Homogeneity in the early chemical evolution of the Sextans dwarf spheroidal galaxy^⋆

¹ European Southern Observatory, Karl-Schwarzschild-str. 2, 85748 Garching bei München, Germany
e-mail: romain.lucchesi@epfl.ch
² Physics Institute, Laboratoire d’astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire, 1290 Versoix, Switzerland
³ GEPI, Observatoire de Paris, CNRS, Université de Paris Diderot, 92195 Meudon Cedex, France
⁴ Instituto de Astrofísica de Canarias (IAC), Calle Via Láctea, s/n, 38205 San Cristóbal de la Laguna, Tenerife, Spain
⁵ Departamento de Astrofísica, Universidad de La Laguna, 38206 San Cristóbal de la Laguna, Tenerife, Spain
⁶ Leibniz-Institut fur Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁷ Laboratoire Lagrange, Université de Nice Sophia-Antipolis, Observatoire de la Côte d’Azur, France
⁸ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁹ McDonald Observatory, University of Texas at Austin, Fort David, TX, USA
¹⁰ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
¹¹ Department of Physics and Astronomy, University of Victoria, PO Box 3055, STN CSC, Victoria, BC V8W 3P6, Canada

Received: 20 January 2020
Accepted: 20 August 2020

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.