NASA Technical Reports Server (NTRS) 20130014464: New Brown Dwarf Discs in Upper Scorpius Observed with WISE

2.1 MB·English

by  NASA Technical Reports Server (NTRS)

MNRAS429,903–914(2013) doi:10.1093/mnras/sts386
New brown dwarf discs in Upper Scorpius observed with WISE
P. Dawson,1‹ A. Scholz,1 T. P. Ray,1 K. A. Marsh,2 K. Wood,3 A. Natta,1,4 D. Padgett5
and M. E. Ressler6
1SchoolofCosmicPhysics,DublinInstituteforAdvancedStudies,31FitzwilliamPlace,Dublin2,Ireland
2SchoolofPhysicsandAstronomy,CardiffUniversity,CardiffCF243AA
3SchoolofPhysicsandAstronomy,UniversityofStAndrews,NorthHaugh,StAndrewsKY169SS
4INAF–OsservatorioAstrofisicodiArcetri,LargoE.Fermi5,I-50125Firenze,Italy
5GoddardSpaceFlightCenter,Greenbelt,MD20771,USA
6JetPropulsionLaboratory,CaliforniaInstituteofTechnology,4800OakGroveDrive,Pasadena,CA91109,USA
Accepted2012November8.Received2012October12 D
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ABSTRACT e
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We present a census of the disc population for UKIDSS selected brown dwarfs in the 5– fro
m
10MyroldUpperScorpiusOBassociation.For116objectsoriginallyidentifiedinUKIDSS, h
the majority of them not studied in previous publications, we obtain photometry from the ttp
Wide-FieldInfraredSurveyExplorerdatabase.Theresultingcolour–magnitudeandcolour– ://m
n
colour plots clearly show two separate populations of objects, interpreted as brown dwarfs ras
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withdiscs(classII)andwithoutdiscs(classIII).Weidentify27classIIbrowndwarfs,14of xfo
themnotpreviouslyknown.Thisdiscfraction(27outof116,or23%)amongbrowndwarfs rd
jo
u
wasfoundtobesimilartoresultsforK/MstarsinUpperScorpius,suggestingthatthelifetimes rn
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ofdiscsareindependentofthemassofthecentralobjectforlow-massstarsandbrowndwarfs. ls
.o
5outof27discs(19percent)lackexcessat3.4and4.6µmandarepotentialtransitiondiscs rg
a/
(i.e. are in transition from class II to class III). The transition disc fraction is comparable to t N
A
low-massstars.Weestimatethatthetime-scaleforatypicaltransitionfromclassIItoclassIII S
A
islessthan0.4Myrforbrowndwarfs.Theseresultssuggestthattheevolutionofbrowndwarf G
o
discsmirrorsthebehaviourofdiscsaroundlow-massstars,withdisclifetimesoftheorderof d
d
a
5–10Myrandadiscclearingtime-scalesignificantlyshorterthan1Myr. rd
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Key words: techniques: photometric–open clusters and associations: individual: Upper ac
e
Scorpius–infrared:stars. Flig
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1 INTRODUCTION OfoBrmaisnsgocreiagtiioonnw(UithpSacsoubinstathnetiaflolnluomwibnegr)o,fthberoowldnedstwnaerfasr.bUypsStacro- ril 3, 2
Browndwarfs–substellarobjectswithmassesbelowtheHydrogen is often assumed to have an age of 5Myr (Preibisch et al. 2002) 0
1
3
burninglimitof0.08M(cid:2)–areidealtotestthemassdependenceof but recently Pecaut, Mamajek & Bubar (2012) have derived an
criticalparametersinstellarevolution.Oneexampleforsuchapa- older age of 10Myr for this region. In UpSco, Carpenter et al.
rameteristhelifetimeofcircumstellardiscs,whichisanimportant (2006) derived a disc frequency of <8percent for F and G stars
constraintforthecore-accretionscenariosforplanetformation.The and19±4percentforK0–M5stars(with1σ binomialconfidence
disclifetimeisaffectedbyanumberofphysicalprocesses,e.g.disc intervals).Thebrowndwarfsinthisregionexhibitadiscfraction
ionization by the central object and cosmic rays, accretion, grain of37±9percent,basedonanexaminationof35objects(Scholz
growth(e.g.Dullemondetal.2007).Ourunderstandingoftherela- et al. 2007). Thus, the Spitzer data tentatively show that the disc
tiveimportanceoftheseprocessesandhowtheychangewithobject fractionsinUpScoincreasemonotonicallywithdecreasingobject
massisstillincomplete,i.e.observationalguidanceisimportantto massforearlyF-tolateM-typeobjects.Thiswouldimplyamass
advancethetheory. dependenceinthediscevolution,resultinginlong-liveddiscsinthe
Theclearmajorityoflow-massstarslosetheirdiscwithinless substellarregime.
than5Myr(Haisch,Lada&Lada2001;Jayawardhanaetal.2006). Sofar,thebrowndwarfdiscfrequencyinUpScoisaffectedby
MaybethebesttestforthelongevityofdiscsistheUpperScorpius lownumberstatistics.Herewesetouttotestpreviousfindingsbased
onamuchenlargednumberofbrowndwarfsinUpSco,identified
fromUKIDSS.Toidentifytheobjectsinoursamplethathaveadisc
(cid:2) (class II objects) and those that do not (class III objects), we use
E-mail:[email protected]
(cid:3)C 2012TheAuthors
PublishedbyOxfordUniversityPressonbehalfoftheRoyalAstronomicalSociety
904 P.Dawsonetal.
Figure1. (Z−J,Z)and(W1−W2,Z)colour–magnitudediagramsfor116outof119browndwarfsidentifiedinUpScoforwhichWISEdatawereavailable.
TheclassIIobjectsaremarkedinredintheonlineversionofthispaper.The5MyrDUSTYmodel(Chabrieretal.2000)isochronesarealsoshownwith D
o
massdecreasingfrom0.09(top)to0.01M(cid:2)(bottom).The0.05M(cid:2)positionsontheisochronesareindicated.Inthe(Z−J,Z)diagramalltheobjectsare w
n
groupedclosetotheisochroneandnoneshowanysignificantcolourexcess.However,twodistinctpopulationsofobjectsareclearlyvisibleinthe(W1−W2,Z) lo
a
diagram,oneclosetotheisochroneandoneshowinganexcessinW1−W2.The11objectsringedhavebrightunambiguoussignalsinW4(22µm),diagnostic de
d
ofthepresenceofadisc(seethetext;Section4.1.4).ThefourobjectsmarkedwithacrosshavesignificantvariationsintheirUKIRTand2MASSJorH fro
magnitudes,acharacteristicassociatedwithaccretioneventsorvariableextinction(alsoseethetext;Section4.2). m
h
ttp
datafromtheWide-FieldInfraredSurveyExplorer(WISE)(Wright sonetal.2011,alsoseeAppendixAthispaper).Consequently,it ://m
et al. 2010). As will be shown, with improved statistics we find canbeinferredthatthe(Z−J,Z)valueforanyoftheobjectsis n
ra
a disc fraction for brown dwarfs that is consistent with the value photospheric in origin with negligible contribution from any cir- s.o
publishedforlow-massstarsinthisregion. cumsubstellardisc.Thus,themethodofselectingthese119objects xfo
isunbiasedwithrespecttothepresenceofcircumsubstellardiscs. rd
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As pointed out above, the 26 objects in our sample with pub- u
rn
2 TARGETS lishedspectrahavebeenconfirmedtobeverylow-massmembers als
of UpSco. In addition, we have recently obtained spectra for 25 .o
rg
Dawson,Scholz&Ray(2011)identified19newbrowndwarfcan- furtherobjectsfromthissample;allofthemareconfirmedasvery a/
didatesinthesouthofUpScoviaaphotometricandpropermotion low mass members of UpSco as well (Dawson et al., in prepara- t N
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analysisofUKIDSSdata.Thelevelofcontaminationfromback- tion).Althoughthespectroscopicfollow-upisnotyetcompletefor S
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groundstarsinthesamplewasshowntobenegligible.Usingthe oursample,the100percentsuccessrateforalmosthalfthesam- G
samemethodinthenorthofUpScoafurther49objectspreviously ple indicates that our selection method based on photometry and od
d
identifiedbyLodieu,Hambly&Jameson(2006)andLodieuetal. propermotiongeneratesaclean,unbiasedsamplewithnegligible ard
(2007) as brown dwarf candidates were recovered. Spectra have contaminationbybackgroundobjects(≤2percent). S
p
been taken of 26 of these 49 objects (Martin, Delfosse & Guieu ac
e
2004;Lodieuetal.2006,2008;Slesnick,Carpenter&Hillenbrand F
2006;Lodieu,Dobbie&Hambly2011)andall26havebeencon- 3 WISE DATA ligh
fistremlleadraansdbrsouwbsntedlwlaarrofsb.jTechtissipnroUvpidSecsoa.sDaamwpsloenofet6a8lv.e(2ry01lo1w)-dmetaesrs- FTohre1r1e6moafinthineg11th9retaergweetsredinsocutslsisetdedabionvethweeWoIbStEaindeadtaWbIaSsEe.daFtoar. t Ctr on
minedthatthe68objectsrangedinmassfrom0.01to0.09M(cid:2)by the116,the2MASSidentifierlistedintheWISEdatabaseagrees Ap
comparingtheirobservedZmagnitudeswiththeoreticalZmagni- withtheonefromUKIDSS.Inaddition,allobjectswerevisually ril 3
tudesfromtheDUSTYmodelsfor5Myroldobjects. examinedintheWISEimagesandintheUKIDSSimages.Itwas , 2
0
Dawsonetal.(2011)usedtheEighthDataReleasefromUKIDSS foundthatforthe116objectsanalysedhere,theidentificationof 13
toidentifythenewbrowndwarfs.Sincethen,UKIDSShasissued theUKIDSSsourcewiththeWISEsourceatthesamepositionis
a Ninth Data Release which covers a substantially larger area in unambiguous (for the three excluded targets this is not the case).
UpSco. Using the same method as in Dawson et al. (2011), we Furthermore,sinceourtargetfieldsaresparselypopulatedandwell
haveidentifiedafurther51objectsinthesamemassrangetoadd above the Galactic plane (latitude 10–30 deg), the likelihood of
to the sample. The details of this extended survey are given in accidentalcontaminationbyotherobjectsisverylow.
AppendixA.Theadditionofthesenewobjectsincreasesthesize WISE surveyed the whole sky in four mid-infrared wavebands
ofthehomogeneoussampleofobjectsuniformlyselectedviatheir simultaneously,usingpassbandswitheffectivewavelengthsof3.4
colour and proper motion characteristics to 119. Although some (W1),4.6(W2),12(W3)and22µm(W4).Weusedtheresultsof
objectsinoursamplemaybeslightlyabovethesubstellarthreshold, profile-fitting photometry from the All Sky Data Release, further
wewillrefertoourtargetsas‘browndwarfs’throughoutthispaper, details of which can be found in Cutri et al. (2012).1 Among the
forsimplicity. 116 objects are 2 that were previouslyexamined by Scholz et al.
All119objectslieclosetothe5MyrDUSTYmodelisochrones (2007)andconfirmedtohavediscs.
ofChabrieretal.(2000)ina(Z−J,Z)UKIDSSpassbandscolour–
magnitudediagram,asshowninFig.1,i.e.noneofthemexhibitany
substantialexcessatthesenear-infraredwavelengths.Theobjects 1For more details of the WISE All Sky Data Release also see
arealsogenerallyfreefromreddeningcausedbyextinction(Daw- http://wise2.ipac.caltech.edu/docs/release/allsky/expsup/.
NewbrowndwarfdiscsinUpperScorpius 905
4 COLOUR ANALYSIS 4.1.2 W1−W2:ComparisonwithScholzetal.(2007)
ThefiveUnitedKingdomInfraredTelescope(UKIRT)passbands; Totestthatthemethodoutlinedabovewassuccessfullydiscriminat-
Z,Y,J,HandKhaverespectivewavelengthsof0.88,1.03,1.25, ingbetweenclassIIandclassIIIobjects,itwasalsoappliedtothe
1.63 and 2.20µm. Similar J, H and K passbands are also used 35objectsinUpScoexaminedbyScholzetal.(2007).Thatstudy
in 2MASS. As noted above, the four WISE passbands, W1, W2, usedaSpitzersurveycombiningspectroscopyfrom8to12µmand
W3andW4,havelongerwavelengthsof3.4,4.6,12and22µm,re- photometryat24µm.As33ofthe35objectslieoutsidethearea
spectively.Differentcolour–colourandcolour–magnitudediagrams covered by UKIDSS there is no Z or Y passband data available
usingcombinationsofallninepassbandswereexamined.The(Z− forthem.However,theyarerecordedintheJ,H andKpassbands
J, Z ) andW( 1–W2,Z) colour–magnitude diagrams are shown in of2MASS.The35objectswereplottedina(W1−W2,J)colour–
Fig.1.Theoreticalisochronesfor5Myroldsubstellarobjectsare magnitudediagram(shownintheright-handpanelofFig.2)using
alsoshownoverplottedonthediagrams.Theseisochronesarebased datafrom2MASS.The116objectsfromthisworkwerealsoplotted
ontheDUSTYmodelsderivedbyChabrieretal.(2000)andob- ina(W1−W2,J)colour–magnitudediagram(shownintheleft-hand
tainedfrombothBaraffeandAllard(privatecommunications).The panelofFig.2)forcomparison,usingdatafromtheUKIDSSJpass-
isochroneswerecomputedusingboththeUKIDSSandWISEfilter band.TwooftheobjectsfromScholzetal.(2007)lieinsidethearea
profiles. The (Z − J, Z) isochrone was used to assign masses to coveredbyUKIDSSandwererecoveredbyDawsonetal.(2011).
objectsbyDawsonetal.(2011).Theuppermostpointonthe5Myr The differences in their UKIDSS and 2MASS J magnitudes are D
o
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isochronecorrespondstoamassof0.09M(cid:2)whilethelowestpoint negligible(0.06maginbothcases). n
correspondstoamassof0.01M(cid:2). Ascanbeseenfromtheright-handpanelofFig.2,alltheobjects loa
d
withcircumsubstellardiscshavesufficientexcessinW1−W2(3.4– ed
4.6µm)tostandclearoftheobjectswithnodiscsclusteredalong fro
m
theisochrone.Afewoftheobjectswithdiscsexhibitalesser,but h
4.1 WISEdataforUpScobrowndwarfs stillsignificantcolourexcessinW1−W2(i.e.theyaremorethan2σ ttp
4.1.1 W1−W2(3.4–4.6µm) awayfromtheisochrone).Themethodsuccessfullydiscriminated ://mn
betweenthe13classIIand22classIIIobjectsinthissample. ra
Inthe(Z−J,Z)diagramalltheobjectsaregroupedclosetothe s.o
x
isochroneandnoneshowanysignificantcolourexcess,asdiscussed fo
rd
above.However,twodistinctpopulationsofobjectsareclearlyvis- 4.1.3 W3(12µm) jou
ible in the (W1−W2,Z) diagram, one close to the isochrone and rn
a
one showing an excess in W1−W2 (3.4–4.6µm). The population Colours that utilize the longer wavelength W 3 (12µm) passband ls
.o
with excess is best understood as objects harbouring dusty discs areoflimiteduseasonly39ofthe116objectshaveanS/N>5.0in rg
atwndotphoepreufloatrieonesmditotinngotthsehromwalupinfinrarthede draiadgiartaimons(tchlaatssutIiIl)iz.eTohneslye TWh3e.3B9yocbojnetcrtasstw,iatlhl1an16So/Nbje>ct5s.h0aivneWan3Sw/Nere>fu8r.t0heinreWxa1mainndeWdi2n. at NA/
UKIRTpassbands.OtherdiagramsthatcombinebothUKIRTand the(W1−W2,W3)colour–magnitudediagramshowninFig.3.They SA
WISEpassbandsdoshowthetwopopulations.Coloursthatusea areallamongthehighermassobjectsinthesample,asevidenced G
o
UKIRTandWISEW1(3.4µm)passbanddoshowthetwopopula- bythelackofobjectsaroundthelowerpartoftheisochrone.The dd
a
tionsbutnotasclearlyascoloursincorporatingW2(4.6µm).The population with the W1−W2 (3.4–4.6µm) colour excess is again rd
S
K−W2 colour inparticular discriminates between the twopopu- distinctfromthepopulationclosetotheisochroneasintheprevious pa
lationsalmostaswellastheW1−W2colour.TheW1−W2colour diagrams.TheninthbrightestobjectinW3nowstandsclearfrom ce F
was chosen as the primary diagnostic for distinguishing between thepopulationneartheisochrone.Whilethisobjectisnotobviously lig
classIIandclassIIIobjectsinthiswork(seeFigs1and2). partofthepopulationwithexcessinW1−W2seeninFigs1and ht C
tr o
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ril 3
, 2
0
1
3
Figure2. (W1−W2,J)colour–magnitudediagrams.The116browndwarfswithavailableWISEdataanalysedinthisworkareshownintheleft-handpanel
withsymbolsandisochroneasinFig.1.Theright-handpanelshowsthesamediagramfor35objectsinUpScoidentifiedinScholzetal.(2007).Objects
confirmedashavingdiscsinScholzetal.(2007)areshownasclosedtriangleswhilethosewithnodiscdetectedareshownasclosedcircles.Ascanbeseen,
theobjectsinthepopulationwithobviouscolourexcessallhavediscs.Afewobjectswithdiscsexhibitasmaller,butstillsignificantcolourexcess(i.e.they
aremorethan2σ awayfromtheisochrone).Objectswithnodisclieclosetotheisochrone.
906 P.Dawsonetal.
Table 1. Objects with photometric variability
>0.2maginJ,HorK.
Name (cid:4)J (cid:4)H (cid:4)K
2MASSJ15514709−2113234 0.84 0.59 0.25
2MASSJ15521088−2125372 0.24 0.11 0.03
2MASSJ15472282−2139141 0.38 0.25 0.21
2MASSJ16030235−2626163 0.17 0.30 0.11
4.1.5 (W1−W2,J−K)
The(W1−W2,J−K)colour–colourdiagraminFig.4wasexamined
to see if class II and class III objects could be clearly separated.
ApartfromthetwoobjectswhicharebrightinW4andhavelarge
differencesintheirUKIDSSand2MASSJmagnitudes,noneofthe
Figure3. (W1−W2,W3)colour–magnitudediagramfor39ofthe116ob- objectsshowanysignificantexcessinJ−K.Thisservestoconfirm
D
jectswithanS/N>5.0inW3(12µm).Symbolsandisochronearethesame previousfindings(Natta&Testi2001;Nattaetal.2002)thatthe o
w
asinFig.1.The39objectsareallamongthehighermassobjectsinthe efficacyofusingJ−Kexcessasadiagnosticforthepresenceof nlo
sample,asevidencedbythelackofobjectsaroundthelowerpartofthe discsaroundverylowmassstarsandbrowndwarfsisverylimited. ad
isochrone. ed
fro
b2a,siitsiosfmitosreextcheasnsi2nσWa1w−aWy2fraonmditthsebirsiogchhtnroesnse.inOWn3t,hietacpopmebairnsetdo 4.2 Variableobjects httpm
haveadiscandsoisincludedinthegroupofclassIIobjects.This A comparison was also made of the UKIDSS and 2MASS pho- ://m
oobfjSecchtoislzoenteaol.f(t2h0e0t7w)owohbojencotstectohmatmitohnatsoabboitnhatrhyiscostmudpyanainodntahtaat taotmdeiftfreyrefonrteeapcohchosbjseecvt.erUaKl IyDeaSrSsaanpdar2tM–A2SMSAdSaStabweetwreegeanth1e9r9ed7 nras.o
and2001(Skrutskieetal.2006)andUKIDSSfrom2005onwards x
separationof12au. fo
(Lawrenceetal.2007).Ofthe116objects,112showedavariationof rd
lessthan0.2maginJ,HandK.Theremainingfour,whicharelisted jou
4.1.4 W4(22µm) inTable1(andmarkedwithcrossesinFigs1,2,3and4),showed rnals
variationsofgreaterthan0.2maginJ,HorK.Suchvariationsin .o
TheobjectsalsohadtheirdetectionintheW4(22µm)WISEpass- rg
bandexamined.Photosphericemissionfrombrowndwarfsisneg- Jcrheativoen.bSeecnhoilnzteertparle.t(e2d0b0y9)Sfcuhrtohlezrentoatle.t(h2a0t0c9o)oalsspsoigtsn(actuormespaorfabacle- at N/
ligible by comparison with emission from a disc at wavelengths tosunspots)areexpectedtoproducevariationsof<0.15maginJ AS
longerthan20µm(Scholzetal.2007).Therefore,anyobjectwith and<0.1maginKwhilelarge-scalephotometricvariabilitywith A G
abrightunambiguoussignalinW4showsclearevidenceofthepres- amplitudes declining towards longer wavelengths – as displayed od
(e3n.c4e–4o.f6aµdmu)s.ty10d5isoc,fethveenobifjeitctdsoweserneontohtavdeisatinngeuxicsehsasbilneWfro1m−Wth2e bbyythhoetstphoretseomrovsatrviaabrilaebelxetoinbcjteicotnsidnueTatbolea1ro–taitsinggendeisrca.llHyoctasupsoetds dard S
backgroundinW4,havingS/Nvaryingfrom4.7to0.Theremaining inyoungstarsandbrowndwarfsarethoughttobeadirectconse- pac
11weredetectedwithS/N>5.0andhavethebrightestsignalsin quenceofaccretionandsotheyareevidenceoftheexistenceofa e F
W4.These11aremarkedwithringsinFigs1,2,3and4.Ofthe11, disc.Likewise,variableextinctionisalsoevidenceoftheexistence ligh
7 are in the population of 22 with distinct W1−W2 (3.4–4.6µm) ofadisc.AllfourobjectsareinthepopulationwithW1−W2colour t C
colourexcess. excess. tr o
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5 DISCUSSION ril 3
, 2
Inall,22objectswereidentifiedasclassIIobjectsonthebasisof 01
3
theirW1−W2colouralone.OneobjectwithasmallW1−W2excess
wasalsoplacedinthepopulationofclassIIobjectsbecauseofits
bright W3 signal. A further four other objects with no W1−W2
excess were also categorized as class II because of their bright
signals in the 22µm W4 passband. All 27 objects are listed in
Table2.Theremaining89objects(listedinTable3)weredeemed
to be class III, i.e. they have no discs or discs with a large inner
opacityholeofatleast5–20au(seeScholzetal.2007).Weshow
thespectralenergydistributionsforsixcharacteristicexamplesof
theclassIIobjectsinAppendixB.
Figure4. (W1−W2,J−K)colour–colourdiagramwithbrowndwarfsand 5.1 Discfraction
isochronesasinFigs1and2.ThetwoobjectswhicharebrightinW4and
whichshowsignsofaccretionhaveanexcessinbothW1−W2andJ−K. The overall disc fraction is 27 out of 116 or 23 ± 5percent (the
Apartfromthosetwo,therestofthepopulationwithexcessinW1−W2 uncertainty corresponds to a 1σ confidence interval based on bi-
showsnoobviousexcessinJ−K. nomial statistics). As noted in Section 2 above, contamination in
NewbrowndwarfdiscsinUpperScorpius 907
Table2. Positions,UKIDSSZandJphotometry,WISEW1,W2,W3andW4photometryofthe27classIIobjects.Objectsarelistedin
orderofdecreasingmass,basedontheirZmagnitude.CoordinatesareJ2000.
Name RA Dec. ZMag. JMag. W1Mag. W2Mag. W3Mag. W4Mag.
2MASSJ16075049−2125200 16:07:50.49 −21:25:20.2 14.03 12.69 11.27 10.73 9.10 7.22
2MASSJ15465432−2556520 15:46:54.32 −25:56:52.1 14.16 12.75 11.40 10.81 9.10 6.23
2MASSJ16052875−2655496 16:05:28.75 −26:55:49.7 14.18 12.89 11.67 11.21 9.90 8.03
2MASSJ16095852−2345186 16:09:58.52 −23:45:18.7 14.20 12.57 11.34 10.97 9.96 8.73a
2MASSJ16030235−2626163 16:03:02.36 −26:26:16.4 14.46 13.12 11.44 10.92 9.59 8.04a
2MASSJ15470374−2601183 15:47:03.74 −26:01:18.4 15.02 13.32 12.03 11.74 10.42 7.39
2MASSJ16134880−2509006 16:13:48.81 −25:09:00.7 15.04 13.56 11.96 11.32 9.55 7.58
2MASSJ15514709−2113234 15:51:47.09 −21:13:23.5 15.12 13.54 10.56 9.88 8.85 7.41
2MASSJ16035573−2738248 16:03:55.73 −27:38:25.1 15.19 13.80 12.70 12.45 12.13a 7.89
2MASSJ15472572−2609185 15:47:25.73 −26:09:18.5 15.40 13.55 11.87 11.51 9.58 7.37
2MASSJ16145253−2718557 16:14:52.53 −27:18:55.7 15.65 14.06 12.34 11.79 10.63 8.70a
2MASSJ15412655−2613253 15:41:26.55 −26:13:25.4 15.65 14.00 12.59 12.10 10.75 8.24a
2MASSJ15521088−2125372 15:52:10.88 −21:25:37.4 15.72 13.86 11.01 10.15 8.90 6.92 D
2MASSJ16143287−2242133 16:14:32.87 −22:42:13.5 15.82 14.16 12.88 12.34 11.74a 8.38a ow
n
2MASSJ15501958−2805237 15:50:19.58 −28:05:23.9 16.04 14.56 13.28 12.72 12.03a 8.98a lo
2MASSJ16080745−2345055 16:08:07.45 −23:45:05.6 16.06 14.40 12.86 12.21 10.30 8.43a ade
22MMAASSSSJJ1155552741581830−−22770151556607 1155::5527::4158..1831 −−2277::0151::5566..18 1166..1369 1144..4728 1133..0462 1122..3856 1110..9704a 98..0656aa d from
2MASSJ16142144−2339146 16:14:21.44 −23:39:14.8 16.59 14.97 13.57 12.99 11.95a 8.25a h
22MMAASSSSJJ1166011020263088−−22710287149440 1166::0110::2026..3098 −−2271::0287::1494..51 1166..6882 1144..7802 1133..2249 1122..5655 1111..9101a 88..7423aa ttp://m
2MASSJ15541998−2135428 15:54:19.99 −21:35:43.0 16.85 14.98 13.26 12.57 11.22 8.39a nra
2MASSJ16083048−2335109 16:08:30.49 −23:35:11.0 16.95 14.88 13.37 12.86 11.69a 8.63a s.o
x
2MASSJ16082847−2315103 16:08:28.47 −23:15:10.4 17.64 15.45 13.77 13.22 12.21a 8.34a fo
2MASSJ15472282−2139141 15:47:22.82 −21:39:14.3 17.97 15.65 13.69 13.07 11.63a 8.67a rdjo
22MMAASSSSJJ1155545333691447−−22554365559419 1155::5453::3369..1457 −−2255::4365::5594..29 1188..2135 1155..8737 1133..6931 1133..1723 1110..1707a 77..9728 urnals
aS/N<5. .org
a/
Table3. Positions,UKIDSSZandJphotometry,WISEW1,W2,W3andW4photometryofthe89classIIIobjects.Objectsarelistedin t N
A
orderofdecreasingmass,basedontheirZmagnitude.CoordinatesareJ2000. S
A
G
Name RA Dec. ZMag. JMag. W1Mag. W2Mag. W3Mag. W4Mag. o
d
d
a
2MASSJ16175608−2856399 16:17:56.09 −28:56:40.0 14.01 12.76 11.76 11.53 10.54 8.17a rd
2MASSJ16034797−2801319 16:03:47.97 −28:01:31.9 14.03 12.81 11.83 11.62 11.17 9.02a Sp
a
2MASSJ16105728−2359540 16:10:57.28 −23:59:54.1 14.04 12.80 11.68 11.48 11.72a 8.72a ce
22MMAASSSSJJ1156505545282998−−22554566427278 1156::5055::4528..2999 −−2255::4566::4272..89 1144..0170 1122..6559 1111..5520 1111..2242 1100..9833a 89..1088aa Fligh
2MASSJ16105429−2309108 16:10:54.29 −23:09:11.1 14.13 12.97 11.88 11.68 11.60a 8.27a t C
2MASSJ15591513−2840411 15:59:15.12 −28:40:41.3 14.14 12.96 12.00 11.77 12.39a 8.75a tr o
n
2MASSJ16095217−2136277 16:09:52.17 −21:36:27.8 14.15 12.51 11.33 10.97 10.72 9.14a A
22MMAASSSSJJ1165046131659113−−22752309544487 1165::0461::3165..9114 −−2275::2309::5444..98 1144..1166 1122..8786 1111..8559 1111..6307 1111..9310a 88..7731aa pril 3
2MASSJ16033799−2611544 16:03:37.99 −26:11:54.4 14.17 12.98 11.96 11.70 11.22 8.63a , 20
2MASSJ16105499−2126139 16:10:54.99 −21:26:14.0 14.22 12.73 11.56 11.30 10.89 8.53a 13
2MASSJ16154869−2710546 16:15:48.69 −27:10:54.7 14.22 12.82 11.69 11.40 11.65a 8.86a
2MASSJ15450519−2559047 15:45:05.20 −25:59:04.7 14.23 12.90 11.76 11.54 12.00a 8.53a
2MASSJ16072196−2358452 16:07:21.96 −23:58:45.3 14.24 12.99 11.86 11.64 11.27 8.79a
2MASSJ16152819−2315439 16:15:28.19 −23:15:44.1 14.24 13.12 12.08 11.90 11.78a 8.18a
2MASSJ16370523−2625439 16:37:05.24 −26:25:44.0 14.27 12.96 11.96 11.69 11.40 8.91a
2MASSJ15492909−2815384 15:49:29.08 −28:15:38.6 14.29 12.96 11.85 11.63 12.05a 8.91a
2MASSJ15491602−2547146 15:49:16.02 −25:47:14.6 14.31 13.01 11.87 11.60 10.90 8.20a
2MASSJ16082229−2217029 16:08:22.29 −22:17:03.0 14.31 12.94 11.85 11.56 11.10 8.81a
2MASSJ16061595−2218279 16:06:15.95 −22:18:28.0 14.31 13.17 12.11 11.91 11.92a 9.02a
2MASSJ15544260−2626270 15:54:42.61 −26:26:27.0 14.32 13.05 11.91 11.72 11.61a 8.23a
2MASSJ16090168−2740521 16:09:01.68 −27:40:52.3 14.33 12.86 11.71 11.44 10.97 8.72a
2MASSJ15582376−2721435 15:58:23.76 −27:21:43.7 14.35 13.07 12.02 11.79 11.37a 8.78a
2MASSJ16132180−2731219 16:13:21.80 −27:31:22.0 14.36 13.25 11.93 11.85 11.60a 8.77a
2MASSJ15415562−2538465 15:41:55.63 −25:38:46.5 14.37 13.10 12.02 11.79 12.14a 8.93a
2MASSJ16002535−2644060 16:00:25.35 −26:44:06.1 14.38 13.02 11.90 11.66 11.67a 8.50a
908 P.Dawsonetal.
Table3 – continued
Name RA Dec. ZMag. JMag. W1Mag. W2Mag. W3Mag. W4Mag
2MASSJ15545410−2114526 15:54:54.11 −21:14:52.7 14.40 13.26 12.10 11.94 10.71 8.31a
2MASSJ16062637−2306113 16:06:26.37 −23:06:11.4 14.48 13.20 12.12 11.87 11.68a 8.90a
2MASSJ16121609−2344248 16:12:16.09 −23:44:25.0 14.50 13.19 11.96 11.78 10.99 8.21a
2MASSJ16090451−2224523 16:09:04.51 −22:24:52.5 14.57 12.92 11.66 11.40 10.59 8.23a
2MASSJ16113470−2219442 16:11:34.70 −22:19:44.3 14.61 13.24 12.11 11.87 12.25a 8.77a
2MASSJ15505993−2537116 15:50:59.94 −25:37:11.7 14.62 13.33 12.30 12.05 11.55a 8.90a
2MASSJ15524857−2621453 15:52:48.57 −26:21:45.4 14.62 13.30 12.27 12.00 12.51a 9.14a
2MASSJ16372782−2641406 16:37:27.83 −26:41:40.7 14.63 13.30 12.14 12.00 11.42 8.95a
2MASSJ15522943−2721003 15:52:29.44 −27:21:00.4 14.64 13.47 12.45 12.14 12.36a 9.06a
2MASSJ15530374−2600306 15:53:03.75 −26:00:30.7 14.66 13.43 12.36 12.14 12.03a 8.62a
2MASSJ15493660−2815141 15:49:36.59 −28:15:14.3 14.66 13.39 12.36 12.05 11.63a 8.79a
2MASSJ16133476−2328156 16:13:34.76 −23:28:15.7 14.74 13.48 12.39 12.12 11.77a 8.81a
2MASSJ15490803−2839550 15:49:08.02 −28:39:55.2 14.82 13.60 12.45 12.21 10.68 8.15a
2MASSJ16112630−2340059 16:11:26.30 −23:40:06.1 14.83 13.40 12.16 11.92 12.04a 8.55a D
2MASSJ15495733−2201256 15:49:57.33 −22:01:25.7 14.89 13.35 12.15 11.89 11.56a 8.64a ow
n
2MASSJ16062870−2856580 16:06:28.70 −28:56:58.2 14.90 13.52 12.39 12.18 11.41 9.06a lo
2MASSJ15572692−2715094 15:57:26.93 −27:15:09.5 14.93 13.66 12.59 12.39 12.00a 9.10a ade
22MMAASSSSJJ1166106045523695−−22383132401837 1166::1060::4552..3696 −−2238::3132::4019..60 1145..9094 1133..7537 1122..6428 1122..3237 1111..6719aa 89..4143aa d from
2MASSJ16132665−2230348 16:13:26.66 −22:30:35.0 15.05 13.52 12.33 11.99 11.00 8.82a h
22MMAASSSSJJ1166101654793170−−22221156036862 1166::1016::5479..3170 −−2222::1156::0368..84 1155..0079 1133..6773 1122..5613 1122..2347 1111..7960aa 88..8749aa ttp://m
2MASSJ15585793−2758083 15:58:57.93 −27:58:08.5 15.13 13.81 12.78 12.54 12.08a 9.06a nra
2MASSJ15420830−2621138 15:42:08.31 −26:21:13.8 15.15 13.74 12.59 12.32 12.10a 9.07a s.o
x
2MASSJ16090197−2151225 16:09:01.98 −21:51:22.7 15.16 13.59 12.32 12.08 10.87 8.45a fo
2MASSJ16124692−2338408 16:12:46.92 −23:38:40.9 15.18 13.60 12.42 12.19 12.20a 8.25a rdjo
22MMAASSSSJJ1166115334624684−−22331051127759 1166::1153::3462..4684 −−2233::1051::1278..60 1155..1199 1133..9732 1122..8457 1122..6215 1122..0230aa 88..2338aa urnals
2MASSJ16113837−2307072 16:11:38.37 −23:07:07.5 15.19 13.74 12.60 12.31 11.97a 8.59a .o
2MASSJ15583403−2803243 15:58:34.03 −28:03:24.5 15.21 13.72 12.53 12.30 11.45 9.03a arg/
2MASSJ16192399−2818374 16:19:23.99 −28:18:37.5 15.29 13.79 12.73 12.40 11.51a 8.57a t N
2MASSJ15490414−2120150 15:49:04.14 −21:20:15.2 15.31 13.77 12.64 12.37 11.50a 8.92a A
S
2MASSJ16051243−2624513 16:05:12.43 −26:24:51.4 15.40 14.06 12.93 12.76 12.29a 9.08a A
2MASSJ15533067−2617307 15:53:30.68 −26:17:30.7 15.49 13.99 12.83 12.60 12.06a 8.64a Go
2MASSJ15544486−2843078 15:54:44.85 −28:43:07.9 15.51 14.12 12.99 12.81 12.60a 8.90a dd
a
2MASSJ15531698−2756369 15:53:16.98 −27:56:37.2 15.53 13.96 12.84 12.55 12.50a 8.58a rd
2MASSJ15551960−2751207 15:55:19.59 −27:51:21.0 15.60 14.03 12.93 12.67 12.30a 9.10a Sp
2MASSJ15564227−2646467 15:56:42.28 −26:46:46.8 15.62 14.03 12.85 12.54 11.65a 8.51a ace
22MMAASSSSJJ1166110115341369−−22825366340981 1166::1101::1534..1359 −−2282::5366::3419..03 1155..6773 1144..0267 1123..8094 1122..5890 1121..1866aa 98..0392aa Fligh
2MASSJ16092938−2343121 16:09:29.39 −23:43:12.2 15.96 14.20 12.94 12.65 12.30a 8.98a t C
2MASSJ16103014−2315167 16:10:30.14 −23:15:16.8 16.06 14.37 13.05 12.75 11.97a 8.35a tr o
2MASSJ15561721−2638171 15:56:17.21 −26:38:17.2 16.10 14.52 13.26 13.00 10.38 8.23a n A
22MMAASSSSJJ1166017422604611−−22174445146997 1166::0174::2260..4611 −−2217::4445::1479..18 1166..1371 1144..6409 1133..4232 1132..1973 1122..2266aa 88..5659aa pril 3
2MASSJ15572820−2708430 15:57:28.21 −27:08:43.0 16.40 14.78 13.71 13.47 12.21a 8.77a , 20
2MASSJ16134079−2219459 16:13:40.79 −22:19:46.1 16.49 14.72 13.42 13.08 12.05a 8.99a 13
2MASSJ15442275−2136092 15:44:22.75 −21:36:09.3 16.55 15.01 13.69 13.48 11.68a 8.55a
2MASSJ15543065−2536054 15:54:30.65 −25:36:05.5 16.73 15.03 13.80 13.61 11.58a 8.17a
2MASSJ16064818−2230400 16:06:48.18 −22:30:40.1 16.82 14.93 13.63 13.37 12.04a 8.68a
2MASSJ15444172−2619052 15:44:41.72 −26:19:05.3 17.16 15.21 13.86 13.63 12.26a 8.86a
2MASSJ16072382−2211018 16:07:23.82 −22:11:02.0 17.24 15.20 13.70 13.41 12.20a 8.87a
2MASSJ16104714−2239492 16:10:47.13 −22:39:49.4 17.44 15.26 13.80 13.51 12.02a 8.57a
2MASSJ16084744−2235477 16:08:47.44 −22:35:47.9 17.74 15.69 14.30 14.11 12.28a 8.79a
2MASSJ15491331−2614075 15:49:13.32 −26:14:07.5 18.29 16.04 14.50 14.12 12.16a 8.88a
2MASSJ16081843−2232248 16:08:18.43 −22:32:25.0 18.51 16.10 14.28 14.05 11.56a 8.72a
2MASSJ16195827−2832276 16:19:58.26 −28:32:27.8 18.74 16.18 14.42 14.10 12.47a 8.77a
2MASSJ15451990−2616529 15:45:19.91 −26:16:53.0 18.77 16.27 14.41 14.06 11.85a 8.20a
2MASSJ16362646−2720024 16:36:26.47 −27:20:02.5 18.77 16.33 14.52 14.22 11.44a 8.79a
2MASSJ16360175−2703305 16:36:01.75 −27:03:30.5 19.12 16.64 14.95 14.91 12.07a 8.86a
2MASSJ16073799−2242468 16:07:37.99 −22:42:47.0 19.24 16.76 15.16 14.73 12.51a 8.25a
2MASSJ15504498−2554213 15:50:44.99 −25:54:21.4 19.90 16.93 14.86 14.70 11.84a 8.33a
aS/N<5.
NewbrowndwarfdiscsinUpperScorpius 909
oursampleappearstobenegligible.Conservativelyassumingthat
10percentoftheobjectsarecontaminantswhichdonotexhibitmid-
infraredexcesswouldonlyincreasethediscfractionto27/104,i.e.
26percent. This contrasts with the previous results for UpSco of
37±9percent(Scholzetal.2007)obtainedwithasmallersample
of35objects.Thesampleof35objectsinScholzetal.(2007)was
selectedfromthesurveysof(Ardila,Martin&Basri2000,12ob-
jects)and(Martinetal.2004,23objects).Thehigherdiscfraction
reportedinScholzetal.(2007)maybetheresultofusingasmaller
sampleofobjectsorofapossiblebias.
TheresultsofScholzetal.(2007)werealsoincontrasttothedisc
fractionof19percentforK0–M5starsinthesameregionobtained
byCarpenteretal.(2006)usingasampleof127K0–M5stars.Our
newresult,of23±5percent,fromasimilarlysizedsampleof116
objects,isstatisticallyindistinguishablefromtheresultofCarpenter
etal.(2006),suggestingthatdisclifetimesinUpScoforobjectslater Figure5. DiscfractionsforK/Mstarscomparedtodiscfractionsforbrown
D
thanK0shownodependenceonthemassofthecentralobject.We dwarfsinCha1,IC348,σOriandUpSco.Ineachcasethediscfractionfor ow
notethatfromoursampleof27discs,22(from72,31percent)are theK/Mstarsisstatisticallyindistinguishablefromthediscfractionforthe nlo
foundtobeinthemassrange0.01–0.05M(cid:2),whileonly5(from browndwarfs(seethetext;Section5.1). ad
e
d
4in4d,ic1a1tepearctreennt)datroewianrdtshehimghaesrsdraisncgefra0c.0ti5o–n0s.0fo9rMve(cid:2)ry. Tlohwismmaasys hasthesmallestdiscfraction,norobustcorrelationcanbesafely from
brown dwarfs, but it is not sufficiently robust to warrant further determined in respect of the disc fractions and ages of the four http
discussion. associations. ://m
n
ra
s
.o
5.1.1 Discfractionsinotherclusters x
5.2 Transitiondiscs fo
rd
ThisresultforUpScocanbecomparedwiththoseforChaI(Luhman jo
Objectswithverylittleornoexcessatnear-tomid-infraredwave- u
et al. 2005; Damjanov et al. 2007), IC 348 (Luhman et al. 2005; rn
Lada et al. 2006) and σ Ori (Hernandez et al. 2007), three other lengthsbutexhibitingexcessatlongerwavelengthsarebestunder- als
stoodbyassuminganopacityholeintheinnerdisc(seeSection5.3). .o
associationsforwhichsimilarinformationisavailable.Damjanov rg
etal.(2007)reportadiscfractionof52±6percentfromasample Theymaybeintheprocessofclearingdustfromtheirinnerdiscs a/
(Calvetetal.2002;Muzerolleetal.2006).Suchobjectsareoften t N
of 81 K3–M8 objects in Cha I, while Luhman et al. (2005) find A
a disc fraction of 50 ± 17percent from a much smaller sample termed ‘transition discs’, but the criteria used to define transition SA
of18objectslaterthanM6.Luhmanetal.(2005)alsofindadisc discsdifferintheliterature(seeMerinetal.2010;Luhman&Ma- G
fractionof42±13percentfor24objectslaterthanM6inIC348, majek2012foradiscussionofthevariouscriteria).Hereweuse odd
whereLadaetal.(2006)reportadiscfractionof47±12percent thetermtoidentifyobjectswithlittleornoexcessinW1−W2,i.e. ard
in the range of K6–M2 stars. In an analysis of discs in σ Ori, shortwardsof10µm,butbrightW3and/orW4signals(seeSections Sp
Hernandezetal.(2007)findadiscfractionof36±4percentfor 4.1.3and4.1.4).Thefiveobjectsthatsatisfythiscriterionarein- ace
sdtwarasrfisnt(hdeefimnaesdsraasnogbej0e.c1ts–1<.00M.1(cid:2)Ma(cid:2)nd).3T3h±e s1p0epcetrracletnytpfeosrborfowthne cfrlouWmdeedcdlaionssnthoIIetfitconlacdslsaasnIsIyIgoIrIbo.juepctatnhdatmmaiyghbtebiencthalelepdroac‘epsrseo-tfratrnasnitsiiotinoanl Flight C
mostmassivestarsinthisrangedefinedbyHernandezetal.(2007) disc’(Espaillatetal.2008,2012),showingevidenceforanopacity tr o
are a little earlier than K (up to G8). However, the vast bulk of gap (as opposed to an inner hole) in the disc, i.e. with excess at n A
theirsampleisinthemassrangeofKandMstars,sotheirresult p
is noted here as being valid for K and M stars in σ Ori. Fig. 5 <10µm,noexcessat12µmandexcessagainat22µm. ril 3
showsthatinthewakeofthisrevisionoftheresultsforUpSco,all Basedonouradopteddefinition,thefractionoftransitiondiscs , 20
aroundclassIIbrowndwarfsinoursampleis5/27or19percent. 1
fourassociationsnowshowsimilardiscfractionsforK/Mstarsand 3
Due to the small sample size, the uncertainty in this number is
brown dwarfs. Thus, average disc lifetime does not appear to be
in the range of ±10percent. Taking this into account, the value
dependentonthemassofthecentralobjectinanyoftheseregions.
is consistent with most previous estimates for the transition disc
fraction for low-mass stars which are, for criteria similar to the
oneadoptedhere,intherange0–20percent(e.g.Ercolano,Clarke
5.1.2 Theagesoftheassociations
& Robitaille 2009; Muzerolle et al. 2010). Thus, based on our
All the associations listed above are young, i.e. <10Myr old. estimateforthebrowndwarfregime,thereisnoevidenceformass
Preibischetal.(2002)determinedanageofabout5MyrforUp- dependenceinthetransitiondiscfrequency.
Sco, while a revised age of 10Myr has been proposed by Pecaut The small number of transition discs in our sample indicates
etal(2012).ChaI,IC348andσ Orihaveeachhadvariousages thatthetransitionphaselastsonlyashorttimecomparedwiththe
ofbetween2and5Myrreportedforeachofthem(Oliveiraetal. total lifetime of the discs. Assuming the upper limit for the age
2002; Zaptero Osorio et al. 2002; Luhman et al. 2003; Luhman spreadof2Myr(Preibisch&Zinnecker1999),weobtainanupper
2004,2007;Sherry,Walter&Wolk2004;Mayneetal.2007).So limitof0.4Myrforthetransitiontime-scale,i.e.aboutoneorder
whileUpScoappearstobetheoldestofthefourassociations,Cha ofmagnitudeshorterthanthedisclifetime.Thus,atwotime-scale
I, IC 348 and σ Ori cannot yet be readily distinguished in terms modelfortheevolutionofthediscs,asoftenadoptedforlow-mass
of their ages. Ergo, apart from stating that the oldest association stars,isrequiredforbrowndwarfsaswell.
910 P.Dawsonetal.
thelinesproposedbyDullemond&Dominik(2004).Ergo,inthis
5.3 Radiativetransfermodels
model,theprocessoftransitionfromclassIItoclassIIIthatmay
Scholzetal.(2007)producedmodelspectralenergydistributions beoccurringaroundthisobject’sdiscdoesnotrequirethepresence
based on Monte Carlo radiative transfer simulations for the 13 ofmechanisms(e.g.planetformation)thatwouldcompletelyclear
class II objects that they found in UpSco. Fig. 6 shows the spec- theinnerdisc.
tral energy distributions of the two of those objects recovered in
thiswork,whichhavebeenrecreatedusingtheoriginalmodelpa-
rameters.DatashownfortheJ,H,K,9,10,11and24µmwave-
5.4 ComparisonwithRiazetal.(2012)
lengthsaretakenfromthatofScholzetal.(2007).Thenewdata
fortheW1,W2andW3passbandsarealsoshownoverplottedon Inarecentpaper,Riazetal.(2012)analyseasampleof43spec-
thetwospectralenergydistributiondiagrams.ItisclearfromFig.6 troscopically confirmed very low mass members (spectral types
thatthedataforW1(3.4µm),W2(4.6µm)andW3(12µm)agree M4–M8.5)inUpScousingWISEdata.TheyfindsixnewclassII
verywellwithbothoriginalmodels,lyingonorveryclosetothe objectsandrecoverfourotherspreviouslyrecordedbyScholzetal.
modelledfluxforacombinedphotosphereanddisc(solidlinesin (2007)andafurthertwothatwerefoundbySlesnick,Hillenbrand
Fig.6). &Carpenter(2008).These12objectsarelistedintheirtable1.We
Models of the inner part of a disc rely on observational data havebeenkindlyprovidedwithatablewhichincludesthe31other
D
in the mid-infrared to refine their accuracy. Scholz et al. (2007) browndwarfsthattheyinvestigatedandcategorizedasclassIIIby ow
notedthatthegapintheirdatacoverageinthe3–8µmregionre- Riaz(privatecommunication).Fromthe12classIIand31classIII nlo
a
stricted their ability to constrain the size of any inner disc holes objectsthattheylist,thereare12incommontoboththatstudyand d
e
idnitisoonurocefsththeatWexh1ibainteddWe2xcdeastsaespaotin9tsµmforantdhebetwyoondo.bTjehcetsadin- othuerss.aBmoethsesvteundioebsjeccattsegaosrcizlaessthIeIIs.amefiveobjectsasclassIIand d from
FpriogTb.he6edn.doawtaaflolorwtshethoebajceccutriancythoefltehfet-mhaonddelpsainnetlhiwsarsegoiroingitnoalblye owfitAthhleSso/WNi3n<csl3iug.d0neaidnlaitnhnedthWree3qtaupbiarlseestsbhuaapntpdal.iRseodiuabzrcyeetRhaiala.vz(e2a0are1W2s)ix3reoSlty/hNoenrofot≥hbeje3uc.s0tes. http://mn
fitted with a model which included an excess in the mid-infrared Asaresulttheydonotcategorizethesesixbrowndwarfs.However, ras
whichnecessitatedthepresenceofanopticallythickinnerdisc.The using the W1−W2 colour as a primary diagnostic instead of W3 .ox
fo
newlyoverplottedW1(3.4µm)andW2(4.6µm)valuesobserved allows a larger range of objects to be successfully examined. All rd
byWISEconformwiththatpartofthemodel,furtherindicationthat 116 objects investigated in our work have an S/N > 8 in the W1 jou
asignificantW1-W2excessisevidenceforthepresenceofadisc. andW2passbands,whileonly64ofthemhaveanS/Nof≥3.0in rna
The W1−W2 excess for this object places it more than 4σ away theW3passband.Thesixobjectswhichcannotbecategorizedin ls.o
fromtheisochroneinthe(W1−W2,Z)colour–magnitudediagram Riazetal.(2012)becausetheyhaveaweakW3signalhavebeen arg/
inFig.1. determinedinthisworktobeclassIIIobjectsusingtheirW1and t N
A
The diagram in the right-hand panel of Fig. 6 is for the object W2signalsalone. S
notedinSections4.1.3and5.2abovethatmaybeintheprocessof RequiringthatasourcehaveaW3S/Nof≥3.0notonlyrestricts A G
transitionfromclassIItoclassIII.ItslesserexcessatW1andW2is thenumberofobjectsinanysamplefromUpSco,butalsoproduces od
d
clear,asisitsrelativelygreaterexcessatW3.Again,theaccuracyof asamplethatisbiasedwithrespecttothepresenceofdiscs.ClassIII ard
theoriginalmodelatthesewavelengthsisconfirmedbythenewly objectsinUpScoarelesslikelythanclassIIobjectstohaveastrong S
p
observedWISEvalues.Whilethemodelshowndoesprecludethe W3signal.Ofthe116objectsexaminedinthiswork,78percentof ac
e
existence of an optically thick inner disc, it does not require the theclassIIobjects,butonly48percentoftheclassIIIobjects,have F
presenceofanevacuatedholeintheinnerdisc.Instead,areduced aW3S/Nof≥3.0.Restrictingtheanalysistothose64objectsonly ligh
scaleheight,i.e.aflatterinnerdiscissufficient.Thisevolutiontoa wouldhaveyieldedanartificiallyhighdiscfractionof33percent, t C
flatterdisccouldbecausedbygraingrowthanddustsettlingalong ratherthanthe23percentfoundfromthelargerunbiasedsample tr o
n
A
p
ril 3
, 2
0
1
3
Figure6. SpectralenergydistributionforthetwoclassIIobjectsoriginallyidentifiedinScholzetal.(2007)andrecoveredinthiswork.Datashownare
takenfromthatofScholzetal.(2007)fortheJ,H,K,9,10,11and24µmwavelengths,alongwiththenewlyacquiredW1,W2andW3values.TheMonte
CarloradiativetransfersimulationsshownforcomparisonusethesameparametersasweregiveninScholzetal.(2007).Thedottedlinesdepictcalculated
photosphericfluxwhilethesolidlinesrepresentcombinedphotosphericanddiscflux.
NewbrowndwarfdiscsinUpperScorpius 911
of116objects,whilealsoincreasingthestatisticalerrors.Forthese Examining all the UKIDSS, 2MASS and WISE colour–
reasonsourdiscfractionisamorerepresentativevalueforthebrown magnitude and colour–colour combinations shows that the WISE
dwarfpopulationinUpSco. W1−W2colouristhebestprimarydiagnosticforthepresenceofa
discaroundtheobjects.
27classIIobjectsareidentifiedfromthesample.22wereclassi-
5.5 ComparisonwithLuhman&Mamajek2012 fiedviatheirW1−W2colourexcessalone.Fiveotherobjectswere
alsocategorizedasclassIIfromtheirW3and/orW4signals.These
AnotherrecentpaperfocusedonthediscsofUpScomembershas
fiveobjects(19percentofalldiscs)appeartobeinthetransition
been published by Luhman & Mamajek (2012). Similar to Riaz
phasebetweenclassIIandclassIII,leadingtotheconclusionthat
etal.(2012)theylookatasampleofspectroscopicallyconfirmed
thisphaseisshortlived,lastinglessthan0.4Myr,anestimatethat
members. Their list of targets includes 387 objects with spectral
isconsistentwithfindingsforlow-massstars.
typesM4–M8andanother23withM8–L2andisthussubstantially
Thediscfractionisfoundtobe23±5percent.Thisfractionis
largerthantheRiazetal.sample.TheyanalysetheavailableSpitzer
statisticallyindistinguishablefromresultsforK/MstarsinUpSco.
andWISEphotometryfortheseobjects.Toidentifytheobjectswith
ResultsfromtheliteratureforChaI,IC348andσ Orishowthat
discs,theyusethespectralregimefrom4.5to24µm,similartothis
theirbrowndwarfdiscfractionsarealsoindistinguishablefromtheir
paper.
K/Mstardiscfractions.Therefore,theaveragelifetimeofthediscs
48 of their targets also appear in our total sample of 119, D
ineachoftheseregionsshowsnoobviousdependenceonthemass ow
aomuroncglasthsemII/I1I3I cdliasstisnificteidonasacglraesessIIwiinththtihsepaopneer.iInnLmuohsmtcaanse&s, of the central object. Combined with the short transitional phase nloa
fromclassIItoclassIII,thissuggeststhattheevolutionofbrown d
Mamajek(2012).TheonlyexceptionistheM9–L1object2MASSJ ed
1b6as0e8d28o4n7i−tsW2311−51W023,cowlohuicrh,wchleearerlaysLfuulhfimlsanou&r MclaasmsaIjIekcr(i2t0er1i2o)n dstwarasr.fdiscsfollows‘atwotime-scalemodel’,similartolow-mass h from
concludethatitisdisklessbasedonitsK−W2colour.Attheselate ttp
spectraltypes,however,theintrinsiccoloursofyoungbrowndwarfs ACKNOWLEDGMENTS ://m
n
increasesignificantly withspectral typeand cover abroad range, TheauthorswouldliketothankIsabelleBaraffeofExeterUniver- ras
i.e.itischallengingtounambiguouslydistinguishbetweenclassII .o
sityandFranceAllardoftheCentredeRechercheAstrophysique x
and class III. Whether this source does or does not have infrared fo
deLyonforsupplyingmodeldata.ThisworkwassupportedbySci- rd
excessemissionremainstobedetermined,butthisdoesnotaffect enceFoundationIrelandwithintheResearchFrontiersProgramme jou
ourresultsinanyway. undergrantno.10/RFP/AST2780.Thispublicationmakesuseof rna
Theremainderofoursample(71intotal,amongthem14with ls
dataproductsfromtheWISE,whichisajointprojectoftheUni- .o
doiusrcws)oirsknienwcreaansdesnothtecsoavmerpeldeboyfbLruohwmnadnw&arfMsaanmaalyjesked(2w0i1th2)m,ii.de-. voerarstoitryy/oCfalCifaolrinfoiarnIinas,tiLtuotseAofnTgeeclehsn,oalongdy,thfeunJdeetdPbroyptuhlesiNonatiLoanba-l at Nrg/
infrareddatasignificantly. A
AeronauticsandSpaceAdministration.Thispublicationalsomakes S
ThediscfractionderivedbyLuhman&Mamajek(2012)forvery A
lowmassandsubstellarmembersofUpScois∼25percent,andthus useofdataproductsfromtheTwoMicronAllSkySurvey,whichis G
ajointprojectoftheUniversityofMassachusettsandtheInfrared od
agreesverywellwithourownresult.Theyalsofindthatdiscfrac- d
ProcessingandAnalysisCenter/CaliforniaInstituteofTechnology, a
tionsincreasefromverysmallvaluesforB–Gstars(≤10percent) rd
fundedbytheNationalAeronauticsandSpaceAdministrationand S
to25percentfor≥M5objects.Thisseemsatoddswithourown p
theNationalScienceFoundation.Wewouldalsoliketothankthe ac
statement of spectral type-independent disc fractions, but a more UKIDSSTeamfortheexcellentdatabasetheyhavemadeavailable e F
detailedexaminationshowsthatthetwostudiesactuallygivecon- tothecommunity. ligh
sistentresultsforKandMstars. t C
Luhman&Mamajek(2012)reportdiscfractionsof6/67forK0– tr o
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912 P.Dawsonetal.
EspaillatC.etal.,2012,ApJ,747,103 performs photometric and astrometric calibrations. The resulting
HaischK.E.,Jr,LadaE.A.,LadaC.J.,2001,ApJ,553,L153 reducedimageframesandcataloguesarethenplacedintheWF-
HernandezJ.etal.,2007,ApJ,662,1067 CAMScienceArchive(WSA).TheWSAcanbeinterrogatedusing
JayawardhanaR.,CoffeyJ.,ScholzA.,BrandekerA.,vanKerkwijkM.H., StructuredQueryLanguage(SQL).
2006,ApJ,648,1206
AsshowninFig.A1,thenewareainUpScoinvestigatedhere
LadaC.J.etal.,2006,AJ,131,1574
andsurveyedfortheNinthDataReleasecovers24deg2.Thedata
LawrenceA.etal.,2007,MNRAS,379,1599
LodieuN.,HamblyN.C.,JamesonR.F.,2006,MNRAS,373,95 forobjectsinthetargetareawereobtainedviaanSQLquerytothe
UKIDSSGCSdatabase.Allquerieswerestructuredtoincludeonly
LodieuN.,HamblyN.C.,JamesonR.F.,HodgkinS.T.,CarraroG.,Kendall
T.R.,2007,MNRAS,374,372 pointsourceobjectsinordertoavoidcontamination byextended
LodieuN.,HamblyN.C.,JamesonR.F.,HodgkinS.T.,2008,MNRAS, sources(e.g.relativelynearbygalaxies).Aseveryobjectwithpho-
383,1385 tometriccharacteristicsconsistentwithabrowndwarfhaditsproper
LodieuN.,DobbieP.D.,HamblyN.C.,2011,A&A,527A,24 motionassessed,inordertocheckwhetheritislikelyamemberof
LuhmanK.L.,2004,ApJ,602,816 UpSco, each query submitted also correlated all objects found in
LuhmanK.L.,2007,ApJS,173,104 theUKIRTGCSdatabaseswiththosefoundin2MASSdatabases.
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The2MASSdataareusedasafirstepochforthepurposesofproper
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motioncalculation.
BouvierJ.,LadaC.J.,2003,ApJ,593,1093 D
o
LuhmanK.L.etal.,2005,ApJ,631,L69 w
n
MartinE.L.,DelfosseX.,GuieuS.,2004,AJ,127,449 A1 Photometry loa
MayneN.J.,NaylorT.,LittlefairS.P.,SaundersE.S.,JeffriesR.D.,2007, de
d
MNRAS,375,1220 AquerysimilartothatshowninDawsonetal.(2011)wassubmitted fro
MerinB.etal.,2010,ApJ,718,1200 totheWSA.Thequeryreturned1438887objects. m
MMuuzzAeeprrooJll,ll7ee0JJ8..,,eA1t1lal0le.7n,2L0.,0M6,eAgpeaJ,th64S3.,T1.,0H0e3rnandezJ.,GutermuthR.A.,2010, Jse,aZTr)chhceo,olabojnueerc–wtmsqwaugeenrreiytuawdsseaesdsssiaeugdbrmoanmitttehadesbstohaostihwsenoWfintShFeAiigre.plAioms2ii.tniToaontinroegnfiaanle(lZothb−e- http://mn
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NattSa.,A2.0,T0e2s,tAiL&.,AC,o3m93e,r5n9F7.,D’AntonaF.,BaffaC.,ComorettoG.,Gennari from (Z − J, Z) = (1.0, 14.0) through (1.4, 16.6) to (3.0, 21.55) .oxfo
(dashedlineinFig.A2).Thisqueryleft4398objects.Reddening rd
OliveiraJ.M.,JeffriesR.D.,KenyonM.J.,ThompsonS.A.,NaylorT., jo
2002,A&A,382L,22 causedbyextinctionshiftsobjectstotherightanddownoncolour– urn
PecautM.J.,MamajekE.E.,BubarE.J.,2012,ApJ,746,154 magnitudediagrams.Toassessifreddeningwascontaminatingthe als
PreibischT.,ZinneckerH.,1999,AJ,117,2381 results,the4398objectshadtheirlocationplottedasshowninthe .org
PreibischT.,BrownA.G.A.,BridgesT.,GuentherE.,ZinneckerH.,2002, right-handpanelofFig.A1.Thereisanobviousclusteringofobjects a/
AJ,124,404 in a large area which coincides with the heavily extincted region t N
Riaz B., Lodieu N., Goodwin S., Stamatellos D., Thompson M., 2012, aroundρOph.Therefore,theanalysiswasconfinedto706638ob- AS
MNRAS,420,2497 jectsintheNinthDataReleasethatwereoutsidethatregion(dashed A G
ScholzA.,JayawardhanaR.,WoodK.,MeeusG.,StelzerB.,WalkerC., linesinFig.A1).Thisleftonly200ofthe4398objectsselectedin od
SchOol’zSAul.l,ivXaunXM.,.,J2ay0a0w7,aArdphJa,n6a6R0,.,1W51o7odK.,Eislo¨ffelJ.,QuinnC.,2009, theinitial(Z−J,Z)cut.These200objectswereexaminedagain dard
inthe(Z−J,Z)colour–magnitudediagram.86oftheobjectsto S
MNRAS,398,873 p
SherryW.H.,WalterF.M.,WolkS.J.,2004,AJ,128,2316 theleftoftheline(Z−J,Z)=(1.1,14.0)through(1.1,14.3),(1.2, ace
SkrutskieM.F.etal.,2006,AJ,131,1163 14.9),(1.3,15.2),(1.6,17.0)to(3.0,21.0)wererejectedforbeing Flig
SlesnickC.L.,CarpenterJ.M.,HillenbrandL.A.,2006,AJ,131,3016 toofarfromtheisochroneontheblueside,leaving114photometric h
SlesnickC.L.,HillenbrandL.A.,CarpenterJ.M.,2008,ApJ,688,377 candidates. t C
WrightE.L.etal.,2010,AJ,140,1868 tr o
n
ZapateroOsorioM.R.,BejarV.J.S.,PavlenkoYa.,ReboloR.,Allende A
PrietoC.,MartnE.L.,GarcaLpezR.J.,2002,A&A,384,937 A2 Propermotion pril 3
The114photometriccandidateswerethenexaminedtofindtheir , 2
0
proper motion. The resulting vector point diagram is shown in 1
3
Fig. A3. The known proper motions of UpSco in right ascension
APPENDIX A: NEW OBJECTS FROM UKIDSS
anddeclinationareabout−11masyr−1and−25masyr−1,respec-
NINTH DATA RELEASE
tively (de Bruijne et al. 1997; Preibisch et al. 2002). Of the 114
Thissectionoutlinesthemethodusedtoidentifynewbrowndwarfs candidates,4weretoofainttoberecordedin2MASSleaving110
in UpSco using the UKIDSS Ninth Data Release. It is the same candidateswithpropermotiondatacalculated.Theremaining110
methodasusedbyDawsonetal.(2011)toanalysetheEighthData candidatesincluded14withpropermotionsgreaterthantherange
Release.Forthesakeofbrevity,someofthedetailsdescribedby ofFig.A3.
Dawsonetal.(2011)arenotrepeatedhere. All96candidates showninFig.A3arepredominantlycentred
UKIDSSismadeupofseveralcomponentsincludingtheGalactic aroundthe(−11,−25)position.A2σ selectioncircleascalculated
ClusterSurvey(GCS).DescribedindetailinLawrenceetal.(2007), inDawsonetal.(2011)isshowncentredonthatposition.Thereis
theGCSisasurveyof10largeopenstarclustersandstar-forming nosignificantclusteringofobjectsaroundthe(0,0)positionindi-
regions,includingUpSco. catingthatthesampleisnotcontaminatedbymoredistantobjects,
TheinstrumentusedtotaketheGCSimagesistheWideField e.g.AGBstarswhichhavesimilarsurfacetemperaturesandcolours
Camera (WFCAM). Data collected by the WFCAM is subject to to brown dwarfs, but much greater intrinsic luminosities. The 76
an automated process that detects and parameterizes objects and candidates within the 2σ selection circle were then classified as