The Age and Metallicity of the Bootes I System

TL;DR

This study uses Washington photometry to analyze the stellar populations of the Bootes I dwarf galaxy, revealing its age, metallicity, and membership with improved star separation techniques.

Contribution

It demonstrates the effectiveness of Washington filters over Sloan filters in identifying metal-poor stars and provides detailed age and metallicity estimates for Bootes I.

Findings

Approximately 40% of observed objects are non-members.

The galaxy's main-sequence turn-off suggests an age of about 14.1 Gyr.

The mean iron abundance is [Fe/H] = -2.1 +/- 0.4.

Abstract

We present Washington photometry of a field central to the Bootes I dwarf spheroidal galaxy, which was discovered as a stellar overdensity in the Sloan Digital Sky Survey (DR5). We show that the Washington filters are much more effective than the Sloan filters in separating the metal-poor turn-off stars in the dwarf galaxy from the foreground stars. We detect 165 objects in the field, and statistically determine that just over 40% of the objects are non-members. Our statistical analysis mostly agrees with radial velocity measurements of the brighter stars. We find that that there is a distinct main-sequence turn-off and subgiant branch, where there is some evidence of a spread in chemical abundance. Any evidence of an age spread is limited to a few billion years. The brightest 7 Bootes I members give a (photometric-color derived) weighted mean iron-abundance of [Fe/H]=-2.1+/-0.4, and the best-fit isochrone is the 14.1 Gyr, Z=0.0002 model, with DM=19.11 and E(B-V)=0.02.