Homogeneity in the early chemical evolution of the Sextans dwarf spheroidal galaxy
R. Lucchesi, C. Lardo, F. Primas, P. Jablonka, P. North, G. Battaglia, E. Starkenburg, V. Hill, M. Irwin, P. Francois, M. Shetrone, E. Tolstoy, K. Venn
Abstract
We present the high-resolution spectroscopic analysis of two new extremely metal-poor star (EMPS) candidates in the dwarf spheroidal galaxy Sextans. These targets were preselected from medium-resolution spectra centered around the Ca II triplet in the near-infrared and were followed-up at higher resolution with VLT/UVES. We confirm their low metallicities with [Fe/H] = −2.95 and [Fe/H] = −3.01, which place them among the most metal-poor stars known in Sextans. The abundances of 18 elements, including C, Na, the α , Fe-peak, and neutron-capture elements, are determined. In particular, we present the first unambiguous detection of Zn in a classical dwarf at extremely low metallicity. Previous indications were made of a large scatter in the abundance ratios of the Sextans stellar population around [Fe/H] ∼ − 3 when compared to other galaxies, particularly with very low observed [ α /Fe] ratios. We took the opportunity of reanalyzing the full sample of EMPS in Sextans and find a [ α /Fe] Milky Way-like plateau and a ∼0.2 dex dispersion at fixed metallicity.