The Pristine Inner Galaxy Survey (PIGS)

IX. The largest detailed chemical analysis of very metal-poor stars in the Sagittarius dwarf galaxy

¹ Department of Physics and Astronomy, University of Victoria, PO Box 3055 STN CSC, Victoria, BC V8W 3P6 Canada
² Instituto de Estudios Astrofísicos, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
³ Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
⁴ Universidad de La Laguna, Departamento de Astrofísica, 38206 La Laguna, Tenerife, Spain
⁵ Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuna Mackenna 4860, Santiago, Chile
⁶ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA UK
⁷ Department of Astronomy & Astrophysics, University of Toronto, Toronto, ON M5S 3H4 Canada
⁸ Université Cote d’Azur, Observatoire de la Cote d’Azur, CNRS, Laboratoire Lagrange, Nice, France
⁹ Laboratoire d’astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire, CH-1290 Versoix, Switzerland
¹⁰ GEPI, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, F-92195 Meudon, France
¹¹ Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, F-67000 Strasbourg, France
¹² Max-Planck-Institut fur Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
¹³ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
¹⁴ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands

Received: 29 April 2024
Accepted: 15 June 2024

Abstract

The most metal-poor stars provide valuable insights into the early chemical enrichment history of a system, carrying the chemical imprints of the first generations of supernovae. The most metal-poor region of the Sagittarius dwarf galaxy remains inadequately observed and characterised. To date, only ∼4 stars with [Fe/H] < −2.0 have been chemically analysed with high-resolution spectroscopy. In this study, we present the most extensive chemical abundance analysis of 12 low-metallicity stars with metallicities down to [Fe/H] = −3.26 and located in the main body of Sagittarius. These targets, selected from the Pristine Inner Galaxy Survey, were observed using the MIKE high-resolution spectrograph at the Magellan-Clay telescope, which allowed us to measure up to 17 chemical species. The chemical composition of these stars reflects the imprint of a variety of type II supernovae (SNe II). A combination of low- to intermediate-mass high-energy SNe and hypernovae (∼10 − 70 M_⊙) is required to account for the abundance patterns of the lighter elements up to the Fe-peak. The trend of the heavy elements suggests the involvement of compact binary merger events and fast-rotating (up to ∼300 km s⁻¹) intermediate-mass to massive metal-poor stars (∼25 − 120 M_⊙) that are the sources of rapid and slow processes, respectively. Additionally, asymptotic giant branch stars contribute to a wide dispersion of [Ba/Mg] and [Ba/Eu]. The absence of an α−knee in our data indicates that type Ia supernovae did not contribute in the very metal-poor region ([Fe/H] ≤ −2.0). However, they might have started to pollute the interstellar medium at [Fe/H] > −2.0, given the relatively low [Co/Fe] in this metallicity region.