J/ApJ/945/108ivo://CDS.VizieR/J/ApJ/945/108doi:10.26093/cds/vizier/ba-xh-3cCDSJohnson J.R.Koplitz B.Williams B.F.Dalcanton J.J.Dolphin A.,Girardi L.2026-07-02T11:58:51Z2025-03-21T14:36:49ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgiant-starshst-photometryvisible-astronomyinfrared-photometrystellar-agesextinctionWe have combined resolved stellar photometry from Hubble Space Telescope (HST), Spitzer, and Gaia to identify red supergiant (RSG) candidates in NGC 6946, based on their colors, proper motions, visual morphologies, and spectral energy distributions. We start with a large sample of 17865 RSG candidates based solely on HST near-infrared photometry. We then chose a small sample of 385 of these candidates with Spitzer matches for a more detailed study. Using evolutionary models and isochrones, we isolate a space where RSGs would be found in our photometry catalogs. We then visually inspect each candidate and compare them to Gaia catalogs to identify and remove foreground stars. As a result, we classify 95 potential RSGs, with 40 of these being in our highest- quality sample. We fit the photometry of the populations of stars in the regions surrounding the RSGs to infer their ages. Placing our best candidate RSG stars into three age bins between 1 and 30Myr, we find 27.5% of the candidates falling between 1-10Myr, 37.5% between 10-20 Myr, and 35% between 20-30Myr. A comparison of our results to the models of massive star evolution shows some agreement between model luminosities and the luminosities of our candidates for each age. Three of our candidates appear significantly more consistent with binary models than single-star evolution models.2023ApJ...945..108Jhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/945/108CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toB/hst : HST Archived Exposures Catalog (STScI, 2007)I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)J/AJ/138/1003 : IR photometry of massive LMC stars (Bonanos+, 2009)J/ApJ/715/1094 : Census of self-obscured massive stars (Khan+, 2010)J/A+A/545/A43 : HII regions in NGC 628 and NGC 6946 (Cedres+, 2012)J/A+A/537/A146 : Stellar models with rot. 0.8<M<120, Z=0.014 (Ekstrom+, 2012)J/A+A/562/A75 : Spectra of 8 supergiants in nearby gal. (Britavskiy+, 2014)J/ApJ/791/105 : SNe progenitor masses prob. distribution (Williams+, 2014)J/ApJS/215/9 : PHAT X. UV-IR photometry of M31 stars (Williams+, 2014)J/ApJS/228/5 : Spitzer phot. of ~1million stars in M31 & 15 gal. (Khan, 2017)J/ApJ/846/145 : PHAT. XIX. Formation history of M31 disk (Williams+, 2017)J/ApJ/860/39 : HST observations of nearby core-collapse SNe (Williams+, 2018)J/A+A/622/A50 : Calibrated grid of rot. single star models (Higgins+, 2019)J/ApJ/881/54 : Masses of SNR progenitors in M83 (Williams+, 2019)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/945/108https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/945/108http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/945/108https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/945/108https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/945/108http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/945/108GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/945/108/candidates (Photometry for each candidate (Table 3) and full list of results from MATCH (Table 4))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/945/108/candidates?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/945/108/candidates?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/945/108/candidates?GETtext/xml+votable180.050000true308.603882160.15204610.005555555555555556Cone search capability for table J/ApJ/945/108/table1 (NGC 6946 HST observations)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/945/108/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/945/108/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/945/108/table1?GETtext/xml+votable180.050000true308.7449860.108880.005555555555555556Cone search capability for table J/ApJ/945/108/table2 (The position and photometry of our "HST Only" 17865 stars)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/945/108/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/945/108/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/945/108/table2?GETtext/xml+votable180.050000true308.589446360.14027410.0055555555555555566/15592-155933.036429446233786e-20 5.011627719502464e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/945/108?format=asciiOpticalInfrareddefaultJ/ApJ/945/108/candidatesPhotometry for each candidate (Table 3) and full list of results from MATCH (Table 4)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintID[51/6822] RSG candidate identifier (G1)meta.id;meta.mainintRAJ2000[308.6/308.85] HST Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000[60/60.2] HST Declination (J2000)degpos.eq.dec;meta.mainRASdeg[308.6/308.85] Spitzer Right Ascension (J2000)degpos.eq.raDESdeg[60/60.2] Spitzer Declination (J2000)degpos.eq.decF435Wmag[23.1/32]? HST ACS/WFC F435W band magnitude (1)magphot.mag;em.opt.BfloatnullableF606Wmag[21.1/29.8]? HST ACS/WFC F606W band magnitude (1)magphot.mag;em.opt.RfloatnullableF814Wmag[19.99/26]? HST ACS/WFC F814W band magnitude (1)magphot.mag;em.opt.IfloatnullableF110Wmag[18.93/22.37] HST WFC3 F110W band magnitudemagphot.mag;em.IR.JfloatF160Wmag[17.87/21.3] HST WFC3 F160W band magnitudemagphot.mag;em.IR.Hfloat3.6mmag[12.66/18.7] Spitzer/IRAC 3.6um band magnitudemagphot.mag;em.IR.3-4umfloat4.5mmag[12.89/19] Spitzer/IRAC 4.5um band magnitudemagphot.mag;em.IR.4-8umfloat5.8mmag[10.2/16.83] Spitzer/IRAC 5.8um band magnitudemagphot.flux.density;em.IR.4-8umfloatdAv[0/2.6]? Differential extinction within the region being measuredmagphys.absorption;arith.difffloatnullableAv[0.8/2.6]? Foreground extinction in the regionmagphys.absorptionfloatnullableAge[0/29]? Age resultMyrtime.ageintnullableFlagsCandidate status flag(s) (1)meta.code.errorcharK17Display data from Khan+ 2017, J/ApJS/228/5 within 1"meta.ref.urlcharJ/ApJ/945/108/table1NGC 6946 HST observationsIDImage identifiermeta.id;meta.maincharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintPID[12331/15216] Proposal identifiermeta.id;obs.proposalintObs[2010/2019] Year of the observationtime.epochRAJ2000[308.5/308.9] Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000[60/60.21] Declination (J2000)degpos.eq.dec;meta.mainV3-Axis[166.5/347] The V3 axisdegphys.angSizedoubleExp[99/987] Exposure timestime.duration;obs.exposureintFilterFilter namemeta.id;instr.filtercharJ/ApJ/945/108/table2The position and photometry of our "HST Only" 17865 starsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000[308.58/308.9] Right Ascension (J2000) (1)degpos.eq.ra;meta.mainindexedDEJ2000[60/60.23] Declination (J2000) (1)degpos.eq.dec;meta.mainindexedF435Wmag[21.66/39.2]? HST ACS/WFC F435W band magnitude (2)magphot.mag;em.opt.BfloatnullableF606Wmag[19.98/38.01]? HST ACS/WFC F606W band magnitude (2)magphot.mag;em.opt.RfloatnullableF814Wmag[19.46/31.7]? HST ACS/WFC F814W band magnitude (2)magphot.mag;em.opt.IfloatnullableF110Wmag[18.48/22.43] HST WFC3 F110W band magnitudemagphot.mag;em.IR.JfloatF160Wmag[17.4/21.3] HST WFC3 F160W band magnitudemagphot.mag;em.IR.Hfloat