Characterizing the Chemistry of the Milky Way Stellar Halo: Detailed Chemical Analysis of a Metal-Poor Stellar Stream

TL;DR

This study provides a detailed chemical analysis of a metal-poor stellar stream in the Milky Way halo, revealing its homogeneous composition and implications for galaxy formation from accreted systems.

Contribution

It offers the first comprehensive abundance analysis of a stellar stream, showing chemical homogeneity and specific nucleosynthetic signatures, advancing understanding of halo assembly.

Findings

Stream members are chemically homogeneous despite metallicity variation.

Minimal evolution observed in alpha and Fe-group elements across metallicities.

Enrichment primarily from rapid neutron-capture process, no slow process evidence.

Abstract

We present the results of a detailed abundance analysis of one of the confirmed building blocks of the Milky Way stellar halo, a kinematically-coherent metal-poor stellar stream. We have obtained high resolution and high S/N spectra of 12 probable stream members using the MIKE spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the 2dCoude spectrograph on the Smith Telescope at McDonald Observatory. We have derived abundances or upper limits for 51 species of 46 elements in each of these stars. The stream members show a range of metallicity (-3.4 < [Fe/H] < -1.5) but are otherwise chemically homogeneous, with the same star-to-star dispersion in [X/Fe] as the rest of the halo. This implies that, in principle, a significant fraction of the Milky Way stellar halo could have formed from accreted systems like the stream. The stream stars show minimal evolution in the alpha or Fe-group elements over the range of metallicity. This stream is enriched with material produced by the main and weak components of the rapid neutron-capture process and shows no evidence for enrichment by the slow neutron-capture process.