A Search for Nitrogen‐enhanced Metal‐poor Stars

Abstract

Theoretical models of very metal-poor intermediate-mass asymptoticgiant branch (AGB) stars predict a large overabundance of primarynitrogen. The very metal-poor, carbon-enhanced, s-process-richstars, which are thought to be the polluted companions of now extinctAGB stars, provide direct tests of the predictions of these models.Recent studies of the carbon and nitrogen abundances in metal-poorstars have focused on the most carbon-rich stars, leading to apotential selection bias against stars that have been polluted byAGB stars that produced large amounts of nitrogen and hence havesmall [C/N] ratios. We call these stars nitrogen-enhanced metal-poor(NEMP) stars and define them as having [N/Fe]>+0.5 and [C/N]