期刊
ASTRONOMY & ASTROPHYSICS
卷 605, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201730707
关键词
galaxies: dwarf; Local Group; galaxies: stellar content; stars: abundances
资金
- W. M. Keck Foundation
- National Aeronautics and Space Administration
- team The Formation and Evolution of the Galactic Halo
We present iron, magnesium, calcium, and titanium abundances for 235 stars in the central region of the Sagittarius dwarf spheroidal galaxy (within 9.0' similar or equal to 70 pc from the centre) from medium-resolution Keck/Deep Imaging Multi-Object Spectrograph spectra. All the considered stars belong to the massive globular cluster M 54 or to the central nucleus of the galaxy (Sgr, N). In particular we provide abundances for 109 stars with [Fe/H] >= -1.0, more than doubling the available sample of spectroscopic metallicity and alpha-elements abundance estimates for Sgr dSph stars in this metallicity regime. We find for the first time a metallicity gradient in the Sgr, N population, whose peak iron abundance goes from [Fe/H] = -0.38 for R <= 2.5' to [Fe/H] = -0.57 for 5.0 < R <= 9.0'. On the other hand, the trends of [Mg/Fe], [Ca/Fe], and [Ti/Fe] with [Fe/H] are the same over the entire region explored by our study. We reproduce the observed chemical patterns of the Sagittarius dwarf spheroidal as a whole with a chemical evolution model which implies that a high mass progenitor (M-DM = 6 x 10(10) M-circle dot) and a significant event of mass-stripping occurred a few Gyr ago, presumably starting at the first peri-Galactic passage after infall.
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