A Nitrogen-Enhanced Metal-Poor star discovered in the globular cluster ESO280-SC06

TL;DR

This paper reports the discovery of the only nitrogen-enhanced metal-poor star in a globular cluster, providing insights into stellar evolution and cluster properties.

Contribution

It is the first identification of a nitrogen-enhanced metal-poor star in a globular cluster and includes the discovery of horizontal branch members and an updated orbital analysis.

Findings

Discovery of a nitrogen-enhanced star with [N/Fe]>+2.5 in ESO280-SC06

Identification of the first horizontal branch members in the cluster

Revised cluster distance of 20.6 kpc and unchanged orbital properties

Abstract

We report the discovery of the only very nitrogen-enhanced metal-poor star known in a Galactic globular cluster. This star, in the very metal-poor cluster ESO280-SC06, has [N/Fe]$>+2.5$, while the other stars in the cluster show no obvious enhancement in nitrogen. Around 80 NEMP stars are known in the field, and their abundance patterns are believed to reflect mass transfer from a binary companion in the asymptotic giant branch phase. The dense environment of globular clusters is detrimental to the long-term survival of binary systems, resulting in a low observed binary fraction among red giants and the near absence of NEMP stars. We also identify the first known horizontal branch members of ESO280-SC06, which allow for a much better constraint on its distance. We calculate an updated orbit for the cluster based on our revised distance of $20.6 \pm 0.5~$kpc, and find no significant change to its orbital properties.