HD45314: a new gamma Cas analog among Oe stars

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.

Accepted for publication as a Letter in Astronomy & Astrophysics

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• Three discoveries of gamma Cas analogs from dedicated XMM-Newton observations of Be stars
• pi Aqr is another gamma-Cas object
• Intriguing X-ray and optical variations of the gamma Cas analog HD45314
• High-Energy Properties of the Enigmatic Be Star gamma Cassiopeiae
• The VLT-FLAMES Tarantula survey XX. The nature of the X-ray bright emission line star VFTS 399
• A Time-Dependent Spectral Analysis of $\gamma$ Cassiopeiae
• Spectroscopic variability of two Oe stars
• Irregular emission cycles in the Oe star HD 60848