Surprising Metallicity of a Newly Discovered M79 Post-AGB Star

TL;DR

This paper presents a detailed chemical analysis of a newly discovered post-AGB star in M79, revealing unexpected metallicity levels that differ from the cluster’s red giants, challenging previous assumptions about stellar evolution in this cluster.

Contribution

It provides the first detailed chemical composition of a post-AGB star in M79, highlighting a surprising metallicity discrepancy with cluster red giants.

Findings

Star's iron abundance is 0.6 dex lower than cluster red giants.

Elemental abundances show high oxygen and alpha-process enhancement.

The metallicity discrepancy challenges existing stellar evolution models.

Abstract

A detailed chemical composition analysis based on a high-resolution (R=35,000) CCD spectrum is presented for a newly discovered post-AGB star in the globular cluster M79 for the first time. The elemental abundance results of M79 Post-AGB star are found to be [C/Fe]=-0.7, [O/Fe]=+1.4, [alpha- process/Fe]=0.5, and [s-process/Fe]=-0.1. The surprising result is that the iron abundance of the star is apparently about 0.6 dex less than that of the cluster's red giants as reported by published studies including a recent high-resolution spectroscopic analysis by Carretta and colleagues.