J/AJ/110/1649ivo://CDS.VizieR/J/AJ/110/1649doi:10.26093/cds/vizier.51101649CDSMighell K.J.Rich R.M.2023-04-06T16:50:18Z1997-12-09T20:29:04ZCDS support team

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

cds-question@unistra.frstellar-populationsphotometryWe have studied the stellar populations near the nucleus of the nearby spiral galaxy M33 using archival observations of the Hubble Space Telescope Planetary Camera in the F555W and F785LP passbands. The I vs (V-I) color-magnitude diagram reveals a young stellar population with a blue main sequence and red supergiants, and stars in a blue loop that are Cepheid candidates. An old red giant branch is clearly visible, with a break at I=20.7mag which is, within the observational errors, identical to the giant branch termination point of the Mould & Kristian (1986ApJ...305..591M) halo field. However, red giants are seen up to I=19.5mag, and many bright red giants are undetected in the V band. We find evidence for a wide abundance spread of at least 1.5dex from metal-poor (~M15) to metal-rich (>=47Tucanae) in the Population II stars, in sharp contrast to the M33 halo field of Mould & Kristian (1986ApJ...305..591M) which is metal-poor (~M92) with a narrow abundance range. We show that the various stellar populations have different spatial distributions. The Population II stars are more centrally concentrated than the Population I stars. The red giants brighter than I=20.7 (the termination point for a Galactic globular cluster giant branch) are found to be more centrally concentrated than the (presumably) old red giants. The most-centrally concentrated bright Population II giants are probably associated with the many bright red giants that are undetected in the V band. These infrared-bright giants were probably created in an intermediate-age burst of star formation that took place well after the formation of the oldest halo stars but long before the recent burst of star formation seen in nearby OB associations. This stellar population probably corresponds to the bulge identified in the infrared H band by Minniti et al. (1993ApJ...410L..79M).1995AJ....110.1649Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/110/1649CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/AJ/121/861 : BVI photometry of central part of M33 (Macri+, 2001)J/AJ/121/870 : Variables in the central part of M33 BVI phot. (Macri+, 2001)J/A+A/366/498 : HST VI photometry of M33 star clusters (Chandar+, 2001)J/AJ/110/2715 : UBV photometry in NGC 6822, M31 and M33 (Massey+ 1995)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/110/1649https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/110/1649http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/110/1649https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/110/1649https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/110/1649http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/110/1649GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/AJ/110/1649/table1Photometry of stars near the nucleus of M33recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIDCoded identification (1)meta.codelongF785LPF785LP (i) magnitudemagphot.mag;em.opt.Ifloate_F785LPF785LP photometric errormagstat.errorfloatF555WF555W (v) magnitudemagphot.mag;em.opt.Vfloate_F555WF555W photometric errormagstat.errorfloatImag[]? I magnitudemagphot.mag;em.opt.IfloatV-IV-I colormagphot.color;em.opt.V;em.opt.IfloatdRARight ascension (J2000) offset (2)arcsecpos.eq.ra;arith.difffloatdDEDeclination (J2000) offset (2)arcsecpos.eq.dec;arith.difffloatClassPhotometric measurement class (3)meta.note;photint