Carbon-enhanced metal-poor stars in the SDSS-APOGEE database

TL;DR

This study identifies new carbon-enhanced metal-poor stars in the SDSS-APOGEE database, expanding the catalog of such stars and analyzing their chemical properties to understand their origins and classifications.

Contribution

The paper reports six new CEMP stars and seven candidates from APOGEE DR12, providing chemical compositions and initial insights into their binary status and sub-classification challenges.

Findings

Six new CEMP stars identified

Most are not CEMP-s stars based on radial velocities

One star may be in a binary system

Abstract

We identify six new CEMP stars ([C/Fe]>+0.7 and [Fe/H]< -1.8) and another seven likely candidates within the APOGEE database following Data Release 12. These stars have chemical compositions typical of metal-poor halo stars, e.g., mean [$\alpha$/Fe] = +0.24$\pm$0.24, based on the ASPCAP pipeline results. A lack of heavy element spectral lines impedes further sub-classification of these CEMP stars, however, based on radial velocity scatter, we predict most are not CEMP-s stars which are typically found in binary systems. Only one object, 2M15312547+4220551, may be in a binary since it exhibits a scatter in its radial velocity of 1.7 $\pm$0.6 km s$^{-1}$ based on three visits over a 25.98 day baseline. Optical observations are now necessary to confirm the stellar parameters and low metallicities of these stars, to determine the heavy-element abundance ratios and improve the precision in the derived abundances, and to examine their CEMP sub-classifications.