摘要：We present iron, magnesium, calcium, and titanium abundances for 235 stars in the central region of the Sagittarius dwarf spheroidal galaxy (within 9.0′ ≃ 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 α-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
