# GALEX J184559.8-413827: a new extreme helium star identified using SALT

## TL;DR

This paper reports the discovery and detailed analysis of GALEX J184559.8-413827, the first extreme helium star found in nearly four decades, providing insights into its properties and Galactic location.

## Contribution

It presents the first identification of an extreme helium star in 40 years, with detailed spectroscopic analysis and implications for stellar evolution.

## Key findings

- Atmosphere characterized by Teff = 26,170 K and log g = 4.22
- Surface chemistry shows helium with 1% hydrogen and subsolar metallicity
- Consistent with membership in the Galactic bulge

## Abstract

A high-resolution spectrum of the helium-rich `hot subdwarf' GALEX J184559.8-413827 (J1845-4138) obtained with SALT HRS demonstrates it to be the first extreme helium (EHe) star to be discovered in nearly 40 years. A quantitative analysis demonstrates it to have an atmosphere described by Teff = 26 170 +/- 750 K, log g /(cm s^-2) = 4.22 +/- 0.10, and a surface chemistry characterised by CNO-processed helium, a 1% contamination of hydrogen (by number), and a metallicity 0.4 dex subsolar. Its distance and position are consistent with membership of the Galactic bulge. Its sharp absorption lines place strong constraints on both the rotation and microturbulent velocities. Spectroscopically, J1845-4138 closely resembles the pulsating EHe star V652 Her, generally considered to be the product of a double helium white dwarf merger evolving to become a helium-rich sdO star.