A hard and variable X-ray emission from the massive emission line star HD 157832

TL;DR

This paper reports the discovery of variable, high-temperature X-ray emission from the Be star HD 157832, a unique gamma-Cas-like system with a dense circumstellar disc, providing insights into the origin of high-temperature X-ray emission in such stars.

Contribution

It identifies HD 157832 as the coolest gamma-Cas analog with high X-ray variability, expanding understanding of X-ray emission mechanisms in Be/X-ray systems.

Findings

HD 157832 exhibits hard-thermal X-ray emission at ~130 MK.

The star's soft X-ray luminosity varies by over a factor of 3 in 14 years.

HD 157832 is the coolest known gamma-Cas analog.

Abstract

We report the discovery of a hard-thermal (T ~ 130 MK) and variable X-ray emission from the Be star HD 157832, a new member of the puzzling class of gamma-Cas-like Be/X-ray systems. Recent optical spectroscopy reveals the presence of a large/dense circumstellar disc seen at intermediate/high inclination. With a B1.5V spectral type, HD 157832 is the coolest gamma-Cas analog known. In addition, its non detection in the ROSAT all-sky survey shows that its average soft X-ray luminosity varied by a factor larger than ~ 3 over a time interval of 14 yr. These two remarkable features, ``low'' effective temperature and likely high X-ray variability turn HD 157832 into a promising object for understanding the origin of the unusually high temperature X-ray emission in these systems.