Messier 35 (NGC2168) DANCe I. Membership, proper motions and multi-wavelength photometry

3.3 MB·English

by  H. Bouy

Astronomy&Astrophysicsmanuscriptno.dance_m35 (cid:13)cESO2015
January20,2015
Messier 35 (NGC 2168) DANCe
I. Membership, proper motions and multi-wavelength photometry
H.Bouy1,E.Bertin2,D.Barrado1,L.M.Sarro3,J.Olivares3,4,5,E.Moraux4,5,J.Bouvier4,5,J.-C.Cuillandre6,Á.
Ribas1,7,8,andY.Beletsky9
1 Centro de Astrobiología, depto de Astroísica, INTA-CSIC, PO BOX 78, E-28691, ESAC Campus, Villanueva de la Cañada,
Madrid,Spain
e-mail:[email protected]
2 Institutd’AstrophysiquedeParis,CNRSUMR7095andUPMC,98bisbdArago,F-75014Paris,France
5
1
3 Dpt.deInteligenciaArtificial,UNED,JuandelRosal,16,28040Madrid,Spain
0
2
4 Univ.GrenobleAlpes,IPAG,F-38000Grenoble,France

n 5 CNRS,IPAG,F-38000Grenoble,France
a 6 Canada-France-HawaiiTelescopeCorporation,65-1238MamalahoaHighway,Kamuela,HI96743,USA
J

9 7 EuropeanSpaceAstronomyCentre(ESA),P.O.Box,78,28691VillanuevadelaCañada,Madrid,Spain
1
8 ISDEFE-ESAC,P.O.Box,78,28691VillanuevadelaCañada,Madrid,Spain

]
R 9 LasCampanasObservatory,CarnegieInstitutionofWashington,ColinaelPino,601Casilla,LaSerena,Chile
S
.
h Received;accepted18/01/2015
p
-
o ABSTRACT
r
t
s Context.Messier35(NGC2168)isanimportantyoungnearbycluster.Itsage,richnessandrelativeproximitymakeitaprivileged
a targetforstellarevolutionstudies.TheKeplerK2missionrecentlyobserveditandprovidedhighaccuracyphotometrictimeseries
[ ofalargenumberofsourcesinthisareaofthesky.Identifyingthecluster’smembersisthereforeofhighimportancetooptimizethe

interpretationandanalysisoftheKeplerK2data.
1
Aims.Weaimatidentifyingthecluster’smembersbyderivingmembershipprobabilitiesforthesourceswithin1◦ ofthecluster’s
v
center,goingfurtherawaythanequivalentpreviousstudies.
6
Methods. We measure accurate proper motions and multi-wavelength (optical and near-infrared) photometry using ground based
1
archivalimagesofthecluster.Weusethesemeasurementstocomputemembershipprobabilities.Thelistofcandidatemembersfrom
4
BarradoyNavascuésetal.(2001)isusedastrainingsettoidentifythecluster’slocusinamulti-dimensionalspacemadeofproper
4
motions,luminositiesandcolors.
0
Results.Thefinalcatalogincludes338892sourceswithmulti-wavelengthphotometry.Approximatelyhalf(194452)weredetected
.
1 atmorethantwoepochsandwemeasuredtheirpropermotionandusedittoderivemembershipprobability.Atotalof4349candidate
0 memberswithmembershipprobabilitiesgreaterthan50%arefoundinthissampleintheluminosityrangebetween10and22mag.
5 Theslowpropermotionoftheclusterandtheoverlapofitssequencewiththefieldandbackgroundsequencesinalmostallcolor-
1 magnitude and color-color diagrams complicate the analysis and the contamination level is expected to be significant. Our study
: neverthelessprovidesacoherentandquantitativemembershipanalysisofMessier35basedonalargefractionofthebestground-
v
baseddatasetsobtainedoverthepast18years.Assuch,itrepresentsavaluableinputforfollow-upstudiesusinginparticularthe
i
X KeplerK2photometrictimeseries.
r Keywords. Propermotions,Stars:kinematicsanddynamics,Galaxy:openclustersandassociations:individual:NGC2168
a
1. Introduction masses,perhapsindicatingdifferencesintheInitialMassFunc-
tions(IMF).Itisclearthatasignificantimprovementinthecom-
Different galactic environments, it is assumed, produce distinct pletenessofthecensusofdifferentassociationsprovidekeyin-
formationtounderstandstarformationandevolution.
populationsduringthestarformationepisodes.Fromveryloose
and young associations such as Taurus-Auriga, doomed to be Inthiscontext,theopenclusterMessier35(NGC2168,here-
dispersedverysooninthegalacticgravitationalwell,tothevery afterM35)isveryinterestinginseveralaspects.Firstbecauseit
oldhalopopulationinmassiveglobularclusters,thereisalarge is a quasi-twin of the Pleiades cluster, with a similar age (Vi-
gamut in ages, compactness, metallicity, internal dynamics, to- dal1973)butadifferentmetallicity.Second,theKeplerK2mis-
tal mass, spatial distribution and distribution of the individual sion(Howelletal.2014)hasjustprovidedexquisitephotometric
Articlenumber,page1of6
A&Aproofs:manuscriptno.dance_m35
time series, so that a detailed distribution of the rotational pe-
riods for different masses will be available (e.g Meibom et al.
2009).Moreover,M35isnotsocrowdedthatconfusionisama-
jor problem and its size (about 1 sq. deg) is very suitable for
follow-upmulti-objectspectroscopy(Barradoetal.2001a).
Several studies have provided estimates of other key clus-
terparameterssuchasitsage,itscensusanditsmetallicity.Ta-
ble 1 gives an overview of the cluster’s properties found in the
literature in the past fifteen years. However, there is no a clear
consensus for most of them. Sung & Bessell (1999) derived a
distance modulus of (m− M) = 9.60±0.10 corresponding to
0
832 pc, a reddening of E(B−V) = 0.255±0.024 mag and an
ageof200+200Myr.Kaliraietal.(2003)pushedtheclusteralit-
−100
tlebitfurther,to912+70 pcandderivedanisochronefittingage
−65
of 180 Myr. More recently, McNamara et al. (2011) obtained a
distanceof732±145pcfromtheinternalpropermotions.This
dynamical distance and the radial velocity dispersion obtained
byGelleretal.(2010)implyanageof133Myr,accordingtothe
Fig. 1. Estimated error on the proper motion as a function of i-band
sameauthors.Anagedeterminationbasedonacompletelydif- magnitude. The color scale represents the maximum time difference
ferent technique –gyrochronology– was performed by Meibom
usedforeachmeasurement.ThepredictionforGaiaisover-plottedfor
et al. (2009), yielding a value between 134 Myr and 161 Myr. comparison.
Reimers&Koester(1988),byusingthewhitedwarfcoolingage,
derivedanageintherange70-100Myr,whereasBarrado(2001),
with the same technique, estimated 180 Myr. The rotation pat-
tern suggests an age slightly older than the Pleiades (175 Myr ofeachCCD,flat-fieldcorrection,badpixelmasking,CCD-to-
compared to 125 Myr). The same conclusion is reached when CCD gain harmonization in the case of multi-chip instruments,
the lithium abundances are compared, since the lithium disper- fringing correction (when needed for the reddest filters), de-
sion, which is itself related to rotation for a given stellar mass, stripping, background subtraction and non-linearity correction
is no longer obvious for M35 (Barrado et al. 2001a) while it inthecaseofnear-infrareddetectors.
is very significant in the case of the Pleiades (see, for instance
Aperture, PSF and model photometry were extracted from
Soderblometal.1993). the individual images using SExtractor (Bertin & Arnouts
Regarding chemical composition, Steinhauer & Deliyannis 1996) and PSFEx (Bertin 2011). The individual catalogs were
(2004)quotedanunpublishedworkwithametallicity[Fe/H]=
thenregisteredandalignedonthesamephotometricscaleusing
−0.143±0.014,verysimilartothevalueobtainedbyourgroup Scamp(Bertin2006).
([Fe/H]=−0.21±0.10)usinghighspectralresolutiondataand
spectralsynthesis,(Barradoetal.2001a). The photometric zero-points were derived using standard
The cluster is also relatively massive: Leonard & Merritt fieldsobtainedthesamenightwheneveravailable,orall-skycat-
(1989) derived a central total mass in the range 1600-3200 aloguessuchas2MASS(Skrutskieetal.2006)inJ,HandKs,
M using dynamical models. Our own estimate, for the cen- SDSSing,r,i,zandIPHAS(Drewetal.2005)inHα.Thezero-
(cid:12)
tralof27.5×27.5squarearcmin,is∼ 1600M ,whichallowsa pointrmsweretypicallyintherangebetween0.02and0.12mag,
(cid:12)
exquisitedeterminationofacompletestellarmassfunction(Bar- and were added quadratically to the measurement uncertainty.
rado et al. 2001b, so far the deepest for M35) which is totally No attempt was made to calibrate the non-standard VR filters
compatible with the IMF of a much younger and un-evolved used with the Mosaic and SuprimeCam cameras and the He I
cluster such as Collinder 69 (Barrado et al. 2005; Bayo et al. narrowbandfilterobtainedwiththeWFC.
2011), and suggests that M35 includes several tens of potential
Proper motions for all the sources were computed using
substellarmembers.
the method described in Bouy et al. (2013). The final residu-
Thegoalofthispaperistocompletethecensusreachingwell
alsontheastrometricsolutionshowadispersionoftheorderof
inside the substellar domain and including the cluster outskirts
11∼12 mas. Figure 1 shows the estimated error on the proper
uptoaradiusof1◦,providingmulti-epoch,multi-bandphotom-
motionasafunctionofi-bandapparentmagnitude.Wenotethat
etryfrompublicarchivesandfromourownrecentobservations.
thepropermotionmeasurementsarenottiedtoanabsoluterefer-
encesystemsuchastheICRS(InternationalCelestialReference
2. Datasets System).TheyareneverthelessexpectedtobeclosetotheICRS
since extragalactic sources and background stars largely domi-
WesearchedtheCFHT,NOAO,Subaru,Kiso,SDSS(DR9, Ahn
natethesampleanddisplayverylittlemotionwithrespecttothe
etal.2012)andINGpublicarchivesforwidefieldimagesofthe
ICRS.
cluster. Table 2 gives an overview of the dataset found in these
archivesandinourownprivatearchives. A final master catalog of all sources (338892 in total)
Ineachcase,therawdataandassociatedcalibrationframes was then produced including the measured photometry in the
were downloaded. The individual raw images were processed grizJHKs filters. A total of 194452 sources (approximately
using an updated version of Alambic (Vandame 2002), a soft- half) were detected at more than two epochs and their proper
ware suite developed and optimized for the processing of large motionarealsoincluded.Sincethemaingoalofthesurveyfo-
multi-CCDimagers,andadaptedfortheinstrumentsusedhere. cusesonthestudyofM35,onlyobjectswith|µ cosδ|≤100mas
α
Alambic includes standard processing procedures such as over- yr−1 and |µ | ≤100 mas yr−1 were considered for the member-
δ
scan,biasanddarksubtractionforeachindividualreadoutports shipanalysis.
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H.Bouy etal.:Messier35(NGC2168)DANCe
Table1.OverviewofpreviousstudiesofM35
Reference Distance Age E(B−V) [Fe/H]
(pc) (Myr) (mag)
Reimers&Koester(1988) 70–100
Sung&Bessell(1999) 832±39 200+200 0.255±0.024
−100
Barrado(2001) 180
Barradoetal.(2001a) >125 −0.21±0.10
Kaliraietal.(2003) 912+70 180
−65
Steinhauer&Deliyannis(2004) −0.143±0.014
Meibometal.(2009) 134–161
Gelleretal.(2010) 133
McNamaraetal.(2011) 732±145
Table2.Instrumentsusedinthisstudy
Observatory Instrument Filters Platescale Chiplayout Chipsize Fieldofview Epoch(s) Ref.
[pixel−1]
CFHT UH8K R,I 0(cid:48).(cid:48)205 4×2 2k×4k 29(cid:48)×29(cid:48) 1996 1
CFHT CFHT12K B,V,R,I,z 0(cid:48).(cid:48)201 6×2 2k×4k 42(cid:48)×28(cid:48) 1999,2000,2001,2002 2
CFHT MegaCam g,r 0(cid:48).(cid:48)187 4×9 2k×4k 1◦×1◦ 2003,2005,2011 3
CFHT WIRCam H2 0(cid:48).(cid:48)304 2×2 2k×2k 20(cid:48)×20(cid:48) 2008,2009,2010,2011 4
Subaru Suprime-Cam VR-Broad 0(cid:48).(cid:48)200 5×2 2k×4k 34(cid:48)×27(cid:48) 2005 5
INT WFC g,Hα,HeI,i,I,r,U,V 0(cid:48).(cid:48)333 3×1+1 2k×4k 34(cid:48)×34(cid:48) 2000,2002,2003,2005,2008,2009,2010 6
KPNO(Mayall) NEWFIRM J,H,Ks 0(cid:48).(cid:48)400 2×2 2k×2k 28(cid:48)×28(cid:48) 2008 7
KPNO(Mayall) MOSAIC1 VR-broad 0(cid:48).(cid:48)26 4×2 2k×4k 36(cid:48)×36(cid:48) 2006,2009,2010,2011,2012 8
KISO 2KCCD B,V,R,I 1(cid:48).(cid:48)50 1×1 2k×2k 50(cid:48)×50(cid:48) 2002,2003 9
SDSSDR9 SDSScamera u,g,r,i,z 0(cid:48).(cid:48)396 6×5 2k×2k 3◦ 2006
References:(1)Metzgeretal.(1995),(2)Cuillandreetal.(2000),(3)Bouladeetal.(2003),(4)Pugetetal.(2004),(5)Miyazakietal.(2002),(6)Ives(1998),(7)Autryetal.(2003),(8)
Wolfeetal.(2000),(9)Itohetal.(2001),(10)Ahnetal.(2012)
3. Membership inconsistent with the cluster’s sequence. Their high probabil-
ity is due to their proximity to the isochrone in all other color-
We use the method described in Sarro et al. (2014) to derive magnitude and color-color diagrams as well as to the cluster’s
membershipprobabilitiesofallthesources.Briefly,themethod locus in the proper motion diagram. These sources – probably
uses a training set – in this case the sample of candidate mem- sufferingfrominaccuratephotometryinoneofthesebands–il-
bersfromBarradoyNavascuésetal.(2001)–toidentifythefea- lustrate the robustness of the selection method based on a high
turesthatmostefficientlyseparatethecluster’spopulationfrom dimensionalspace.
thefieldandbackgroundpopulationamongallcombinationsof
Table ?? gives the astrometry, photometry and membership
propermotion, luminositiesandcolorsavailable. Inthecase of
probability for the 338892 unique sources detected in the cor-
M35, the best set was found to include the proper motions, the
responding area. Note that only the sources with a proper mo-
z,H,Ksluminositiesandthe(r−z),(r−i)and(J−H)colors.
tion measurement have a membership probability (194452 in
Oncethebestsetofcolors,luminositiesandpropermotionisse-
total),astheavailabilityofapropermotionmeasurementwasa
lected,amodelofthecluster’slocusdefinedbythetrainingsetis
necessaryconditioninourmembershipanalysis.Usingsources
fitted in the corresponding multi-dimensional space. A mixture
with membership probability greater or equal to 0.9, we derive
ofGaussiansisusedforthepropermotiondiagramandprinci-
amedianpropermotionfortheclusterof(µ cosδ,µ )=(1.99,-
palcurvesforthecluster’ssequenceinallcolor-magnitudeand α δ
0.23)±(0.82,0.71)masyr−1,wheretheuncertaintiescorrespond
color-color diagrams. Membership probabilities are then com-
tothescaledmedianabsolutedeviation.
puted using this first model. The highest probability members
are selected as new training set, and the models and the mem- Figure4showsthemembershipdistributionandcumulative
bershipprobabilitiesarerecomputeduntiltheyconverge. distribution(computedfromlargetosmall)forallthesourcesin
thecatalog.Thevastmajorityofthesourceshasamembership
This method was originally developed and optimized for
probabilityof≈0.0.Amonotonouslydecreasingdistributionfills
clusters like the Pleiades, i.e clusters with a relatively large
theprobabilityrangebetween0and1.0,astheresultofthelose
propermotionandphotometricsequenceclearlyseparatedfrom
constraintsonthephotometricandastrometricpropertiesofthe
the field and background sequences in many color-magnitude
cluster.
diagrams. Unfortunately M35 is a worst-case scenario for the
method. Its proper motion is relatively small and its sequence NGC2158isanintermediateage(1∼2Gyr)clusteratadis-
largely overlaps with the field and background sequence in al- tance of ≈3600 pc (Carraro et al. 2002) located at a projected
mostallcolor-magnitudeandcolor-colordiagrams.Tolimitthe distance of only 25(cid:48) from M35. It is therefore included in the
contamination and enhance the contrast between cluster mem- areacoveredbythepresentstudyandpossiblycontaminatesthe
bers and field and background sources, we chose to restrict the membershipanalysis.Toestimatethelevelofcontaminationdue
analysis to a radius of 1◦ around the cluster’s center located toNGC2158members,weselectallthesourceslocatedwithin
atα=06h08m54.0s,andδ=+24◦20(cid:48)00(cid:48)(cid:48)(J2000).Figure2shows 3(cid:48) of its center. Given the distance and projected density pro-
theirspatialdistribution.Itshowsthatthenorth-westernpartof fileofNGC2158,thesesourcesareexpectedtobeintheirvast
the survey was shallower than the rest of the survey, as fewer majority members of NGC 2158. Figure 5 shows the sequence
members were selected. It also shows that a number of high formed by these sources in various color-magnitude diagrams
probability members have (r − i) or (i − Ks) color apparently madeofcolorsandluminositiesusedforthemembershipanal-
Articlenumber,page3of6
A&Aproofs:manuscriptno.dance_m35
Fig.3.Colormagnitudeandpropermotiondiagramsofthe194452sourcesofthesampledetectedatmorethantwoepochs.Left:r vsr−i.
Middle:ivsi−Ks.Right:propermotiondiagram.Sourceswithamembershipprobabilitygreaterorequalto0.5arerepresentedinthetoppanels
withacolorscaleproportionaltotheirprobability.Therestofthesourcesisrepresentedinthebottompanels.
Fig.4.Distribution(blue,leftscale)andcumulativedistribution(red,
computedfromlargetosmallvalues,rightscale)ofmembershipprob-
Fig.2.Spatialdistributionofsourcesusedastrainingset(greensquares,
abilitiesforthe194452sourcesofthesample
from BarradoyNavascuésetal.2001)andofthe4349sourcesofthe
finalsamplewithmembershipprobabilitygreaterthan0.5.Background
image:2MASSJ-band.
i (cid:46)17 mag. We find that only 27 sources with a probability
of membership to M35 greater than 0.5 are located within 3(cid:48)
ysispresentedhere,andcomparesittothesequenceformedby of NGC 2158, and 53 within 5(cid:48). Given the projected size of
objects with a probability of membership to M35 greater than NGC2158core,littlecontaminationisexpectedbeyond5(cid:48),and
0.5accordingtoouranalysis.Thetwosequencesoverlapmostly thecontaminationbyNGC2158membersmustnotreachmore
at the bright end, and contamination must occur mostly above than1∼2%atmost.
Articlenumber,page4of6
H.Bouy etal.:Messier35(NGC2168)DANCe
Fig.5.Color-magnitudediagramsoftheM35highprobabilitymembers(≥0.5.reddots)andofallthesourceswithin3(cid:48) ofNGC2158center(blue
dots).
4. Conclusions publicallyavailablethroughtheIsaacNewtonGroup’sWideFieldCameraSur-
veyProgramme.TheIsaacNewtonTelescopeisoperatedontheislandofLa
Wehaveprocessedandanalyzedatotalof4867wide-fieldopti- PalmabytheIsaacNewtonGroupintheSpanishObservatoriodelRoquedelos
calandnear-infraredimagesofM35obtainedfromvariouspub- MuchachosoftheInstitutodeAstrofísicadeCanarias.Thisresearchusedthe
lic astronomical archives. The images cover 18 years of time facilitiesoftheCanadianAstronomyDataCentreoperatedbytheNationalRe-
searchCouncilofCanadawiththesupportoftheCanadianSpaceAgency.This
baseline and typically reach a depth of 21≈22 mag in the op-
researchdrawsupondatadistributedbytheNOAOScienceArchive.NOAOis
tical and ≈19 mag in the near-infrared, while saturation arises operatedbytheAssociationofUniversitiesforResearchinAstronomy(AURA)
around 12∼13 mag at the bright end. This dataset allows us to undercooperativeagreementwiththeNationalScienceFoundation.Thispubli-
derivemulti-wavelengthphotometryfromtheopticaltothenear- cationmakesuseofdataproductsfromtheTwoMicronAllSkySurvey,whichis
ajointprojectoftheUniversityofMassachusettsandtheInfraredProcessingand
infrared for 338892 sources, and proper motions for 194452 AnalysisCenter/CaliforniaInstituteofTechnology,fundedbytheNationalAero-
ofthem.Weusethesemeasurementstoderivethemembership nautics and Space Administration and the National Science Foundation. This
probabilityofallthesourceswithapropermotionmeasurement. workisbasedinpartondataobtainedaspartoftheUKIRTInfraredDeepSky
Weobtain: Survey.ThisresearchhasmadeuseoftheVizieRandAladinimagesandcata-
logueaccesstoolsandoftheSIMBADdatabase,operatedatCDS,Strasbourg,
France.ThisresearchmadeuseofdatafromtheSDSSsurvey.Fundingforthe
– 4349candidatememberswithprobabilitygreaterthan50%
creationanddistributionoftheSDSSArchivehasbeenprovidedbytheAlfred
– 1726candidatememberswithprobabilitygreaterthan75% P.SloanFoundation,theParticipatingInstitutions,theNationalAeronauticsand
– 305candidatememberswithprobabilitygreaterthan95% SpaceAdministration,theNationalScienceFoundation,theU.S.Departmentof
Energy,theJapaneseMonbukagakusho,andtheMaxPlanckSociety.TheSDSS
Websiteishttp://www.sdss.org/.TheParticipatingInstitutionsareTheUniver-
ThesenumbersareconsistentwiththecensuspresentedinBar-
sityofChicago,Fermilab,theInstituteforAdvancedStudy,theJapanParticipa-
radoyNavascuésetal.(2001)overasmallerarea.Contamina- tionGroup,TheJohnsHopkinsUniversity,theMax-Planck-InstituteforAstron-
tionisexpectedtobesignificantasthelocusoftheclusterinthe omy(MPIA),theMax-Planck-InstituteforAstrophysics(MPA),NewMexico
propermotion,color-magnitudeandcolor-colordiagramsover- StateUniversity,PrincetonUniversity,theUnitedStatesNavalObservatory,and
theUniversityofWashington.BasedondatacollectedatSubaruTelescopeand
lapslargelywiththefieldandbackgroundlocus.Thisnewstudy
Kisoobservatory(UniversityofTokyo)andobtainedfromtheSMOKA,which
nevertheless provides a coherent and quantitative membership isoperatedbytheAstronomyDataCenter,NationalAstronomicalObservatory
analysis of M35 based on a large fraction of the best ground- ofJapan.
baseddatasetsobtainedoverthepast18years.
Acknowledgements. H. Bouy is funded by the the Ramón y Cajal fellowship
program number RYC-2009-04497. This research has been funded by Span- References
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