B stars seen at high resolution by XMM-Newton

TL;DR

This study analyzes high-resolution X-ray spectra of 11 early B stars, revealing their thermal properties, wind characteristics, elemental abundances, and temporal variability, including pulsations and flares, expanding understanding of B star X-ray emissions.

Contribution

It provides the first high-resolution X-ray analysis of a doubled sample of B stars, detailing their spectral properties, wind mass-loss rates, and variability, with new insights into X-ray pulsations and flaring activity.

Findings

X-ray spectra are typically soft with temperatures of 0.2-0.6 keV.

Half of the stars show temporal variability, including pulsations and flares.

Derived hot wind mass-loss rates sometimes exceed optical predictions.

Abstract

We report on the properties of 11 early B stars observed with gratings on board XMM-Newton and Chandra, thereby doubling the number of B stars analysed at high resolution. The spectra typically appear soft, with temperatures of 0.2--0.6 keV, and moderately bright (log[L_{X}/L_{BOL}]~ -7) with lower values for later type stars. In line with previous studies, we also find an absence of circumstellar absorption, negligible line broadening, no line shift, and formation radii in the range 2 - 7 R*. From the X-ray brightnesses, we derived the hot mass-loss rate for each of our targets and compared these values to predictions or values derived in the optical domain: in some cases, the hot fraction of the wind can be non-negligible. The derived X-ray abundances were compared to values obtained from the optical data, with a fair agreement found between them. Finally, half of the sample presents temporal variations, either in the long-term, short-term, or both. In particular, HD44743 is found to be the second example of an X-ray pulsator, and we detect a flare-like activity in the binary HD79351, which also displays a high-energy tail and one of the brightest X-ray emissions in the sample.