J/ApJ/804/71ivo://CDS.VizieR/J/ApJ/804/71doi:10.26093/cds/vizier.18040071CDSLarsen S.S.Baumgardt H.Bastian N.Brodie J.P.Grundahl F.Strader J.2015-10-16T15:10:16Z2015-09-23T08:38:23ZCDS support team

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

cds-question@unistra.frglobular-star-clustershst-photometryWe examine the radial distributions of stellar populations in the globular cluster (GC) M15, using Hubble Space Telescope/Wide Field Camera 3 (WFC3) photometry of red giants in the nitrogen-sensitive F343N-F555W color. Surprisingly, we find that giants with "primordial" composition (i.e., N abundances similar to those in field stars) are the most centrally concentrated within the WFC3 field. We then combine our WFC3 data with Sloan Digital Sky Survey u,g photometry and find that the trend reverses for radii >~1' (3pc) where the ratio of primordial to N-enhanced giants increases outward, as already found by Lardo et al. (2011A&A...525A.114L). The ratio of primordial to enriched stars thus has a U-shaped dependency on radius with a minimum near the half-light radius. N-body simulations show that mass segregation might produce a trend resembling the observed one, but only if the N-enhanced giants are ~0.25M_{sun}_ less massive than the primordial giants, which requires extreme He enhancement (Y>~0.40). However, such a large difference in Y is incompatible with the negligible optical color differences between primordial and enriched giants, which suggest {Delta}Y<~0.03 and thus a difference in turn-off mass of {Delta}M<~0.04M_{sun}_ between the different populations. The radial trends in M15 are thus unlikely to be of dynamical origin and presumably reflect initial conditions, a result that challenges all current GC formation scenarios. We note that population gradients in the central regions of GCs remain poorly investigated and may show a more diverse behavior than hitherto thought.2015ApJ...804...71Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/804/71CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toB/hst : HST Archived Exposures Catalog (STScI, 2007)VII/202 : Globular Clusters in the Milky Way (Harris, 1997)J/ApJ/797/15 : HST/WFC3 obs. in 4 metal-poor GCs of Fornax (Larsen+, 2014)J/PASP/126/733 : BVI photometry of M15 stars (Feuillet+, 2014)J/MNRAS/423/2260 : VI photometry of M15 core (Diaz-Sanchez+, 2012)J/A+A/534/A9 : Synthetic spectra of galactic GCs (Sbordone+, 2011)J/AJ/141/175 : Abundances in M15 RGB/RHB stars (Sobeck+, 2011)J/A+A/524/A44 : CN and CH line strengths in 12 globulars (Pancino+, 2010)J/A+A/505/117 : Abundances of red giants in 15 GCs (Carretta+, 2009)J/A+A/486/437 : CN and CH line strengths in 8 Galactic GlCl (Kayser+, 2008)J/AJ/130/1177 : C and N abundances for M15 stars (Cohen+, 2005)J/A+A/354/169 : Metal-poor field stars abundances (Gratton+, 2000)J/A+AS/139/393 : Young Massive Star Clusters. II. (Larsen, 1999)J/AJ/107/1745 : HST UVI photometry of M15. II. (Yanny+, 1994)J/AJ/106/154 : HST Observations in inner region of M15 (Ferraro+ 1993)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/804/71https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/804/71http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/804/71https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/804/71https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/804/71http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/804/71GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/804/71/table1 (*ALLFRAME photometry of M15)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/804/71/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/804/71/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/804/71/table1?GETtext/xml+votable180.050000true322.5082461112.154236110.0055555555555555566/124052.238682544986967e-19 5.993397539078468e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/804/71?format=asciiOpticaldefaultJ/ApJ/804/71/table1*ALLFRAME photometry of M15ID[102/569880] Source identifiermeta.id;meta.mainintprimaryXpixX pixel coordinate on drizzled CCD framepixpos.cartesian.x;instr.detfloatYpixY pixel coordinate on drizzled CCD framepixpos.cartesian.y;instr.detfloatRAJ2000Right Ascension; decimal degrees (J2000)degpos.eq.ra;meta.mainDEJ2000Declination; decimal degrees (J2000)degpos.eq.dec;meta.mainR[4/130] Projected distance from cluster centerarcsecpos.angDistancefloatF343N[15.9/20.8] HST/WFC3 F343N filter ALLFRAME STMAG magnitudemagphot.mag;em.opt.Ufloate_F343N[0.005/0.3] Error in F343Nmagstat.errorfloatF555W[14.9/19] HST/WFC3 F555W filter ALLFRAME STMAG magnitudemagphot.mag;em.opt.Vfloate_F555W[0.004/0.2] Error in F555Wmagstat.errorfloatF814W[15/20.5] HST/WFC3 F814W filter ALLFRAME STMAG magnitudemagphot.mag;em.opt.Ifloate_F814W[0.006/0.5] Error in F814Wmagstat.errorfloat