Searches for the Most Metal-Poor Candidates from SDSS and SEGUE

TL;DR

This paper describes the identification of over 8,000 very metal-poor stars from SDSS and SEGUE data, highlighting the potential to find more and discussing implications for understanding the Milky Way's halo structure.

Contribution

It presents a large sample of metal-poor stars identified through medium-resolution spectroscopy and photometry, advancing the search for the most metal-poor stars in the galaxy.

Findings

Over 8,000 stars with [Fe/H] <= -2.0 identified

Expected to find over 10,000 such stars after SEGUE completion

Confirmation of inner/outer halo dichotomy in the Milky Way

Abstract

We report on efforts to identify large samples of very and extremely metal-poor stars based on medium-resolution spectroscopy and ugriz photometry obtained during the course of the Sloan Digital Sky Survey (SDSS), and its extension, SDSS-II, which includes the program SEGUE: Sloan Extension for Galactic Understanding and Exploration. To date, over 8000 stars with [Fe/H] <= -2.0 and effective temperatures in the range 4500K < T_eff < 7000K have been found, with the expected numbers in this temperature range to be well over 10,000 once SEGUE is completed. The numbers roughly double when one includes warmer blue stragglers and Blue Horizontal-Branch (BHB) stars in these counts. We show the observed low-metallicity tails of the Metallicity Distribution Functions for the cooler SDSS/SEGUE stars obtained thus far. We also comment on the confirmation of an inner/outer halo dichotomy in the Milky Way, and on how this realization may be used to direct searches for even more metal-poor stars in the near future.