HD45314: a new gamma Cas analog among Oe stars

TL;DR

This paper reports the discovery of HD45314 as a gamma Cas analog among Oe stars, based on its unique hard X-ray emission and variability, suggesting the presence of a star-disk interaction.

Contribution

The study identifies HD45314 as the first gamma Cas analog among Oe stars, providing new insights into their X-ray properties and potential disk interactions.

Findings

HD45314 exhibits very hard X-ray emission with kT ~ 21 keV.

HD45314 shows count rate variations by a factor of 2 within ~1000 seconds.

HD45314 has a high log(L_X/L_bol) ratio of -6.10, indicating strong X-ray activity.

Abstract

Oe stars possibly form an extension to higher temperatures of the Be phenomenon, but it is still unclear whether these stars have disks. X-ray spectra could provide hints for interactions of the star with a putative surrounding disk. We obtained XMM-Newton observations of two Oe stars, HD45314 and HD60848. Spectra and light curves were extracted and analysed. Optical spectra were also obtained to support the X-ray observations. We find that both stars display very different X-ray properties. Whilst HD60848 has an X-ray spectrum and emission level typical for its spectral type, HD45314 displays a very hard X-ray emission, dominated by a thermal plasma with kT ~ 21 keV. Furthermore, HD45314 displays count rate variations by a factor 2 on timescales of ~ 1000s and a high log(L_X/L_bol) = -6.10 +/- 0.03. The X-ray properties of HD45314 indicate that this star is a new member of the class of gamma Cas analogs, the first one among the original category of Oe stars.