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 logLX , bolometric luminosity logLbol , and X-ray activity level log(LX /L bol) versus the binary parameters including orbital period P, Rossby number R O, effective temperature T eff, metallicity [Fe/H], the surface gravity logg , 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 logLX and logLbol change in accordance with logP indicates that X-ray emission originates from the convection zone, while logLX 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 logTeff – logLX and M– logLX 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 logTeff 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(LX/Lbol) 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 logLX and log(LX /L bol).