Browsing by Author "Renzini, A"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    The metal content of the bulge globular cluster NGC 6528
    (2004) Zoccali, A; Barbuy, B; Hill, V; Ortolani, S; Renzini, A; Bica, E; Momany, Y; Pasquini, L; Minniti, D; Rich, RM
    High resolution spectra of five stars in the bulge globular cluster NGC 6528 were obtained at the 8m VLT UT2-Kueyen telescope with the UVES spectrograph. Out of the five stars, two of them showed evidence of binarity. The target stars belong to the horizontal and red giant branch stages, at 4000 < T-eff < 4800 K. Multiband V, I, J, H, K-s, photometry was used to derive initial effective temperatures and gravities. The main purpose of this study is the determination of metallicity and elemental ratios for this template bulge cluster, as a basis for the fundamental calibration of metal-rich populations. The present analysis provides a metallicity [Fe/H] = -0.1 +/- 0.2 and the alpha-elements O, Mg and Si, show [alpha/Fe] approximate to+0.1, whereas Ca and Ti are around the solar value or below, resulting in an overall metallicity Z approximate to Z(.).
  • No Thumbnail Available
    Item
    The stellar content of the bulge of M31
    (2003) Stephens, AW; Frogel, JA; DePoy, DL; Freedman, W; Gallart, C; Jablonka, P; Renzini, A; Rich, RM; Davies, R
    We analyze the stellar populations present in M31 by using nine sets of adjacent Hubble Space Telescope NICMOS camera 1 and 2 fields with galactocentric distances ranging from 2' to 20'. These infrared observations provide some of the highest spatial resolution measurements of M31 to date; our data place tight constraints on the maximum luminosities of stars in the bulge of M31. The tip of the red giant branch is clearly visible at M-bol similar to -3.8, and the tip of the asymptotic giant branch (AGB) extends to M-bol similar to -5. This AGB peak luminosity is significantly fainter than previously claimed; through direct comparisons and simulations we show that previous measurements were affected by image blending. We do observe field-to-field variations in the luminosity functions, but simulations show that these differences can be produced by blending in the higher surface brightness fields. We conclude that the red giant branch of the bulge of M31 is not measurably different from that of the bulge of the Milky Way. We also find an unusually high number of bright bluish stars (7.3 arcmin(-2)), which appear to be Galactic foreground stars.
  • No Thumbnail Available
    Item
    VLT-UVES analysis of two giants in the bulge metal-poor globular cluster HP-1 - Analysis of two giants in HP-1
    (2006) Barbuy, B; Zoccali, M; Ortolani, S; Momany, Y; Minniti, D; Hill, V; Renzini, A; Rich, RM; Bica, E; Pasquini, L; Yadav, RKS
    Context. Metal-poor globular clusters in the bulge are important tracers of early chemical evolution. HP-1 is among the six metal-poor clusters within 5. of the Galactic center, and could be the one closest to the center