2001/02/28 by Eugenio Carretta, Judith G. Cohen, Raffaele G. Gratton +1 · 14 citations
Physics and Astronomy · Social Sciences · #Abundance (ecology) #Astronomy and Astrophysical Research #Bulge #Educational Leadership and Practices #Globular cluster #Hubble sequence #Metallicity #Open cluster #Spectral line #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/322116
accepted for publication in the September 2001 issue of The Astronomical Journal; 3 new figures and updated results and calibrations
arxiv created 2001/06/12 · openalex publication_date 2001/09/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present the results of the first analysis of high-dispersion spectra of four red horizontal-branch stars in the metal-rich globular cluster NGC 6528, located in Baade's window. We find that the mean [Fe/H] for NGC 6528 is +0.07 ± 0.01 dex (error of the mean), with a star-to-star scatter of σ = 0.02 dex (four stars), although the total error is likely to be larger (∼0.1 dex) because of systematic errors related to the effective temperature scale and to model atmospheres. This metallicity is somewhat larger than both the mean abundance in the galactic bulge found by McWilliam & Rich (1994) and that found in our previous paper for NGC 6553. However, we find that the spectra of clump stars in NGC 6528 and 6553 are very similar each other, the slightly different metal abundances found being possibly due to the different atmospheric parameters adopted in the two analyses. Since the present analysis is based on higher quality material, we propose to revise our previous published metal abundance for NGC 6553 to [Fe/H] = -0.06 ± 0.15. For NGC 6528, we find excesses for the α-process elements Si and Ca ([Si/Fe] = +0.4 and [Ca/Fe] = +0.2), whereas Mn is found to be underabundant ([Mn/Fe] = -0.4). We find a solar abundance of O; however, this is somewhat uncertain because of the dependence of the O abundance on the adopted atmospheric parameters and the coupling between C and O abundances in these cool, metal-rich stars. Finally, we find large Na excesses ([Na/Fe] ∼ +0.4) in all stars examined.