The embedded clusters DBS 77, 78, 102, and 160-161 and their link with the interstellar medium

2.3 MB·

by  M. A. Corti

Astronomy&Astrophysicsmanuscriptno.IRpaper160111 (cid:13)cESO2016
January13,2016
The embedded clusters DBS77, 78, 102, and 160−161 and their link
with the interstellar medium(cid:63)
M.A.Corti1,2,G.L.Baume1,3,J.A.Panei1,3,L.A.Suad2,J.C.Testori2,J.Borissova4,5,R.Kurtev4,5,A.N.Chené6 &S.
RamirezAlegría4,5
1 FacultaddeCienciasAstronómicasyGeofísicas,UniversidadNacionaldeLaPlata,PaseodelBosques/n,B1900FWALaPlata,
Argentina
2 InstitutoArgentinodeRadioastronomía(CCT-LaPlata,CONICET),C.C.No.5,1894VillaElisa,Argentina
3 InstitutodeAstrofísicadeLaPlata(CCT-LaPlata,CONICET-UNLP),PaseodelBosques/n,B1900FWALaPlata,Argentina
4 InstitutodeFísicayAstronomía,UniversidaddeValparaíso,Av.GranBretaña1111,PlayaAncha,Casilla5030,Chile
6 5 MillenniumInstituteofAstrophysics(MAS),Av.GranBretaña1111,PlayaAncha,Casilla5030,Chile
1 6 GeminiObservatory,NorthernOperationsCentre,670NorthA’ohokuPlace,Hilo,HI96720,USA
0
2 Received***;accepted****

n
a ABSTRACT
J
2 Aims.WereportastudyoftheglobalpropertiesofsomeembeddedclustersplacedinthefourthquadrantoftheMilkyWaytoclarify
1 someissuesrelatedwiththeirlocationintodeGalaxyandtheirstellarformationprocesses.
Methods.Weperformed BVI photometricobservationsintheregionofDBS77,78,102,160,and161clustersandinfraredspec-
] troscopyinDBS77region.TheywerecomplementedwithJHKdatafromVVVsurveycombinedwith2MASScatalogue,andused
R mid-infraredinformationfromGLIMPSEcatalogue.WealsosearchedforHIdatafromSGPSandPMNradiosurveys,andprevious
S spectroscopicstellarclassification.Thespectroscopicandphotometricinformationallowedustoestimatethespectralclassificationof
thebrighteststarsofeachstudiedregion.Ontheotherhand,weusedtheradiodatatoinvestigatetheinterstellarmaterialparameters
.
h andthecontinuumsourcesprobablyassociatedwiththerespectivestellarcomponents.
p Results.Weestimatedthebasicphysicalparametersoftheclusters(reddening,distance,age,andinitialmassfunction).Wesearched
- for HII regions located near to the studied clusters and we analyzed the possible link between them. In the particular case of
o
DBS160−161clusters,weidentifiedtheHIbubbleB332.5-0.1-42locatedaroundthem.Wefoundthatthemechanicalenergyinjected
r
t totheinterstellarmediumbythemoremassivestarsofthiscoupleofclusterswasenoughtogeneratethebubble.
s
a Keywords. Stars:early-type–Stars:pre-mainsequence–Stars:formation–ISM:structure–radiolines:ISM
[

1
v1. Introduction ofthecorrespondingcolorexcess,absorptionsandreddeningbe-
8 havior.
1Embeddedclustersprovideanimportanttooltoinvestigatestel-
Duringthelastyears,severalsystematicsearchesofembed-
7larproperties,theinterstellarmedium(ISM),andthestructureof
dedclustershavebeendevelopedbasedonnewinfraredskysur-
2theGalaxy(Pinheiroetal.2012).Inparticular,severalembedded
veys.Inparticular,thoseworksusingVistaVariablesintheVía
0clustersincludemassivestarsandpresentimportantpremainse-
.quence(PMS)populations(Chenéetal.2013).Theyallowusto Láctea (VVV)1 survey (e.g. Borissova et al. 2011, 2014; Barba
1
et al. 2015). Our goal is to obtain the characteristic parameters
0studyearly−typestars,theirimpactonthesurroundingenviron-
ofalargesampleofembeddedclustersusinghomogeneousdata
6mentandhelptooutlinethepathofthespiralarms.TheOandB
andanalysismethods.Resultsforfourknownclusterswerepre-
1typestarsoftheseclustersemitlargeamountsofenergywhich
sentedbyChenéetal.(2012)andforsixofthenewVVVcluster
:modify the properties of the surrounding ISM. These interac-
v candidateswithWolf-Rayet(WR)starsinChenéetal.(2013).In
tionscausephotodissociationregionslikeHIIregions(Lequeux
Xi2005). The winds of the early stars can also originate bubbles, thispaperwefollowsimilaranalysismethodsasinthosepapers,
butweappliedthemtoasampleofclustersoftheDBScatalogue
ridentified as a minimum in the HI emission distribution sur-
aroundedbyregionsofhigheremissivity.TheseHIstructuresand (Dutraetal.2003)andwecomplementedthemwithopticaland
radiodata.
HIIregionsaresignaturesofstarformation.
Since embedded clusters are immersed in a large amount Inthepresentworkweinvestigatedtheregionsoftheembed-
of gas and dust, they are affected by high visual extinction. ded clusters DBS77, DBS78, DBS102, and DBS160-161. In
This makes necessary to employ infrared (IR) observations for ordertoestimatethefundamentalparametersoftheclustersand
a proper study. However, optical data, at least for the brightest their interaction with the ISM, we performed a multifrequency
clustermembers,areanimportanttooltoobtainreliablevalues study using optical, infrared, and radio data. All the selected
regions are located in the galactic plane in the fourth quadrant
(cid:63) Based on observations gathered as part of observing programs: of the Galaxy (see Table 1). They are probably associated with
179.B-2002,VIRCAM, VISTA at ESO, Paranal Observatory; 087.D-
0490A,NTTatESO,LaSillaObservatoryandCN2012A-045,SOAR
telescopeatNOAO,CTIO. 1 http://www.vista.ac.uk
Articlenumber,page1of15
A&Aproofs:manuscriptno.IRpaper160111
identifiedHIIregionsandsomeparticularobjects.Inthefollow- – BVI imagesobtainedbyuswiththeSouthernAstrophysical
C
ingwepresentabriefdescriptionofthem: Research(SOAR)4telescope.
– Data from the following surveys/catalogues: a) The VVV
– Embedded cluster DBS77 is placed near the recently iden- survey (Minniti et al. 2010; Saito et al. 2012), b) The
tified clusters VVV15 and VVV16 (Borissova et al. 2012) APASS5catalogue(Hendenetal.2010)oftheAmericanAs-
usingVVVsurvey.Thesethreeclustersarelocatedcloseto sociation of Variable Star Observers (AAVSO) c) The Two
the dark nebula Dobashi 5898 (Dobashi 2011) that was re- Micron All-Sky Survey (2MASS)6, (Skrutskie et al. 2006),
vealed from near infrared observations from 2MASS data. d) The GLIMPSE catalogue from Spitzer Space Telescope
They seem to be associated with the IRAS source 12320- (SST) data. e) Infrared spectroscopy gathered from New
6122 and placed inside the HII region RCW65 = Gum43. TechnologyTelescope(NTT)7attheEuropeanSouthernOb-
All the complex is inside the molecular cloud G301.0+1.2. servatory (ESO), La Silla Observatory and f) The South-
Theyarealmostinthesamelineofsightthattheforeground ernGalacticPlaneSurvey(SGPS)8 (McClure-Griffithsetal.
open cluster Ruprecht105 placed at 950 pc (Kharchenko 2005)andtheParkes-MIT-NRAO(PMN).9
etal.2005).
– Embedded cluster DBS78 is associated with the IRAS
source12331-6134andplacedinsidetheultracompactHII 2.1. Images
region GRSG301.11+00.97 (Bronfman et al. 1996). They
2.1.1. Opticaldata
are located in the molecular cloud G301.1+1.0 (Russeil &
Castets2004)andclosetothedarknebulaDobashi5905. We used BVI images that we acquired using the SOAR Opti-
C
– Embedded clusterDBS102is inthe coreof theHII region calImager(SOI)mountedattheSOAR4.1mtelescopeatCerro
G333.0+0.8(Kuchar&Clark1997)whichissurroundedby TololoInter−AmericanObservatory(CTIO,Chile).Thiscamera
several (∼ 20) dark and molecular clouds identified by the hasamini-mosaicoftwothinnedandbackilluminatedE2V2k×
analysis of mid infrared images produced by Spitzer, avail- 4kCCDs.Wesetabinningfactorof2×2andthenweobtaineda
ableviaGalacticLegacyInfraredMidplaneSurveyExtraor- scalevalueof0(cid:48).(cid:48)153/pix,andthemosaiccovers,approximately,
dinaire(GLIMPSE)2.TheanalysisoftheMultibandInfrared afieldofview(FOV)of5.(cid:48)2×5.(cid:48)2.Weobtainedthreeshiftedim-
Photometer for Spitzer Galactic survey (MIPSGAL)3 data agesoneachfieldforeachfilter(seealsoTable2).Imageswere
(Peretto&Fuller2009)isanotherinformationsource.These acquired in 2012 during thenight of May 15th. The typical full
molecular clouds were also identified by the CO observa- width at half maximum (FWHM) was ∼ 2(cid:48)(cid:48) and airmass values
tions(Russeil&Castets2004).Closetotheclusterislocated wereabout1.3-1.5.
thedarknebulaDobashi6419.Inallthesecloudsyoungstel- All frames were pre−processed in the standard way using
larobjects(YSOs)havebeenidentifiedfromGLIMPSEdata theIRAF10taskESOWFI/MSCRED.Thatis,instrumentaleffects
(Robitailleetal.2008). werecorrectedwithcalibrationimages(biasandsky−flatstaken
– EmbeddedclustersDBS160andDBS161formacouplelo- duringthesameobservingnight).Theexposuresforeachband
catedatthecenteroftheHIIregionG332.5−00.1(Kuchar& were combined using IRAF MSCIMAGE task. This procedure
Clark1997;Bronfmanetal.1996)andareidentifiedwiththe allowedustofilltheinter-chipgapsoftheindividualimages.It
IRASsource16132-5039whichisalsosurroundedbyabout alsowasusefultoremovecosmicraysandtoimprovethesignal
20-30darkandmolecularcloudsidentifiedbyCOobserva- tonoise(S/N)forthefinalimages.
tions(Russeil&Castets2004).Theanalysisofmidinfrared
images produced by Spitzer and MIPSGAL data is another
informationsource.TherearealsothreesourceswithIRex- 2.1.2. Infrareddata
cess according to the Midcourse Space Experiment (MSX)
Inordertostudythephotometricbehavioroftheselectedclus-
data(Eganetal.2003).Allthisregionispartoftheextended
ters(seeTable1),weusedthestackedimagesoftheindividual
starformationcomplexRCW106(Bainsetal.2006).These
10.(cid:48)0×10.(cid:48)0exposurescontainingtheselectedclustersfromthe
twoclustershavebeenstudiedbyRoman-Lopes&Abraham
VISTA Science Archive (VSA website11; see Saito et al. 2012
(2004) using near infrared (NIR) photometric observations
formoredetailsaboutVVVdata).
andbyRoman-Lopesetal.(2009)throughthespectralclas-
sificationofthreestarsintheregion.Twoofthemidentified
asearlymainsequence(MS)starsandthethirdoneclassified 2.1.3. Astrometry
asaYSO.
WorldCoordinateSystem(WCS)headerinformationwasavail-
Thispaperisorganizedasfollows:Section2reportsthedif- ableonlyforVVVimages,thereforeweusedALADINtooland
ferent sources of the analyzed data and the way they were pro- 2MASS data to obtain this information for our optical images.
cessed.Section3describesthemultifrequencystudycarriedout Ouradoptedproceduretoperformtheastrometriccalibrationof
over the described data. Section 4 presents a description of the ourdatawasexplainedinBaumeetal.(2009).Thisallowedus
characteristics found on each cluster region. In Section 5.1 we toobtainareliableastrometriccalibration.Thermsoftheresid-
discuss the interpretation of some particular results and in Sec-
4 http://ast.noao.edu/facilities/soar
tion6wepresentourfirstconclusions.
5 http://www.aavso.org/apass
6 http://www.ipac.caltech.edu/2mass/
2. Data 7 https://www.eso.org/sci/facilities/lasilla/telescopes/ntt.html
8 http://www.atnf.csiro.au/research/HI/SGPS/queryForm.html
Thisstudymakesuseofthefollowingmaterial: 9 http://www.parkes.atnf.csiro.au/observing/databases/PMN/PMN.html
10 IRAF is distributed by NOAO, which is operated by AURA under
2 http://www.astro.wisc.edu/glimpse/ cooperativeagreementwiththeNSF.
3 http://irsa.ipac.caltech.edu/data/SPITZER/MIPSGAL 11 http://horus.roe.ac.uk/vsa/
Articlenumber,page2of15
Cortietal.:EmbeddedclustersandtheISM

N NN
3
N
DBS 77 DBS 78
8
103 27
17 5 78 100
62
E vvv 15 EE 113
21
E
39
87
b) 1’
a) vvv 16
1’

N 1’ N
DBS 102b DBS 161 77 DBS 160
183 126
662 382
92 122
93
175
DBS 102a
E E
20 Comp.
Field
Comp.
Field 1’
c) d)

Fig.1. JHK false-colorVVVimagesofthefourstudiedregions.Selectedclustersareasareindicatedbybigyellowsolidcircles.Comparison
fieldsarealsoindicatedwithdottedcirclesinpanelsc)andd).IdentifiedstarsarethoseoneswithNIRspectroscopydataoradoptedbrightest
clustersmembers.Starsinsidecirclesareadoptedclustersmembers.(seetextandTable6).
Table1.Mainparametersofthestudiedembeddedclusters
Cluster α δ R V −M E SpT∗ U(cid:5) Age◦ Γ•
J2000 J2000 0 V B−V
ID [h:m: s] [◦:(cid:48):(cid:48)(cid:48)] [(cid:48)] [mag] [mag] [pccm−2] [Myr]
DBS077 12:34:52.0 -61:39:00.0 1.75 13.2 1.70 O7V(cid:52) 240(cid:52) ∼6.4(cid:52) −1.44±0.14(cid:52)
VVV016 12:35:00.0 -61:41:40.0 1.00 13.2 1.70
DBS078 12:36:03.0 -61:51:00.0 1.30 13.2 3.00 B1.4V 7 <20 −1.19±0.22
DBS102a 16:15:01.0 -49:50:41.0 1.00 12.6 2.50 O5(cid:52) 78(cid:52) ∼4(cid:52) −0.75±0.27(cid:52)
DBS102b 16:15:13.6 -49:49:07.0 1.00 12.6 2.50
DBS160 16:16:55.5 -50:47:26.0 0.75 12.3 2.50 B0V(cid:52) 49(cid:52) <10(cid:52) −0.71±0.61(cid:52)
DBS161 16:17:05.5 -50:47:29.0 1.00 12.3 2.50
Notes.(∗) FromtheearliestMSstaroneachclusterregion.((cid:52)) Parameterobtainedconsideringbothclustersasone.((cid:5)) Ionizationparameter(see
Eq.10,sec.3.7)(◦)Upperagelimit(Ekströmetal.2012)(•)IMFslopeobtainedwiththeMSandPMSstars.
ualsinthepositionswere∼0(cid:48).(cid:48)16,whichisabouttheastrometric (PSF)method(Stetson1987)ontheBVI and JHK images.The
precisionofthe2MASScatalogue(∼0(cid:48).(cid:48)12). PSF for each image was obtained from several isolated, spa-
tially well distributed, bright stars (∼ 10). The PSF photome-
try was aperture-corrected for each filter. Aperture corrections
2.1.4. Photometry were computed performing aperture photometry of the same
stars used as PSF models. All resulting tables were combined
InstrumentalmagnitudeswereobtainedusingIRAFDAOPHOT using DAOMASTER code (Stetson 1992) obtaining one set for
package. We search for stars on the optical and infrared im- BVIbandsandotherforJHK ones.
ages using DAOFIND task. In the optical case, this task was Unfortunately,thenightoftheopticalimageswasnotphoto-
performed over a white image obtained adding all the images metric.Thereforeour BVI datawerecalibratedusingthepho-
C
for individual filters. We employed the point spread function tometric values provided by APASS catalogue, that is B band
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Table2.DetailofopticalandIRscientificframes 2.1.5. Midinfrareddata
Band exptime[sec]×N• Wecross−correlatedourphotometricdatawithmidIRdata(on
the regions where these data are available) with the purpose of
B 20×3
detectingPMSstars(seealsoSect3.4).
V 20×3 We used then, the MSX data (Egan et al. 2003) and SST
I 100×3 data.MSXmappedthegalacticplaneandotherregionsmissed
C
or identified as particularly interest by the Infrared Astronom-
J 10
ical Satellite (IRAS) at wavelengths of 4.29, 4.35, 8.28, 12.13,
H 10 14.65and21.3µm.Ontheotherhand,theInfraredArrayCam-
K 10 era(IRAC)on-boardtheSSTwasusedtoobtainimagesinfour
channels(3.6,4.5,5,8and8.0µm)andtheGLIMPSEcatalogue
Notes.(•)N =amountofobservedframes wasproducedusingseveralofthesephotometricdatapoints.
We used then the all matches option in ALADIN since this
option gave us all the counterparts within the searching radius.
andSloangribandsfor∼10−20starsoneachclusterregion.We
Followingthesecriteria,wefoundabout10counterpartsinMSX
transformed the gri data to the VI system using the equations
C andGLIMPSEdataoneachclusterregion(seeSect.4formore
provided by Jester et al. (2005). To tie our observations to the
details).
standardsystem,weusedtransformationequationsoftheform:
b= B+b1+b2(B−V) (1) 2.1.6. Finalcatalogues
We used the STILTS12 tool to manipulate tables and to cross-
correlate the optical and IR data. We obtained then four cata-
v=V+v +v (B−V) (2) logueswithastrometric/photometricinformationofabout76000
1 2
objects covering approximately a FOV of 10.(cid:48)0 × 10.(cid:48)0 around
eachstudiedcluster(seeFig.1).Thecorrespondingphotometric
errors (BVIJHK bands) in these catalogues are those provided
i= I+i +i (V−I) (3) by DAOPHOT and DAOMASTER codes. The full catalogues
1 2
areavailableinelectronicformattheCDSwebsite.
whereBVIandbviarethetransformedAPASSandinstrumental
magnitudes,respectively.
2.2. Spectroscopicdata
The calibration of infrared JHK data was done using the
information of common stars with 2MASS catalogue on each Weperformedspectroscopicobservationsovereightstarsinthe
cluster region. To join the obtained magnitudes from the VVV region of DBS77 embedded cluster distributed in three slit po-
images,wetried tousetransformationswiththeformgiven by sitions.WeusedtheinfraredspectrographSofI13 ontheNTTat
Sotoetal.(2013).Howeverwenoticedinsomecases,adepen- LaSillaObservatoryESO,Chileinlong-slitmode,in2011dur-
denceoftheresidualswiththestellarmagnitude.Thereforewe ing the night of April 17th. Using the medium resolution grism
adoptedthefollowingdependences: inthe3rd order,wecoveredthewholeK band,2.00-2.30µm,
S
witharesolutionof∆λ4.66Å· pix−1.Weuseda1arcminslit,
j= j1+ j2J+ j3(J−H) (4) in order to match the seeing, which gives a resolving power of
R(cid:39)1320.ForoptimalsubtractionoftheatmosphericOHemis-
sionlines,weused15sec(IDstars:5;8and3;slit1);100sec
(IDstars:17and27;slit2)and150sec(IDstars:103;21;and
h=h1+h2H+h3(J−H) (5) 39;slit3)whilenoddingalongtheslitinanABBApattern:the
starwasobservedbefore(A)andafter(B)afirstnodalongthe
slit,thenatpositionBasecondtimebeforereturningtoposition
Aforalastexposure.TheS/NforeachspectrumisgiveninTa-
k=k1+k2K+k3(J−K) (6) ble6.Asameasureoftheatmosphericabsorption,weobserved
brightstarsofspectraltypeG.Weusedthestandardprocedures
where JHK and jhkare,respectively,2MASSandinstrumental toreducethedata.Formoredetailsofourreductionprocedures
VVVmagnitudes. seeMoorwoodetal.(1998)andChenéetal.(2012,2013).
The calibration coefficients of optical an infrared calibra-
tionequationswerecomputedusingFITPARAMS taskofIRAF
PHOTCALpackage.TheobtainedvaluesareshownatTable3. 2.3. Radiodata
InordertocompleteourdataforsaturatedstarsinVVVim- Withtheaimtoinvestigatetheinterstellarmediuminwhichthe
ages,wesimplyadoptedthe2MASSmagnitudesforthebright- star clusters are forming, we consulted the HI SGPS data from
estobjects(K <11). the Australia Telescope Compact Array (ATCA) and the PMN
Regarding the errors of our photometry, for BV and JHK surveycarriedoutwiththeParkes64mradiotelescopeandthe
bandstheycanbeestimatedfromtheircorrespondingrmsvalues NRAOseven-beamreceiver.
obtainedinthefittings(seeTable3)andcomplementedwiththe The SGPS is a survey of 21−cm HI spectral line emission
errorvaluesprovidedbyDAOPHOT andDAOMASTERcodes andcontinuum.TheHIdatawereobtainedusingachannelsep-
foreachparticularobject(seeSect.2.1.6).Forthespecialcaseof
Iband,theseerrorsmustbealsocomplementedwiththesystem 12 http://www.star.bris.ac.uk/mbt/stilts/
transformationerror(∼0.03;Jesteretal.2005). 13 http://www.eso.org/sci/facilities/lasilla/instruments/sofi.html
Articlenumber,page4of15
Cortietal.:EmbeddedclustersandtheISM
Table3.Calibrationcoefficientsusedforopticalandinfraredobservations
Coef. DBS DBS DBS DBS
077 078 102 160-161
b 0.48±0.02 0.94±0.01 -0.23±0.02 –
1
b -0.13±0.02 0.10±0.02 -0.13±0.02 –
2
rms 0.03 0.03 0.02 –
v 0.01±0.02 1.52±0.02 -0.25±0.02 –
1
v 0.09±0.02 0.29±0.02 0.07±0.02 –
2
rms 0.04 0.04 0.02 –
i 0.80±0.05 1.10±0.03 – –
1
i 0.01±0.04 0.17±0.02 – –
2
rms 0.07 0.06 – –
j 1.37±0.03 2.18±0.03 1.91±0.04 1.39±0.04
1
j 0.99±0.01 0.93±0.01 0.94±0.01 0.99±0.01
2
j -0.06±0.01 -0.02±0.01 -0.03±0.01 -0.06±0.01
3
rms 0.03 0.04 0.04 0.04
h 1.11±0.03 2.71±0.04 2.74±0.04 1.76±0.04
1
h 1.01±0.01 0.87±0.01 0.88±0.01 0.95±0.01
2
h -0.01±0.01 0.02±0.01 0.02±0.01 0.01±0.01
3
rms 0.03 0.04 0.04 0.05
k 2.27±0.04 4.25±0.04 4.64±0.03 2.60±0.03
1
k 0.98±0.01 0.82±0.01 0.78±0.01 0.94±0.01
2
k 0.01±0.01 0.01±0.01 0.00±0.01 0.01±0.01
3
rms 0.04 0.04 0.04 0.05
The 21−cm HI spectral line survey provides data covering
334912 253◦ ≤l≤358◦ and−1◦.5≤b≤+1◦.5,andasmallregioninthe
2.0 firstGalacticquadrantbetween5◦≤l≤20◦and−1◦.5≤b≤+1◦.5
212121 (SGPSI and SGPSII, respectively, see McClure-Griffiths et al.
10513033 (2005)fordetails).Thecontinuumsurveyonlyprovidesdataof
the253◦≤l≤358◦and−1◦.0<b<+1◦.0region(seeHaverkorn
C 1.5 232781 etal.(2006)fordetails).WeprocessedtheSGPScontinuumdata
+
ux 15178 usingtheNOD2package(Haslam1974).
d fl ThePMNisasouthernskysurveyatafrequencyofν=4.8
malize 1.0 134301 G∼H8zm. JTyhbeeaanmgu−l1a.rTrheesosluurtvioeynpirsov5i(cid:48)daensdsetvheerarlmpasrasmenestietirvsit(yfluixs
Nor 188 density,coordinates,angularsize,orientation,etc.)oftheHIdis-
1545 tributionfor−87◦≤δ≤10◦.
0.5
NIII
HeI HeII NaI FeI CaI MgI 3. Analysis
BrG
CO(2,0)
0.0 Employedmethodsfordeterminingthefundamentalparameters
2.10 2.15 2.20 2.25 2.30
oftheyoungstellarclusters,(sizes,extinctions,distances,ages,
Wavelength
members and masses) have already been described in several
Fig.2.StellarspectraintheDBS77region.Severalchemicalcompo- previouspapers(seee.g.Chenéetal.2012,2013;Baumeetal.
nentsofeachstararemarkedwithverticallines.Thespectraltypeof 2014).Here,weprovideabriefsummaryandhighlightwhatwe
eachstarisindicatedinTable6 havedonedifferentlyinthisstudy.
3.1. Centersandsizes
arationof ∆v = 0.82km s−1 andthe finalrms noiseof asingle The selected clusters are very faint and apparently have few
profileis∼1.6Konthebrightnesstemperature(T )scale.The members that makes difficult to apply the radial density pro-
b
sensitivity of the radio continuum data is below 1 mJy beam−1 filemethod.Wethenconsideredasthecentercoordinates,those
andtheangularresolutionoftheSGPSis1.(cid:48)6. given in the DBS catalog as an initial point and the visual in-
Articlenumber,page5of15
A&Aproofs:manuscriptno.IRpaper160111
spectionoftheinfraredimagestogetherwiththeresultingpho-
tometric diagrams using different centers and radii. We finally DBS 77
adoptedthosevaluesthatcontainthebrighteststarsandrevealed
01 16
thepresenceoftheprobablePMSpopulationinthesediagrams
(seeTable1).
DE 12
U
T
TI
A
3.2. Kinematicstudy C L
TI 08
C
Propermotionsandradialvelocitiesareveryusefultoolstoas- ALA
G
signclustermemberships.Unfortunately,theVVVdatabasecur-
04
rently contains observations covering four years and thus it is
possible to determine the proper motions only for nearby Sun
objects. On the other hand, the low resolution of the spectra, 00
-45 -35 -25 -15 -5
combined with the small wavelength coverage, does not allow
RADIAL VELOCITY (km/s)
a very accurate measurement of the radial velocities. Our data
were then not reliable to provide membership probability from
thekinematicbehavioroftheobjects.
Fig.3.T HIdistributionatDBS77region(l ∼ 301◦).Blackcurved
Underthissituation,wemadeuseofkinematicinformation linesindibcatetheplaceoftheHIIregion(RV= −46kms−1)andthe
ofHIIregions,molecularanddarkcloudsplacedprojectednear HIabsorptioninthelineofsight.Lowestandhighestcontoursare12.4
(∼10(cid:48))eachcluster.Wetransformedtheirradialvelocities(RV), Kand124K,respectively.Contourspacingis6Kuntil50Kand12
referred to the Local Standard of Rest (LSR) to kinematic dis- K from there onwards. Lighter gray color corresponds to the lowest
tances. In this procedure we used the Adjusted Linear Model temperaturevalue.
(AL) and the Law Potential Model (LP) given by Fich et al.
(1989) or the Galactic rotation model of Brand & Blitz (1993)
(see Sect. 4). The error in the determination of these kinematic
distances arises due to an uncertainty of 10 km s−1 due to non
01 06 (a)
circular motion (Burton 1988). The HI maps, RV vs b (Figs. 3 DBSD7B8S 78
to6),forallthestudiedregionsallowedustoresolvethedistance
aoamnbatbalyiignzeueditoykuirpnrpeohmbolatetomimcdepitrsreitscaendnciteasignryatihmeledsf(uossueretothSheGacvat.ela3ac.n4ti)cs.taqrutaindgrapnot.inTthtoe GALACTIC LATITUDE00 0528 (b)
54
3.3. Spectrophotometricanalysis
50
-45 -35 -25 -15 -5
Spectrophotometric color excesses and distances were calcu- RADIAL VELOCITY (km/s)
latedforthestarsforwhichweknowtheirspectralclassification
from our spectra or from the bibliography. Our spectroscopic
data involve some of the brightest stars of DBS 77 region and Fig.4.(a)SameasFig.3butatDBS78region(l ∼ 301◦).Lowestand
weusedthemtodeterminetheirspectralclassification,verifying highestcontoursare15Kand152K,respectively.Contourspacingis
15K.(b)Radiocontinuumemissionat1.42GHz.Lowestandhighest
their cluster membership situation. Spectral classification was
contoursare0.018and2.6Jybeam−1,respectively,withoutaconstant
performedusingatlasesof K−bandspectrathatfeaturespectral
step. Lighter gray color corresponds to the lowest flux value. Dashed
types stemming from optical studies (Rayner et al. 2009; Lier-
patterncircledrawnintheupperleft-handcornerindicatestheangular
mann et al. 2009; Meyer et al. 1998; Wallace & Hinkle 1997)
resolutionoftheHIdata.
(seeFig.2).
We used the optical (BVI) and infrared (JHK) data and
thecalibrationsgivenbySchmidt-Kaler(Th.1982)andKoorn-
data were used to check a consistent fit of the MS over all the
neef(1983),respectively.Weadditionallyevaluatedtheabsorp-
diagrams. To save space, we only present the optical diagrams
tions values on V and K bands as: AV = 3.1EB−V and AK = for the case of DBS 77 + VVV 16 region. In general, the pho-
0.674E ,validforanormalreddeninglaw(seeSect.3.4).For
J−K tometric diagrams revealed the presence of two stellar popula-
each cluster, we selected the stellar members for which we are
tions: a) the field population, usually late type MS stars, repre-
confidentoftheirspectraltypes.Weestimatedindividualstellar
sentedbythegroupplacedatleftinalldeCMDs(greysymbols
distancesthroughthemeanvalueofthecomputedV0−MV and along the diagrams), and b) the clusters populations suffering
K0−MK values. high and differential reddening and mixed with possible field
red giants. To separate both populations, we used (when avail-
able) the spectrophotometric analysis previously described, ob-
3.4. Photometricdiagrams
tainingthecorrespondingcolorexcessesandspectrophotometric
We checked the loci of the stars over all the possible distances. For stars without spectral classification, we used all
color−magnitud diagrams and two color diagrams (CMDs and the photometric diagrams and the reddening−free photometric
TCDs,respectively)obtainedfromourcatalogueandlocatedin- parameterQ =(J−H)−1.7(H−K)(Negueruelaetal.2007)
NIR
side the adopted clusters regions (see adopted centers and radii inordertoavoidtheintrinsicdegeneracybetweenreddeningand
for each cluster in Table 1). We present the corresponding dia- spectraltype.Inparticular,the(J−H)vs.(H−K)and/ortheK
gramsalongFigs.7to10.Inparticular,opticaldataareavailable vs. Q diagrams could be used to distinguish different stellar
NIR
foralltheselectedregions(exceptDBS160−161region).These populations.
Articlenumber,page6of15
Cortietal.:EmbeddedclustersandtheISM
wedonotprovideanunambiguousmembershipdiagnostic,but
DBSD1B0S21a0−2DaB−S110022bb
wedefinedauniformapproachtoselectthelikelymemberstars
00 54 (a) 00 54 (b) usedtocalculatetheclustersparameters.
52 To estimate the absolute magnitudes and spectral types for
GALACTIC LATITUDE 544086 GALACTIC LATITUDE 5406 twpothrauoeetrshdacadeoduroponepiptdcittldeeddetdhanMetveaiadrSlautinchnedletsueiastrrhtsnleeoodrcsccsteaitootaoimnronsnpewwusoitivtmathhetoirotorhutnehetsersMfepColeSerMcv.staDrtWunosdtsecif(eopoKdlrpleios<sctwea1onri3bnstsgwioenarrivtTnha1aots4birpolmdeenecas6--l,
44
42 pendingonthecluster).
42
40 38 3.5. IndividualstellarmassesandIMFcomputation
-120 -100 -80 -60 -40 -20 0 20
RADIAL VELOCITY (km/s) 04 333 00 56 332 52
GALACTIC LONGITUDE We obtained the stellar mass for the adopted cluster members
using the computed absolute magnitude values (see Sec. 3.4).
Fig.5.(a)SameasFig.4butatDBS102region(l ∼ 333◦).Herethe We employed the ZAMS obtained from Bressan et al. (2012);
HII region has RV = −52 km s−1. Lowest and highest contours are Chen et al. (2014); Tang et al. (2014); Chen et al. (2015) and
30Kand114K,respectively.Contourspacingis12K.(b)Lowestand we interpolated the stellar mass using the algorithm given by
highestcontoursinradiocontinuumemissionare0.1and2.7Jybeam−1, Steffen (1990). This procedure is valid only for MS stars, and
respectively,withoutaconstantstep. for adopted PMS stars is only provided an approximate upper
estimationoftherealmassvalues.
The initial mass function (IMF) for massive stars can be
DBSD1B60S−1D60B−S116611
modeledasapowerlaw.Thisis:
00 05
00 (a) -00 02 (b) log(N/∆(logm))=Γlogm (7)
00
GALACTIC LATITUDEGALACTIC LATITUDE--0000 1101005505 GALACTIC LATITUDE 0160 uu∆wse(hesleodrgfepomhrNo).etoaSimcsihnectthsreitecatrhb.neauTnmchdobesm,ererwpfuoeotrefoed,bststtaaopirnesebcdtupriaselldervtyetlhorpaegelaprIdiMoethpsFsme,inbidcwlesemmuapaadsossosnpvbttaheildne-
15
20 the mean mass value obtained from Martins et al. (2005) for
2250 O−spectraltypesandfromPecaut&Mamajek(2013)forBand
14 laterspectraltypes.
-120 -6-0100 -50-80 -40-60 -30-40 -20-20 -10 0 332 36 32 28
RRAADDIIAALL VVEELLOOCCIITTYY ((kkmm//ss)) GALACTIC LONGITUDE WebuilttwoIMFsforeachstudiedstellargrouptakinginto
accountonlytheadoptedMSstarsandaddingtheadoptedPMS
stars.Itmustbenoticedthattheuncertainlyintheirmassvalues
Fig.6.(a)MeanT HIdistributionatDBS160/161regionbetweenthe wasminimizedbytheusedwidthofthebinsintheIMFestima-
b
longituderangefrom332◦.52to332◦.55.Contourlevelsarefrom65K tion.OurresultsarepresentedinFig.11,togetherwiththeleast
to105Kinstepsof10K.Theellipseindicatestheinterstellarbubble squares fit for most massive stars (> 3 M ), avoiding the very
(cid:12)
(Fig.14).HIIregion(RV(cid:39)−47kms−1)isnotvisible(Bronfmanetal. probable incomplete less massive bins. We noticed that, except
1996).(b)SameasFig.5withthelowestandhighestcontoursindicated in the case of DBS77 region, the presence of PMS has an im-
0.04and1Jybeam−1,respectively,withoutaconstantestep. portanteffectontheobtainedslopevalues(seeTable1andFig.
11)
Inourprocedure,weadoptedasclustermembersthosestars
placedapproximatelyredderthananadoptedconsistentMS(red 3.6. Estimatingclusterages
curve) along all the photometric diagrams. We adopted the MS
calibrationsgivenbySchmidt-Kaler(Th.1982),Cousins(1978) Since all the clusters presented strong differential reddening
andKoornneef(1983).Theirlocationswerecomputedusingthe it was very difficult to estimate their ages using the classical
adopted distances and color excesses presented in Table 1 and method of fitting the observed CMD with isochrone sets. We
a normal reddening behavior (see Sect. 3.3) as was suggested therefore took into account the early spectral type of the stars
by TCDs diagrams. This fact allowed us to use the absorption adopted as cluster members and the Ekström et al. (2012) evo-
ratios (r = A /A ) given by Johnson (1968) van der Hulst lutionarymodelstocalculatetheMSdurationfromthemassof
X X V
curve15andCambrésyetal.(2002).Then,followingBorissova thestar.Incasewherespectroscopicdatawerenotavailable,we
etal.(2012)andMessineoetal.(2012)weseparatedtheselected used the estimated spectral classification from the photometric
stars among early normal MS stars (−0.1 < Q < 0.15; blue data(seeSect.3.4andTable6).Itmustbenoticedthattheesti-
NIR
symbols) and, stars with emission features or revealing IR ex- matedagevaluesareupperlimitssincethereveledhighamount
cess (Q < −0.1; red symbols), including for example PMS of PMS candidates suggest an active star formation process in
NIR
stars and YSOs. We noticed that some spectroscopically con- allthestudiedclusters.
firmedOBstarsinDBS77andDBS160regions(seeFigs.7and
10) have high Q values, but it could be a binarity effect. To
NIR 3.7. Studyingtheradiomaps
confirmthereliabilityofourprocedure,weconductedasimilar
analysisoveracomparisonfieldregionforeachcluster.Inthese The selected radio data (see Sect. 2.3) provide HI spectral line
cases, as was expected, we found almost no objects that could information over all the selected regions, but unfortunately, the
beconsideredclustermembers.Itmustbenoticed,however,that continuumsurveyonlyprovidesdatauntilb=1◦,forthisreason
Articlenumber,page7of15
A&Aproofs:manuscriptno.IRpaper160111
Fig.7.PhotometricdiagramsforthestarsinDBS77+VVV16regionandtheircorrespondingcomparisonfield(panelf).Squaresandcircles
representstarswithandwithoutknownspectralclassification,respectively.Lightgreysymbolsindicatefieldpopulationwhereasblueandred
representdifferentclusterpopulationsselectedbyourphotometricmethod(seetextinSect.3.4).Thesolid(red)anddotted(green)curvesarethe
ZAMSorMS(seetext)shiftedtheadopteddistancemoduliwithandwithoutabsorption/reddening,respectively.Dashed(red)linesindicatethe
normalreddeningpath(R =3.1).DashedcurvesareSiessetal.(2000)isochronesforz=0.02.
V
Fig.8.PhotometricdiagramsforthestarsinDBS78region.SymbolsasinFig7.
wecouldnotanalyzetheHIdistributionat1.4GHzforDBS77 a source free region located in the neighborhood. The obtained
region.Wederivedtheangulardiametersandfluxdensities(S ) fittedparametersarepresentedinTable4.
ν
of the radio continuum point sources found in the direction of In the direction of DBS 102 we found an extended source
DBS160−161andDBS78usingabidimenssionalgaussianfitto (for the angular resolution of the SGPS survey), with an angu-
theSGPScontinuumdata.Theerrorinthefitwasabout2%and lar size of 7.(cid:48)3 × 6.(cid:48)9. We calculated the integrated flux density
we determined a rms flux noise level of 0.013 Jy beam−1 from of the source using the method of polygon integrations and we
subtractedthebackgroundwithalinealbaselinefit.Thequoted
Articlenumber,page8of15
Cortietal.:EmbeddedclustersandtheISM
Fig.9.PhotometricdiagramsforthestarsinDBS102region.SymbolsasinFig7.
Fig.10.PhotometricdiagramsforthestarsinDBS160−161region.SymbolsasinFig7.
error reflected the uncertainties in determining the background the electronic density. This latter value was computed for each
levels,whichaddedupatotalofabout5%. region using a geometric model and employing the expression
Theemissionmechanismofthedetectedradiosourcescould givenbyMezger&Henderson(1967):
be identified using the spectral index α (S ∼ ν−α). This index
N [cm−3]=c a1/2635.1(T [104k])0.175(ν[GHz])0.05(S [Jy])1/2
wasobtainedfromthemeasuredfluxdensityattwodifferentfre- e 1 e ν
quencies,ν1 andν2 (α = log(S1/S2)/log(ν2/ν1)).Wecomputed (1/d[kpc])1/2(θG[arcmin])−1.5 (8)
thecorrespondingspectralindicesfortheradiosourcesfoundat where c = 0.775 is the conversion factor employed for the
1
thedirectionoftheclustersDBS78,DBS102,andDBS160-161 spheric geometric model adopted for the nebula, a = 1 is the
usingtheSGPSdata(1.4GHz)andthePMNdata(4.85GHz). recombination coefficient at all levels, T is the electronic tem-
e
Theα(cid:39)0.1valuesfoundwithbothfrequenciesrevealedaspec-
peratureobtainedfromthemodelofQuirezaetal.(2006),S is
ν
tra whose behavior was expected for an optically thin plasma. thefluxdensitymeasuredintheHIIregionatν=1.42GHzand
TheobtainedvaluesarepresentedinTable4.
θ is the observed apparent half-power beam width (HPBW),
G
The bidimensional gaussian fit and the method of polygon obtainedas:
integration(forpointorextendedsources,respectively)alsopro-
videdthepeakbrightnesstemperature(TC)foreachsourceat1.4 θG =(θsph1θsph2)1/2/1.471 (9)
GbyHBz.roTwhniseptaaral.m(2et0e1r4()ToCb),tafionrinthgedseiffreergeinotnsv,awluaess,ahlsoowceovmerputhteedy btheeinsgouθrscphe1inantdwθospphe2rptheendgiecoumlaertcriocomrdeiannatoesf.theobservedsizeof
employedthe"on-offmethod"(seeKolpaketal.2003).TheTC Moreover,usingmodelsofstellaratmospheresitispossible
values obtained by us and by Brown et al. (2014) are shown in to determine the total number (N ) of ionizing photons in the
Ly
Table4. Lymancontinuumofthehydrogenemittedbytheexcitingstar.
Theanalysisoftheobservationsintheradiocontinuumspec- We adopted the N values given by Smith et al. (2002). They
Ly
trumoftheopticallythinnebulaallowedustoestimatetheexci- calculatednon-LTE,line-blanketedmodelatmospheresforsev-
tationparameteru[pccm−2]=R N2/3.Thisvaluerepresentsthe eralmetallicitiesthatcovertheentireupperHertzprung−Russell
s e
LymanphotonnumberthatmightbeabsorbedbytheHIIregion diagramformassivestarswithstellarwinds.Wecomputedthen
to be ionized. The linear Strömgren radio, R , was obtained as N for adopted cluster members stars earlier than B2.0, since
s Ly
the geometric mean of the angular size of the source and N is theyprovidealmostallthesephotons.
e
Articlenumber,page9of15
A&Aproofs:manuscriptno.IRpaper160111
compared the excitation parameter u with the parameter U cal-
Γ=-1.44
3 Γ=-1.41 culatedwithEq.10foralltheexcitingstars.Thus,wecompared
DBS077 theobservationalresultsofdensityandradiusofthenebulawith
2.5 the flow of ionizing photons emitted by the exciting stars. The
M)) 2 comparisonallowedustodeterminewhethertheHIIregionde-
∆N/(log 1.5 vTihaeteosbftraoimnedthreesiudletaslocfotnhdeisteiocnosmapnadriwsohnastamreigdhitscbuestsheedcinauSseecs..
Log ( 5.2andarepresentedinTable4.
1 AnopticallythinHIIregionalsoallowedustoestimatethe
massofionizedhydrogenintheregionfollowingtheexpression
0.5
givenbyMezger&Henderson(1967).
0
0 0.5 1 1.5 2
Log (M/Mo) M [M ]=c a1/20.3864(T [104k])0.175(ν[GHz])0.05(S [Jy])1/2
HII (cid:12) 2 e ν
Γ=-1.19
3 Γ=-1.71 (d[kpc])2.5(θG[arcmin])1.5 (11)
DBS78
2.5
where c = 1.291 is the conversion factor employed for the
2
M)) 2 spheric geometric model adopted for the nebula and the other
∆log observablequantitiesarethesameasthoseusedinEq.8.
Log (N/( 1.5 FigsT.h3et2o16−)csmholwinezoenmeissswioitnhmloawpsvoaflutehseosftuTdi.edInrethgeiocnasse(seoef
1 b
DBS77,DBS78,andDBS102regions,theseminimacouldbe
0.5 interpretedastheresultoftheabsorptionoftheHIdistribution
indicating that T > T . On the other hand, the DBS160−161
c b
0 0 0.5 1 1.5 2 region,presentsaminimumintheHIemissiondistributionsur-
Log (M/Mo) rounded by enhanced HI emission, revealing the presence of a
3 ΓΓ==--01..7052 bubble. Interstellar bubbles are cavities with a minimum in the
center of its HI distribution expanding at relatively low veloci-
DBS102ab
2.5 ties(≤10kms−1)(Cappaetal.2003).
M)) 2
∆log
Log (N/( 1.5 4. Describingclustersregions
1
4.1. DBS77,VVV15,andVVV16
0.5
Since these threeclusters are placed atthe same studied region
andtheirphotometricdiagramsrevealedsimilarproperties,they
0
0 0.5 1 1.5 2 were studied as only one stellar group. We performed spectral
Log (M/Mo)
Γ=-0.71 classificationofeightstarsinthisregion(seeSect.2.2),obtain-
3 Γ=-1.38 ingthatthreeofthemcouldbeconsideredclustermembersand
DBS160−161 gaveusanspectrophotometricdistanceof4.6kpc(seeTable1).
2.5
The21−cmlineemissionmapinthisregion(seeFig.3)shows
M)) 2 that the largest HI absorption signature corresponds with a ve-
∆log locity value of − 46 km s−1. This value in this Galactic region,
N/( 1.5 has no distance associated from the kinematic rotation models
Log ( of the Galaxy (see Fig. 11), that means that this velocity is a
1 "forbidden value" for this models and the perturbations of the
rotationoftheGalaxycouldbecausingit.Theradialvelocityof
0.5
theregion,accordingtotheBrand&Blitz(1993)modelwould
0 beapproximately−33kms−1whichcorrespondstothetangen-
0 0.5 1 1.5 2
tial point linked to a distance of (cid:39) 4.6 ± 0.5 kpc. This value is
Log (M/Mo)
similartothespectrophotometriconepreviouslyindicatedandis
Fig.11.Distributionofstellarmassesforthestudiedembeddedclus-
consistentwithotherkinematicdeterminations(Fichetal.1989;
ters. Grey bars (light and dark) indicate more massive bins employed
for compute the IMF slopes (Γ). Light grey bars and blue solid lines Bronfman et al. 1996). Therefore, we adopted 4.6 kpc as the
mostreliabledistanceforthestudiedstellargroupinthisregion.
correspondtoonlyMSstars,whereasdarkgreybarsandblackdashed
linescorrespondtoMS+PMSstars. Our photometric analysis indicated the presence of an im-
portantamountofearlyMSstars(4Otypestarsand40Btype
stars) and, 13 probable PMS stars. In this region we found 6
Thus,theionizationparametercouldbecalculatedas:
MSXsourcescandidatestoYSOs,(Mottrametal.2007)with8
U[pccm−2]=[3N /4πa(2)]1/3 (10) possibleIRcounterparts.
Ly
Wecouldnotcalculatetheexcitationparameteruofthisre-
where a(2) = 2.76×10−13[cm3s−1] represents the probability gion because there are no map with HI emission distribution
of recombination at all levels except the ground level. We then datainthecontinuumat1.4GHz,forthisregion.
Articlenumber,page10of15