Hot stars observed by XMM-Newton
Groupe d’Astrophysique des Hautes Energies, STAR, Université de Liège, Quartier Agora (B5c, Institut d’Astrophysique et de Géophysique), Allée du 6 Août 19c, 4000 Sart Tilman, Liège, Belgium
2 Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, 11 rue de l’Université, 67000 Strasbourg, France
Accepted: 30 August 2018
We perform a survey of Oe and Be stars in the X-ray range. To this aim, we cross-correlated XMM-Newton and Chandra catalogs of X-ray sources with a list of Be stars, finding 84 matches in total. Of these, 51 objects had enough counts for a spectral analysis. This paper provides the derived X-ray properties (X-ray luminosities, and whenever possible, hardness ratios, plasma temperatures, and variability assessment) of this largest ever sample of Oe and Be stars. The targets display a wide range in luminosity and hardness. In particular, the significant presence of very bright and hard sources is atypical for X-ray surveys of OB stars. Several types of sources are identified. A subset of stars display the typical characteristics of O-stars, magnetic OB stars, or pre-main-sequence (PMS) objects: their Be nature does not seem to play an important role. However, another subset comprises γ Cas analogs, which are responsible for the luminous and hard detections. Our sample contains seven known γ Cas analogs, but we also identify eight new γ Cas analogs and one γ Cas candidate. This nearly doubles the sample of such stars.
Key words: stars: early-type / stars: emission-line Be / X-rays: stars / stars: individual: γ Cas
Based on observations collected with NASA missions Chandra and Swift as well as the ESA observatory XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).
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© ESO 2018