We have studied the physical parameters of a group of 15 OBA stars from which X-ray emission was detected by the SRG/eROSITA telescope. Whereas the X-ray emission from cool FGKM stars is directly produced near their surface zones—in their chromospheres and coronae—the nature of the X-ray emission from OBA stars requires a separate study in each specific case, since single OBA stars are not intrinsic X-ray sources. We have determined the main physical characteristics of the stars under study, including their effective temperature T₄₅₅ and surface gravity g, based on the spectral energy distribution and the optical spectra obtained with the 1. 5-m Russian–Turkish RTT-150 telescope. An additional analysis of the H line profiles has allowed the possible X-ray emission mechanisms to be assessed: generation in non-stationary stellar winds, collisional processes in circumstellar envelopes, and coronal emission of hidden cool companions. As a result of the analysis, we have concluded that the X-ray emission from eight stars with typical X-ray luminosities in the range Lₗ=28. 5-30. 0 is determined by their hidden late-type companions.
Nikolaeva et al. (Wed,) studied this question.