X-rays from Hot Subdwarfs

TL;DR

This paper reviews recent X-ray observations of hot subdwarfs, highlighting their emission mechanisms, binary systems, and implications for stellar wind studies, made possible by advanced space telescopes like XMM-Newton and Chandra.

Contribution

It summarizes the current understanding of X-ray emission from hot subdwarfs, emphasizing new insights from recent high-sensitivity observations and their relevance to stellar wind physics.

Findings

X-ray emissions originate from wind accretion in binary systems.

Isolated sdO stars show X-rays likely due to wind shock instabilities.

X-ray studies help understand winds of massive early-type stars.

Abstract

Thanks to the high sensitivity of the instruments on board the XMM-Newton and Chandra satellites, it has become possible to explore the properties of the X-ray emission from hot subdwarfs. The small but growing sample of hot subdwarfs detected in X-rays includes binary systems, in which the X-rays result from wind accretion onto a compact companion (white dwarf or neutron star), as well as isolated sdO stars in which X-rays are probably due to shock instabilities in the wind. X-ray observations of these low mass stars provide information which can be useful also for our understanding of the winds of more luminous and massive early-type stars and can lead to the discovery of particularly interesting binary systems.