NGC 2808 AGB and RGB stars Na abundance

While second-population stars, identified by their Na overabundance, have been found from the main sequence turnoff up to the tip of the red giant branch in various Galactic GCs, asymptotic giant branch stars have rarely been targeted. Here we present the results of our high-resolution spectroscopic study of a sample of AGB and RGB stars in the Galactic globular cluster NGC 2808.

We derived accurate Na abundances for 31 AGB and 40 RGB stars in this cluster. Comparable Na abundance dispersions are found for our AGB and RGB samples, and we conclude that NGC 2808 has Na-rich second-population AGB stars, which turn out to be even more numerous - in relative terms - than their Na-poor counterparts (on the AGB) and the Na-rich stars on the RGB.