the YSO spectral energy distribution (SED) to deviate from the standard blackbody emission spectrum, thus providing the IR excess that is characteristic of young stars. These young stars are also rotating fast, accreting high amounts of material,
Transcript of Finding High Quality Young Star Candidates in Ceph C using ...
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FindingHighQualityYoungStarCandidatesinCephCusingX-ray,Optical,andIRdataMentorTeacher:LauraOrr,UkiahSchool,Ukiah,ORAlexandraMiller,MilkenCommunitySchools,LosAngeles,CAMiltonJohnson,BioscienceHighSchool,Phoenix,AZMentorAstronomer:LuisaRebull,IRSA/SSC,IPAC,Caltech,Pasadena,CA1.Abstract ThisstudywillbelookingfornewcandidateyoungstarswithinthestarformingregionofCephOB3,morespecificallyinaregionofthismolecularcloudcalledCephC.Eventhoughthisregionliesinthegalacticplaneandisincludedserendipitouslyinseverallargegalacticplanesurveys,CephChasnotbeenwellstudiedinthepast,andfewyoungstellarobjects(YSOs)havebeenidentifiedthere.TheYSOVARteam(Rebulletal.2014)hastime-seriesmonitoringdataofthisregion,andinordertounderstandthediversityoflightcurves,itiscrucialtounderstandwhichobjectsinthefieldofviewarelikelyYSOs,andwhichareforeground/backgroundobjects.ThegoalofourstudyistoidentifycandidateYSOsourcesaswellassupportthegreaterunderstandingofthevariety,evolution,andvariabilityofyoungstars.OursearchforyoungstarswilluseX-ray,optical,andIRdatafromChandra,SDSS,IPHAS,2MASS,Spitzer(IRACandMIPS),WISE,Herschel,andtheliterature(includingSCUBAdata),givingusawavelengthdatarangefrom0.001to850microns.Wewillmergethecatalogsacrossallavailablewavelengths.Wewillmakecolor-colorandcolormagnitudediagramsfortheobjectsintheregion,anduseIRcolors,X-rays,andvariabilitypropertiestoidentifycandidateYSOs.Wewillinspectimages(wherepossible)toensuregoodmatchesacrosswavelengthsandtoidentify(andremove)resolvedgalaxies.Wewillalsoconstructspectralenergydistributiondiagrams(SEDs)foreachcandidateYSOinordertobetterassesswhetherornottheobjectsarelikelyreliableYSOs.2.0ScienceIntroductionandContext2.1StarFormation
Starsformfromcloudsofinterstellargasanddustthathaveslowlycoalescedwithgravityandtime.Theinwardgravitationalcollapsecombinedwiththerotationalangularmomentumofthecloudformacocoonandthenadiskaroundthecentermass.Theheatgeneratedfromthisgravitationalcollapseradiatesoutward,heatingthesurroundingdustcloud.ThecloudthenprovidesitsownIRemission,inadditiontothatofthestar.ThisexcessIRemissioncausestheYSOspectralenergydistribution(SED)todeviatefromthestandardblackbodyemissionspectrum,thusprovidingtheIRexcessthatischaracteristicofyoungstars.Theseyoungstarsarealsorotatingfast,accretinghighamountsofmaterial,
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andhaveactivechromospheres,resultingincomplexmagneticfieldsandtheemissionofhighenergyX-rays.Asprotostellarevolutioncontinues,thisdustcloudcontinuestoflattenoutandthestarbecomeslessembedded.TheamountofIRexcessmeasureddecreasesandtheSEDbecomesmoreandmorelikeatraditionalblackbodyspectrum.
Figure1:Low-massstarformationwithSEDs.(FigureadaptedfromBachiller1996andAndre&Montmerle1994.)Theillustrationsontheleftarecartoonsofthestages.TheplotsontherightareillustrativeSEDs,showingtheIRexcessabovethestellarblackbody.Nomenclatureinthisfieldcanbecomplicated,soavarietyofnamesofstagesisprovidedinthefigure.TheSEDsareClass0(alsocalledprotostar),ClassI,Flat,ClassII(alsocalledclassicalTTauristars,orCTTS),andClassIII(alsocalledweak-linedTTauristars,orWTTS).Sometimes‘transitiondisk’isusedtorefertothestatebetweenhavingasubstantialdiskandhavingatenuousdisk.Thelast,mosttenuousdiskcanalsobecalledadebrisdisk.
AnSEDisthenetenergymeasuredasafunctionofwavelength.ForYSOs,theshape
oftheSEDcanbeempiricallyevaluatedtohelpdeterminetheclassoftheyoungstar(see,e.g.,Wilkingetal.2001).Youngstarclassesareinterpretedashowembeddedtheyoungstarisinitsformationdustcloud.BycomparingtheobservedSEDs,youngstarscanbeclassifiedandtheirrelativeageestimatedintermsoftheamountsofexcessIRenergyabovethetypicalblackbodycurve.TheslopeofSEDcurveintheneartomidIRregion(2-25𝜇m)allowsustoplacetheobjectsinSEDclasses:Class0,I,Flat,II,andIII(seeFig.1).Itisoftenassumedthattheclassificationsystemroughlycorrelatestoevolutionarysequence;Class0willtransitiontoaClass1astheircircumstellardiskisaccreted,etc.,untiltheYSObecomesvisibleinopticalwavelengthsandbecomesapre-mainsequencestar.ThemappingbetweenSEDshapeandagemaynotbesoclear-cut(see,e.g.,Robitailleetal.2006,Dunhametal.2010),butonaverage,itisthoughtthatYSOswithsteep,positiveSEDslopesareyoungerthanYSOswithstellar(negative)SEDslopes.
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2.2ScienceBackground:OurTarget MolecularcloudsaredenseandcompactregionsthroughouttheMilkyWaywheregasanddustclumptogether,anditisinthesecoldregionsthatstarsareborn.TheCepheusmolecularcloud(locatedgenerallyintheconstellationCepheus)isasiteoftriggeredstarformationduetotheinteractionofthemolecularcloudandtheexpandingHIIregionS155.Thisregion,calledCephOB3,containsindividualsub-cloudswithinthegreatercloud,referredtoasCephA-F(identifiedandlabeledbySargent1977).Theseregionsareknownareasofactivestarformationbutnotwellobservedfromground-basedopticalobservatoriesorspacebasedmissionsinthepast.ThefirstphotometricstudyoftheentireCepheusmolecularcloudwasdonebyBlaauwetal.in1964andidentified40early-typestarsinthecloudatadistanceofapproximately725parsecs.Severalotherstudiesinthe1970’s(alsophotometrybased)refinedtheBlaauwlistandexpandedittoincludefaintersources,thoughsourcesthatarestillbrightbytoday’sstandards.
Figure2:RGBimageofCephCregiontakenfromIRSAFinderChart.Red:DSS2IR,green:DSS2Red,blue:DSS2Blue.Centercoordinates23h05m51.00s+62d30m55.0sEquJ2000.Imagesize1degx1deg.
Evenwiththeavailabilityofmodernsurveysinthegalaxyplaneanddataanalysistechniques,starformationintheregionofCephC(Fig.2)hasnotbeenwellstudied;itistheleastwellstudiedofalltheCepheusclusters.Hodapp(1994)wasthefirsttodiscover
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theembeddedclusterinCephC.ThiswasaK-bandimagingsurveyofmanydifferentmolecularoutflowsources.CephCwasjustoneofmanytargets,andHodapp(1994)simplynotedthattherewasanIR-brightIRclusterinCephC.YoungstarscanalsobebrightinHα;Mikami&Ogura(2001)identifiedHαstarsintheregionbutonlyoneisinourregionofinterest(seebelow).Melikianetal.(2014)conductedanotherHαsurveyoftheCephOB3region,butnoneofthosetargetsareintheregionweareconsideringhere.Withametal.(2008)lookedforHα-brightstarsthroughouttheIPHASsurvey(whichincludesthisregion)buttheyfindonly1moreHα-brightstarinthisregionweareconsidering. Morerecently,CephCwasincludedasoneofthestarformingclustersstudiedbytheSpitzerSpaceTelescope(Werneretal.2004)aspartoftheYoungStellarClustersurvey(Megeathetal.2004).Thisstudy’sgoalsincludedunderstandingclusteringinYSOsandwaspublishedinGutermuthetal.(2009;hereafterG09).G09completedastellarclusteringstudythatincludedCephC;theypresentednewautomatedcolorselectionprocessestoidentifyandclassifycandidatesourcescomparingIRexcessacrossIRACdatabands.Fromthis,114YSOcandidateswereidentifiedintheCephCcloud.DiFrancescoetal.(2008)includedCephCinaSCUBA(SubmillimetreCommon-UserBolometerArray)survey,finding16sourcesat450and/or850µm.TheHerschelSpaceObservatorytelescopeobservedthisregioninthefarinfrared,butthosedatasetshavenotyetbeenpublished. TheYSOVARproject(Rebulletal.2014,hereafterR14)includedCephCasoneofitstargets.ThisprojectusedSpitzertomonitoradozenstar-formingregionstostudythevariabilitypropertiesoftheyoungstars.CephCwasselectedforthatstudybecauseitincludesveryembeddedstars(objectsthatwouldbeimpossibletomonitorfromthegroundduetotheirdeeplyembeddednature),andbecauseitisatahigheclipticlatitude,allowingforalong,nearlycontinuousobservingwindow(seediscussioninR14).Aspartofthatproject,somepreliminaryanalysisoftheCephClightcurveshasbeendone,butitisfarfromcomplete.Becausesolittleworkhasbeendoneinthisclustertothispoint,theworkweareproposingtodohereaspartofNITARPiscriticalforinterpretationoftheYSOVARlightcurves.VariabilitycharacteristicsareexpectedtobedifferentforYSOsofdifferentages,buttheenvironmentmayalsoplayanimportantrole.DetailedresultsobtainedfortheotherYSOVARclustersthusfar(Guentheretal.2014,Poppenhaegeretal.2015,Wolketal.2015,andRebulletal.2015)suggestintriguingdifferencesamongtheYSOVARclusters.Ifwecanobtainalistofhigh-reliabilityYSOcandidatesforCephCaspartofthisproject,wecanbetterinterpretthelightcurves--e.g.,isthisYSOlikelytohaveabigdisk,andthereforethelightcurvemorelikelytobearesultofvariationsinthediskthaninthestar.Withawell-definedlistofYSOcandidates,wecanthusunlockmanymoreofthesecretshiddenintheCephCYSOVARdata.
BecauseyoungstarsarealsooftenbrightintheX-rays,eveniftheydon’thaveanydiskslefttocreateanIRexcess,X-raysareveryusefulforidentifyingtheYSOsinaregion.TheonlyprioruseofX-raydatahereisCarkneretal.(1998),usingROSATdata,andtheydetectednothinginthisregion.AspartoftheYSOVARproject,ChandraX-rayTelescope
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dataofthisregionwasalsoobtained,buthasnotyetbeenanalyzed.ChandradataarefarmoresensitivethanROSATdata,enablingdetectionsofYSOs.BecausetheYSOVARdataisourmainmotivationforlookingforYSOshere,theregionoverwhichwewilllookforYSOsisalsotheregionoverwhichtherearelightcurves;seeFigure3.RatherthantryingtofollowthecomplicatedpolygonofYSOVARcoverage,wewillworkwithasquareabout20arcminutesonasidecenteredon23:05:51+62:30:55.
Figure3:reproducedfromR14,showingtheapproximateskycoverageforasummed-upimageconsistingofallepochsofYSOVARCephCobservations,superimposedonareversegreyscaleimageofCephCat4.5µmobtainedduringtheSpitzercryogenicmission.Thethickerbluesolidlineis3.6µmandthethickerreddashedlineis4.5µm.Asingleepochofobservationisalsoindicatedbythinnerbluesolidandreddashedlines,withthedifferencebetweenthesingleepochandthelargerpolygonduetosubstantialfieldrotationeffects(duetothelargeeclipticlatitudeofCephC;seeR14formorediscussion).TheyellowsquareistheapproximateChandracoverage.Northisupandeastistotheleft;thecenteris23:05:51+62:30:55.Thedistancebetweenthefarthestnorthandfarthestsouthcoveragehereis~20arcmin.WewillbelookingforYSOsoverthisentireregion.
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3.0AnalysisPlan 3.1Overview
Ourworkwillfocusonusingmulti-wavelengthdataforsourcesinCephC,selectingYSOcandidatesfromtheIR,X-rays,andvariability.ForthoseYSOs,wewillvisuallyinspectandassessqualityofimages,creatingcomprehensiveSEDs,andestablishingareliablelistoflikelyYSOsinCephC.Ourstudywillusedatafromseveralsources:SDSSinopticalbands(ugriz;0.29to0.9μm),IPHASintheoptical(riHα;0.6-0.8μm),2MASSinnearIR(JHKs;1.2to2.2μm),Spitzer/IRACinmidIR(3.6,4.5,5.8,and8μm),WISEinmidIR(3.4,4.6,12,and22μm),Spitzer/MIPSmidIR(24,70,and160μm),andSCUBAdatafromtheliterature(450and850μm).ThereisalsounpublishedHerscheldatahere;byeyeinthequick-lookimages,thereareseveraldetectedsources.WehavebeenincontactwiththeNHSCwhohaveagreedtoprovideusearlyaccesstotheirsourcelistsforthosedata(70,100,160,250,300,500µm).WealsohaveChandraX-raydatafromACIS(~0.001μm).
SincetheunderlyingpurposeofthisworkistoestablishareliablelistofYSOcandidatesintheregionwherewehaveYSOVARlightcurves,theboundariesofourstudyaresetbythisconstraint.TheYSOVARregioniscenteredon23:05:51+62:30:55.Includingtheserendipitouslyobtainedancillarydataaroundtheregion(seeFig.3),ourstudycoverstheregionfrom23:04:28.1+62:21:25to23:07:13.4+62:40:23,whichisaboxthatisabout20arcminutesonaside. Theanalysisprocesswillstartwithusingthe2MASS,IRAC,andMIPSdatatoidentifyobjectsthathavecolorsconsistentwithyoungstarsfollowingthemulti-colorapproachinG09.TheG09approachuses2MASS+IRAC+MIPS-24toselectYSOcandidatesbasedonaseriesofcolor-colorandcolor-magnitudediagrams.SinceYSOsareoftenbrightinX-rays,wewillincludetheX-raydatatoidentifypotentialyoungstarsthatdonothaveIRexcess.Finally,sinceYSOsareoftenvariabletoo,wewillusetheYSOVARdatatoidentifypotentialYSOs.Theimagesofallthesepotentialcandidateswillbeexaminedtoassureconsistencyacrossmanyordersofmagnitudeinwavelength,X-raysthrough850µm.Thiswillbedonethroughvisualinspectionofeachimagetoassurelocationmatchinganddeterminepointsourceclarity.WewillalsocreateopticalandIRcolor-colorandcolor-magnitudediagrams;sincetheG09approachuses2MASS+IRAC+MIPS-24,theIR-selectedYSOsareguaranteedtobeinthecorrectplaceintheIRcolor-colorandcolor-magnitudediagrams,buttheYSOsselectedviaothermeansmightnotbeinthesamelocation.TheG09approachdoesnotincludethewealthofdatafromotherwavelengths(X-ray,optical,far-IR,sub-mm)thatwehave,andwewillmakecolor-colorandcolor-magnitudediagrams(andSEDs)usingthosedatatootoidentifyhigh-confidenceYSOs. Table1isasummaryofallofthedatawehavealreadyamassed.
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Table1:Existingdata
Instrument Wavelengths SourceReductiondoneby
NumberofSources
Chandra/ACIS X-Ray(~0.001µm)collabo-rators YSOVARTeam 87
SDSSoptical,ugriz(0.29-0.9µm)
SDSSarchive SDSSarchive 3817
IPHASoptical,riHα,(0.6-0.8μm
IPHASarchive IPHASarchive 2219
2MASS JHK(1.2-2.2µm)2MASSarchive 2MASSarchive 1988
Spitzer/IRACandMIPS
MidIR(3.6,4.5,5.8,8.0,24,70µm)
collabo-rators YSOVARTeam 6100
Spitzer/IRAC MidIR(3.6,4.5µm)GLIMPSEteam
GLIMPSETeam 8271
WISEMidIR(3.4,4.6,12,22
µm)WISEarchive WISEarchive 1445
Herschel/PACSandSPIRE
FarIR(70,100,160,250,300,500µm)
Herschelarchive NHSC several(*)
SCUBA Sub-mm(450,850µm)
DiFrancescoetal.
(2008)DiFrancescoetal.(2008) 16
YSOVAR MidIR(3.6,4.5µm)collabor-ators YSOVARteam 3526
Hα-brightstars optical(0.656µm)
Mikami&Ogura(2001);Withametal.(2008)
Mikami&Ogura(2001);Withametal.
(2008) 2
(*)OnecanseeseveralsourcesintheHerschelimages,butdetailednumbersawaitamorecarefuldatareductionbyR.PaladiniandB.Schulz.
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IncontextofR14,ourteamalreadyhastheinitialIR,X-ray,andvariabilityYSOselectioncompletedasdescribedthere.Thereare283uniqueobjectsthataresoidentifiedasYSOcandidates.OtherNITARPteamshaveworkedthroughlistsofcomparablelength,soweexpectthatwewillbeabletomakeitthroughimageandSEDinspectionofall283sourcesinareasonabletime.
ThiscomprehensiveanddetailedprocesswillprovidealistofhighqualityYSOcandidatesandfullSEDsthatcanbecombinedwiththeindividuallightcurvedataforamuchbetterunderstandingofYSOvariabilitywithintheCephCregion.4.0EducationOutreach
Theteamofeducatorsworkingonthisprojectrepresentawiderangeofbackgroundsandlocations.Whiletheirteachingexperiencesandassignmentsmightbeverydifferent,theyshareanappreciationfortheeffectsscienceresearchlikethishasontheirstudents,theschoolandcommunityasawhole.Asthisprojectdevelopstheteamproposestodevelopaqualitativestudyintotheeffects,reach,andinfluenceoftheNITARPexperienceontheirstudentsandschool.Thestudywillincludeteacherobservations,mediaactivityandresponse,studentcommentsandlevelofinvolvementinscienceresearchasawhole.UkiahHighSchool(L.Orr) ForthisprojectstudentsinUkiahSchool,PilotRock,andPendletonwillbegiventheopportunitytoparticipateintheNITARPLLAMAresearchaspartofanextracurricularproject.Thebulkofourgroupworkandstudentparticipationwillbebasedonremotemeetingwithseveralinpersonworkshoptypesessionsasneeded.Overthecourseoftheprojectstudentswillgainagreaterunderstandingofstarformation,butalsoexperienceintheresearchprocess,dataanalysis,andscientificcommunication.InadditiontothecorecomponentsoftheNITARPexperience,studentswillpresenttheirworktotheschoolboardsofeachschool,atacommunitylibrarypublicoutreachnight,andtothelocal4Hastronomyclub.
LauraOrr,asaNITARPresearcher,willusetheexperiencetogainbetterunderstandingofastronomicalresearchaswellastheprocessofproposing,conducting,andpresentingauthenticresearch.Shewillsharetheexperienceandskillswithothermiddleandhighschoolteachersinherregionandstateviaworkshopsandprofessionaldevelopmentpresentationsincludingthe2016NSTANationalConvention,OSTAstateconvention,andtolocalESD.
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MilkenCommunitySchools,LosAngeles,CA–A.MillerSeveraldifferentapplicationsareplannedfortheNITARPprogramforMilken
CommunitySchools.A9thgraderplanstousehisNITARPexperiencestoinformhisparticipationintheexistingScienceResearchclass.StudentsatMilkenCommunitySchoolsin7th,8thand9thgradeswillparticipateinweeklymeetingswheretheywillworkcollaborativelytoprepareablogthatupdatesmembersofnotonlyourschoolandlocalcommunitybutpotentiallyawiderreachingeducationalcommunityontheprogressofourproject.Additionally,studentswillpresentaprotoscienceposterandthefinalscienceposterattheMilkenInnovatorXpo(MIX)inMarch2016andMarch2017.BioscienceHighSchool,Phoenix,AZ-M.Johnson
Ateamofstudentswillmeetweeklytodiscusstheongoingresearch,includinglatestprogressbyLLAMA,researchandsilldevelopmentandfutureplanning.Studentswilllearntouseastronomicalsoftwareforimageprocessing,learnresearchmethodsanddataanalysis.MembersofthisstudentteamwillalsotraveltoPasadena,Caduringthesummertobetrainedindataanalysis.
Theteamwillalsodevelopcommunicationskillsforthepurposeofbeingabletosharethescientificworkwiththepublic,viaoutreachevents.Outreacheventsmayincludepresentationsfortheschoolboard,district-widesciencedepartmentleadersandschoolprincipals.Wealsoplantopresentduringanevent(tobedetermined)atanArizonaSciTechFestivaleventinthespringof2017.5.0ResourcelistAndre,P.,&Montmerle,T.,1994,ApJ,420,837Bachiller,R.,1996,ARAA,34,111DiFrancesco,J.,etal.,2008,ApJS,175,277Dunham,M.,etal.,2010,ApJ,710,470Guenther,H.,etal.,2014,AJ,148,122Gutermuth,R.,etal.,2009,ApJSS,184,18(G09)Hodapp,K.,1994,ApJS,94,615Megeath,T.,2004,ApJS,154,367Mikami,T.,andOgura,K.,2001,Ap&SS,275,441Poppenhaeger,K.,2015,AJ,150,118Rebull,L.,etal.,2014,AJ,148,92(R14)Rebull,L.,etal.,2015,AJ,150,175Robitaille,T.P.,Whitney,B.A.,Indebetouw,R.,Wood,K.,&Denzmore,P.2006,ApJS,167,256Sargent,A.,1977,ApJ,218,736Werner,M.,etal.,2004,ApJS,154,1
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Wolk,S.,etal.,2015,AJ,150,145Wilking,B.,etal.,2001,ApJ,551,357Witham,A.,etal.,2008,MNRAS,384,1277
