general rise in the global CEMP frequency at low metallicity is likely due to the transition from the inner-halo to the outer-halo stellar populations with declining metallicity and increasing distance from the plane.
author:
- |
    Young Sun Lee, Timothy C. Beers, Thomas Masseron, Bertrand Plez, Constance M. Rockosi,\
    Jennifer Sobeck, Brian Yanny, Sara Lucatello, Thirupathi Sivarani,\
    Vinicius M. Placco, and Daniela Carollo\
title: |
    Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I.\
    Carbon Abundance Estimation and Frequency of CEMP Stars
---

Introduction
============

The chemical abundance ratios of very metal-poor (VMP; \[Fe/H\]$\leq -2.0$) stars in the Milky Way provide vital clues to the early chemical evolution and initial mass function (IMF) of their progenitors, which are likely to have been among the first generations of stars formed in the universe.

Given this importance, there have been increasingly ambitious efforts carried out to identify metal-poor candidates with large-scale surveys of the stellar populations of the Milky Way. The early HK survey (Beers et al. 1985, 1992) and the Hamburg/ESO Survey (HES; Wisotzki et al. 1996; Christlieb 2003; Christlieb et al. 2001, 2008) collectively identified several thousand VMP stars (Beers & Christlieb 2005). In recent years, this number has been dramatically increased by 