A growing number of early Be stars exhibit X-ray luminosities intermediate between those typical of early type stars and those emitted by most Be/X-ray binaries in quiescence .
We report on XMM- Newton observations of two such Be stars , SAO 49725 and HD 161103 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 excess ( L _ { X } \sim 10 ^ { 32 - 33 } erg s ^ { -1 } ) and the hardness of their X-ray spectra which are both unusual for normal early type stars .
An iron K \alpha complex is clearly detected in HD 161103 in which the H-like , He-like and fluorescent components are resolved , while strong evidences also exist for the presence of similar features in SAO 49725 .
X-ray spectra can be equally well fitted by a thermal plasma ( mekal ) with T \sim 10 ^ { 8 } K and solar abundances or by a power law + iron line model with photon index \sim 1.5–1.8 , both with a soft thermal component with T \sim 10 ^ { 7 } K. The intensity of the fluorescence 6.4 keV line reflects the presence of large amounts of cold material close to the X-ray sources and strongly argues against accretion onto a companion neutron star in a large orbit .
On the other hand , the probable thermal origin of the X-ray emission as supported by the ionised iron lines is in disagreement with those observed in all known Be/X-ray binaries , in which a non-thermal component is always required .
Remarkably , the X-ray features are similar to those of white dwarves in several cataclysmic variables .
There is no evidence for high frequency pulsations in none of the two systems .
However , a large oscillation in the light curve of HD 161103 with P \sim 3200 s is readily detected .
The X-ray light curve of SAO 49725 exhibits clear variability by \sim 80 % on time scales as short as \sim 1000 s. New optical observations provide updated spectral types ( B0.5 III-Ve ) , and disclose a dense , large and apparently stable circumstellar disc for both stars .
The nature of the excess X-ray emission is discussed 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 .
These two new objects added to similar cases discovered in XMM- Newton surveys point at the emergence of a new class of $ γ $ Cas analogs .