The Astrophysical Journal (Jan 2024)
The X-Ray Emission Reveals the Coronal Activities of Semi-detached Binaries
Abstract
X-ray emission is an important tracer of stellar magnetic activity. We carried out a systematic correlation analysis for the X-ray luminosity $\mathrm{log}{L}_{{\rm{X}}}$ , bolometric luminosity $\mathrm{log}{L}_{\mathrm{bol}}$ , and X-ray activity level $\mathrm{log}({L}_{{\rm{X}}}$ / L _bol ) versus the binary parameters including orbital period P , Rossby number R _O , effective temperature T _eff , metallicity [Fe/H], the surface gravity $\mathrm{log}g$ , stellar mass M , and radius R , by assembling a large sample of semi-detached (EB-type) binaries with X-ray emission (EBXs). The fact that both $\mathrm{log}{L}_{{\rm{X}}}$ and $\mathrm{log}{L}_{\mathrm{bol}}$ change in accordance with $\mathrm{log}P$ indicates that X-ray emission originates from the convection zone, while $\mathrm{log}{L}_{{\rm{X}}}$ is proportional to the convection zone area. We found that EBXs with main-sequence components exhibit an upward and then a downward trend in both the $\mathrm{log}{T}_{\mathrm{eff}}$ – $\mathrm{log}{L}_{{\rm{X}}}$ and M – $\mathrm{log}{L}_{{\rm{X}}}$ relations, which is different from the monotonically decreasing trend shown by EBXs containing sub-giant and giant components. The magnetic activity level is negatively correlated with $\mathrm{log}{T}_{\mathrm{eff}}$ and stellar mass. Based on the magnetic dynamo model, the variations in the size and thickness of the surface convection zones can explain the observed relations. EBXs with main-sequence components have a similar R _O – $\mathrm{log}({L}_{{\rm{X}}}/{L}_{\mathrm{bol}})$ relationship to that of the binaries in the clusters as Praesepe and Hyade. We compared the X-ray radiation properties of EBXs with those of the X-ray-emitting contact binaries and found that EBXs have broader value ranges for $\mathrm{log}{L}_{{\rm{X}}}$ and $\mathrm{log}({L}_{{\rm{X}}}$ / L _bol ).
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