J/AJ/143/74ivo://CDS.VizieR/J/AJ/143/74doi:10.26093/cds/vizier.51430074CDSBianchi L.Efremova B.Hodge P.Massey P.Olsen K.A.G.2017-10-09T13:34:49Z2013-05-21T08:00:11ZCDS support team

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

cds-question@unistra.frgalaxieshst-photometryultraviolet-astronomyearly-type-starsWe present a comprehensive study of young stellar populations in six dwarf galaxies in or near the Local Group: Phoenix, Pegasus, Sextans A, Sextans B, WLM, and NGC 6822. Their star-forming regions, selected from GALEX wide-field far-UV imaging, were imaged (at sub-pc resolution) with the WFPC2 camera on board the Hubble Space Telescope (HST) in six bandpasses from far-UV to IR to detect and characterize their hot massive star content. This study is part of HST treasury survey program HST-GO-11079; the general data characteristics and reduction procedures are detailed in this paper and results are presented for the first six galaxies. From a total of 180 HST images, we provide catalogs of the multi-band stellar photometry and derive the physical parameters of massive stars by analyzing it with model-atmosphere colors. We use the results to infer ages, number of massive stars, extinction, and spatial characteristics of the young stellar populations. The hot massive star content varies largely across our galaxy sample, from an inconspicuous presence in Phoenix and Pegasus to the highest relative abundance of young massive stars in Sextans A and WLM. Albeit to a largely varying extent, most galaxies show a very young population (a few Myrs, except for Phoenix), and older ones (a few 10^7^ years in Sextans A, Sextans B, NGC 6822, and WLM, ~10^8^yr in Phoenix and Pegasus), suggesting discrete bursts of recent star formation in the mapped regions. The hot massive star content (indicative of the young populations) broadly correlates with the total galaxy stellar mass represented by the integrated optical magnitude, although it varies by a factor of ~3 between Sextans A, WLM, and Sextans B, which have similar M_V_. Extinction properties are also derived.2012AJ....143...74Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/143/74CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toB/hst : HST Archived Exposures Catalog (STScI, 2007)II/312 : GALEX-DR5 (GR5) sources from AIS and MIS (Bianchi+ 2011)J/A+A/548/A129 : HST photometry in NGC 6822 (Fusco+, 2012)J/ApJ/706/599 : H{alpha} and UV SFR in the local volume (Lee+, 2009)J/ApJS/173/538 : XUV-Disk galaxies in the Local Universe (Thilker+, 2007)J/ApJS/173/185 : GALEX ultraviolet atlas of nearby galaxies (Gil de Paz+, 2007)J/AJ/134/2474 : H{alpha} emission-line stars in dwarf galaxies (Massey+, 2007)J/AJ/131/2478 : M31 and M33 UBVRI photometry (Massey+, 2006)J/AJ/133/2393 : UBVRI phot. in 7 Local Group dwarfs galaxies (Massey+, 2007)J/AJ/132/378 : HST and UV photometry of NGC 6822 (Bianchi+, 2006)J/ApJS/155/1 : Phoenix Deep Survey: optical & NIR catalogs (Sullivan+, 2004)J/AJ/126/2840 : BVI CCD photometry of Sextans dSph galaxy (Lee+, 2003)J/AJ/125/1261 : VI photometry of Sextans A Cepheids (Dolphin+, 2003)J/AJ/121/2020 : CTIO and WFPC2 photometry in NGC 6822 (Bianchi+, 2001)J/ApJ/521/577 : HST studies of the WLM globular cluster (Hodge+, 1999)J/AJ/116/2341 : UBVRI photometry in Sextans A (Van Dyk+ 1998)J/AJ/110/2715 : UBV photometry in NGC 6822, M31 and M33 (Massey+ 1995)J/A+AS/71/297 : CCD UBV photometry of stars in Sex A (Aparicio+, 1987)http://dolomiti.pha.jhu.edu/LocalGroup : Results from HST program 11079https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/143/74https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/143/74http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/143/74https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/143/74https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/143/74http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/143/74GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/143/74/table1 (The sample Galaxies)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/143/74/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/143/74/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/143/74/table1?GETtext/xml+votable180.050000true27.77625-44.4447220.005555555555555556Cone search capability for table J/AJ/143/74/table4 (HST photometry catalog)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/143/74/table4?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/143/74/table4?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/143/74/table4?GETtext/xml+votable180.050000true27.71957-44.436370.0055555555555555566/17165 19990 26858 27351 29716 29718 35206 352121.9821045660507152e-19 1.3189343879298211e-18https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/143/74?format=asciiUVdefaultJ/AJ/143/74/table1The sample GalaxiesSimbadNameSimbad column added by the CDSmeta.idcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGalGalaxy namemeta.id;meta.maincharprimaryDist[406/1370] Estimated distance to each galaxykpcpos.distance;pos.galactocentricinte_DistUncertainty on Distkpcstat.errorintr_DistReference for Dist (1)meta.ref;pos.frameintMTypeGalaxy morphological typesrc.morph.typecharMajIsophotal major diameter (25mag/^arcsec^2^)arcminphys.angSizefloatminIsophotal minot diameter (25mag/^arcsec^2^)arcminphys.angSizefloatArea1[5.78/40] Area covered by WFPC2 in arcmin2arcmin**2phys.areafloatArea2[0.1/2.04] Area covered by WFPC2 in kpc2kpc**2phys.angSizefloatVMag[-15.1/-10.1] Absolute visual magnitudemagphys.magAbs;em.opt.VfloatVMag2[-16.0]? Second absolute visual magnitudemagphys.magAbsfloatnullable_RAPositions from SIMBAD database (right ascension part)degpos.eq.ra;meta.main_DEPositions from SIMBAD database (declination part)degpos.eq.dec;meta.mainJ/AJ/143/74/table4HST photometry catalogrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeq[0/26721] Running sequence number (<[BEH2012] {Gal} NNNNN> in Simbad)meta.id;meta.mainintGalParent galaxy namemeta.idcharIAUSource IAU identifier (JHHMMSS.s-DDMMSS)meta.idcharRAJ2000Right Ascension in decimal degrees (J2000)degpos.eq.ra;meta.mainindexedDEJ2000Declination in decimal degrees (J2000)degpos.eq.dec;meta.mainindexedF170W[11.99/23.71]? HST/WFPC2 F170W band Vega magnitude (1)magphot.mag;em.UV.100-200nmfloatnullablee_F170W? Error in F170Wmagstat.errorfloatnullableF225W[7.64/23.58]? HST/WFPC2 F225W band Vega magnitude (1)magphot.mag;em.UV.200-300nmfloatnullablee_F225W? Error in F225Wmagstat.errorfloatnullableF336W[11.34/25.96]? HST/WFPC2 F336W band Vega magnitude (1)magphot.mag;em.opt.Ufloatnullablee_F336W? Error in F336Wmagstat.errorfloatnullableF439W[16.31/26.7]? HST/WFPC2 F439W band Vega magnitude (1)magphot.mag;em.opt.Bfloatnullablee_F439W? Error in F439Wmagstat.errorfloatnullableF555W[16.48/24.59]? HST/WFPC2 F555W band Vega magnitude (1)magphot.mag;em.opt.Vfloatnullablee_F555W? Error in F555Wmagstat.errorfloatnullableF814W[15.43/23.7]? HST/WFPC2 F814W band Vega magnitude (1)magphot.mag;em.opt.Ifloatnullablee_F814W? Error in F814Wmagstat.errorfloatnullableUmag[14.77/25.7]? The U band Vega magnitude (1)magphot.mag;em.opt.UfloatnullableBmag[16.28/26.23]? The B band Vega mag. (1)magphot.mag;em.opt.BfloatnullableVmag[16.47/24.57]? The V band Vega mag. (1)magphot.mag;em.opt.VfloatnullableImag[15.39/23.71]? The I band Vega mag. (1)magphot.mag;em.opt.IfloatnullableSharpHSTphot parameters sharpness of the source (1)stat.fit.paramfloatTp[1/5] HSTphot type of the source, 1=good star (2)src.class.starGalaxyintFr[1/15] The visit number from Table 2 (3)obs.fieldintCh[0/3] WFPC2 detector: 0=PC, 1=WF2, 2=WP3, 3=WF4meta.noteint