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Paper: X-ray and Optical Properties of New γ Cas-Like Objects Discovered in X-ray Surveys
Volume: 361, Active OB-Stars: Laboratories For Stellar and Circumstellar Physics
Page: 117
Authors: Motch, C.; Lopes de Oliveira, R.; Negueruela, I.; Haberl, F.; Janot-Pacheco, E.
Abstract: A growing number of early Be stars discovered in X-ray surveys exhibit X-ray luminosities intermediate between those of normal stars and those of most Be/X-ray binaries in quiescence. Their X-ray spectra are also much harder than those of shocked wind OB stars and can be best fitted by a thin thermal plasma with T ∼ 108 K, added to a cooler and much fainter thermal component. An iron line complex including a fluorescence component is detected in many cases. There is no evidence for coherent pulsations in any of these systems but strong variability on time scales as short as 100 s is usually observed. Large oscillations with quasi-periods of the order of one hour or more are detected in the X-ray light curves of several sources, but have so far failed to prove to be strictly periodic. The optical and X-ray properties of these new objects strikingly resemble those of the so far unique and enigmatic Be star γ Cas and define a new class of X-ray emitters. We discuss the possible origin of the X-ray emission in the light of the models proposed for γ Cas, magnetic disc-star interaction or accretion onto a compact companion object – neutron star or white dwarf.
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