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Abstract <p>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 <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(T_{\textrm{eff}}\)</EquationSource> <!--Letters2670002Nikolaeva-m1--> </InlineEquation> and surface gravity <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\log g\)</EquationSource> <!--Letters2670002Nikolaeva-m2--> </InlineEquation>, 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<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\({\alpha}\)</EquationSource> <!--Letters2670002Nikolaeva-m3--> </InlineEquation> 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 <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\log L_{\textrm{X}}=28.5{-}30.0\)</EquationSource> <!--Letters2670002Nikolaeva-m4--> </InlineEquation> is determined by their hidden late-type companions.</p>

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Study of Massive OBA Stars with X-ray Emission

  • 期刊论文

  • 发表日期：

    2025年10月1日

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  • E. A. Nikolaeva,
  • I. F. Bikmaev,
  • E. N. Irtuganov,
  • M. R. Gilfanov,
  • R. A. Sunyaev,
  • P. S. Medvedev

摘要

Abstract

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 \(T_{\textrm{eff}}\) and surface gravity \(\log g\) , 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 \({\alpha}\) 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 \(\log L_{\textrm{X}}=28.5{-}30.0\) is determined by their hidden late-type companions.