The [Fe/H], [C/Fe], and [alpha/Fe] distributions of the Bootes I Dwarf Spheroidal Galaxy

TL;DR

This study analyzes the chemical composition of 25 stars in the Bootes I dwarf galaxy, revealing a wide metallicity range, including extremely metal-poor stars, and comparing its chemical evolution to models and the Galactic halo.

Contribution

First detailed low-resolution spectral abundance analysis of stars in Bootes I, including discovery of an extremely metal-poor star and comparison with chemical evolution models.

Findings

Wide metallicity spread of 2.1 dex in [Fe/H]

Discovery of a star with [Fe/H]=-3.8, one of the most metal-poor in a dSph

Chemical abundance patterns similar to Galactic halo stars

Abstract

We present the results of a low-resolution spectral abundance study of 25 stars in the Bootes I dwarf spheroidal (dSph) galaxy. The data were obtained with the LRIS instrument at Keck Observatory, and allow us to measure [Fe/H], [C/Fe], and [alpha/Fe] for each star. We find both a large spread in metallicity (2.1 dex in [Fe/H]) as well as the low average metallicity in this system, <[Fe/H]>=-2.59, matching previous estimates. This sample includes a newly discovered extremely metal-poor star, with [Fe/H]=-3.8, that is one of the most metal-poor stars yet found in a dSph. We compare the metallicity distribution function of Bootes I to analytic chemical evolution models. While the metallicity distribution function of Bootes I is best fit by an Extra Gas chemical evolution model, leaky-box models also provide reasonable fits. We also find that the [alpha/Fe] distribution and the carbon-enhanced metal-poor fraction of our sample (12%) are reasonable matches to Galactic halo star samples in the same metallicity range, indicating that at these low metallicities, systems like the Bootes I ultra-faint dSph could have been contributors to the Galactic halo.