Investigating APOKASC Red Giant Stars with Abnormal Carbon to Nitrogen Ratios

Abstract

The success of galactic archaeology and the reconstruction of the formation history of our galaxy critically relies on precise ages for large populations of stars. For evolved stars in the red clump and red giant branch, the carbon to nitrogen ratio ([C/N]) has recently been identified as a powerful diagnostic of mass and age that can be applied to stellar samples from spectroscopic surveys such as SDSS/APOGEE. Here, we show that at least 10\% of red clump stars and %$\approx 10\%$ of red giant branch stars deviate from the standard relationship between [C/N] and mass. {We use the APOGEE-\kepler\ (APOKASC) overlap sample to show that binary interactions are %the majority contributors to these responsible for the majority of these outliers and that stars with %any indicators of current or previous binarity should be excluded from galactic archaeology analyses that rely on [C/N] abundances to infer stellar masses. We also show that the %standard DR14 APOGEE analysis overestimates the surface gravities for even moderately rotating giants (vsini$>2$ km/s)}