S⁵: The Destruction of a Bright Dwarf Galaxy as Revealed by the Chemistry of the Indus Stellar Stream

The recently discovered Indus stellar stream exhibits a diverse chemical signature compared to what is found for most other streams due to the abundances of two outlier stars, Indus_0 and Indus_13. Indus_13 exhibits an extreme enhancement in rapid neutron-capture (r-)process elements with [Eu/Fe] = + 1.81. It thus provides direct evidence of the accreted nature of r-process-enhanced stars. In this paper we present a detailed chemical analysis of the neutron-capture elements in Indus_13, revealing the star to be slightly actinide poor. The other outlier, Indus_0, displays a globular cluster-like signature with high N, Na, and Al abundances, while the rest of the Indus stars show abundances compatible with a dwarf galaxy origin. Hence, Indus_0 provides the first chemical evidence of a fully disrupted dwarf containing a globular cluster. We use the chemical signature of the Indus stars to discuss the nature of the stream progenitor which was likely a chemically evolved system, with a mass somewhere in the range from Ursa Minor to Fornax.