A chemical close-up of the main body of the Sagittarius dwarf galaxy

¹ Section of Astrophysics, Astronomy and Mechanics, Physics Department, National and Kapodistrian University of Athens, Panepistimiopolis, 15784 Zografos, Athens, Greece
² Dipartimento di Fisica e Astronomia “Augusto Righi”, Alma Mater Studiorum, Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
³ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

^★ Corresponding author.

Received: 7 March 2025
Accepted: 1 June 2025

Abstract

We present the chemical composition of a sample of 37 red giant branch (RGB) stars belonging to the main body of the remnant of the Sagittarius (Sgr) dwarf spheroidal galaxy. All stars were observed with the FLAMES-UVES high-resolution spectrograph. Twenty-three new targets were selected along the blue side of the RGB of Sgr, but outside the galaxy stellar nucleus, in order to avoid contamination by the stars of the metal-poor globular cluster M54. Additionally, we re-analysed archival spectra of 14 targets located on the red RGB. For this sample, we derive the abundances of 21 chemical species (from oxygen to europium) representing different nucleosynthetic sites. The sample covers a large range of metallicities, from [Fe/H]~-2 to ~-0.4 dex, and we can identify the transition between the enrichment phases dominated by core-collapse and Type Ia supernovae. The observed [α/Fe] trend suggests a knee occurring at [Fe/H]~ −1.5/−1.3 dex, compatible with the rather low star formation efficiency of Sgr. At lower [Fe/H], Sgr stars exhibit a chemical composition compatible with Milky Way stars of similar [Fe/H]. The only relevant exceptions are [Mn/Fe], [Zn/Fe], and [Eu/Fe]. Instead, at [Fe/H] higher than −1.5/−1.3 dex, the chemical pattern of Sgr significantly deviates from that of the Milky Way for almost all the elements analysed in this study. Some of the abundance patterns reveal a lower contribution by very massive stars exploding as hypernovae (e.g. [Mn/Fe], [Zn/Fe]), a higher contribution by sub-Chandrasekhar progenitors of Type Ia supernovae (e.g. [Ni/Fe]), and a high production efficiency of rapid neutron-capture elements ([Eu/Fe]).