Chemical abundances of hydrostatic and explosive alpha-elements in Sagittarius stream stars

TL;DR

This study investigates the chemical abundances of alpha-elements in Sagittarius stream stars, revealing differences from Milky Way stars and insights into the galaxy's initial mass function and chemical evolution.

Contribution

It provides the first detailed analysis of hydrostatic and explosive alpha-elements in Sagittarius stream stars, linking their chemical properties to the galaxy's star formation history.

Findings

Sgr stream stars have lower [Fe/H] than the core.

Hydrostatic elements are more depleted than explosive elements compared to MW stars.

HEx ratio trends suggest a lack of the most massive stars in Sgr's IMF.

Abstract

We analyze chemical abundances of stars in the Sagittarius (Sgr) tidal stream using high-resolution Gemini+GRACES spectra of 42 members of the highest surface brightness portions of both the trailing and leading arms. Targets were chosen using a 2MASS+WISE color-color selection, combined with LAMOST radial velocities. In this study, we analyze [Fe/H] and alpha-elements produced by both hydrostatic (O, Mg) and explosive (Si, Ca, Ti) nucleosynthetic processes. The average [Fe/H] for our Sgr stream stars is lower than that for stars in the Sgr core, and stars in the trailing and leading arms show systematic differences in [Fe/H]. Both hydrostatic and explosive elements are depleted relative to Milky Way (MW) disk and halo stars, with a larger gap between the MW trend and Sgr stars for the hydrostatic elements. Chemical abundances of Sgr stream stars show similar patterns to those measured in the core of the Sgr dSph. We explore the ratio of hydrostatic to explosive alpha-elements [$\alpha_{\rm h/ex}$] (which we refer to as the "HEx ratio"). Our observed HEx ratio trends for Sgr debris are deficient relative to MW stars. Via simple chemical evolution modeling, we show that these HEx ratio patterns are consistent with a Sgr IMF that lacks the most massive stars. This study provides a link between the chemical properties in the intact Sgr core and the significant portion of the Sgr system's luminosity that is estimated to currently reside in the streams.