XMM-Newton observations of low luminosity Be/X-ray candidates

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XMM-Newton observations of low luminosity Be/X-ray candidates

Lopes de Oliveira, R. / Motch, C. / Haberl, F. / Negueruela, I. / Janot-Pacheco, E.

AbstractA small number of early Be stars exhibit X-ray luminosities intermediate between those typical of early type stars and those radiated by Be/X-ray binaries in the quiescent state. We report on XMM-Newton observations of two such Be stars, HD 161103 and SAO 49725 which were originally discovered in a systematic cross-correlation between the ROSAT all-sky survey and SIMBAD. The new observations confirm the X-ray luminosity detected by ROSAT (LX∼10³²ergs⁻¹) and the hardness of their X-ray spectra (thin thermal with kT∼8–10keV or power law with photon index of ∼1.7) which are both unusual for normal early type stars. We discuss the possible origin of this excess 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, and compare the properties of these two sources with those of the new massive systems discovered in the XMM- Newton/SSC survey of the Galactic plane.