The X-Ray Emission Reveals the Coronal Activities of Semi-detached Binaries

Abstract

Abstract X-ray emission is an important tracer of stellar magnetic activity. We carried out a systematic correlation analysis for the X-ray luminosity log L X , bolometric luminosity log L bol , and X-ray activity level log ( L 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 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 log L X and log L bol change in accordance with log P indicates that X-ray emission originates from the convection zone, while log L 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 log T eff – log L X and M– log L 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 log T 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– log ( L X / L 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 log L X and log ( L X /L bol).