Hard X-rays from the contact binary VW Cephei

Ginga observations of the contact binary VW Cep are presented. The observed X-ray luminosity is 1.1×10 30 erg/s in the energy range of 2-10 keV, assuming a distance of 31 pc. No evidence for X-ray orbital modulation or for flare events was seen. The observed X-ray spectrum is very hard, and can be represented well either by a thermal bremsstrahlung model with a temperature of 11.2 keV or a power-law model with photon index of Γ = 1.90. These observational results are interpreted in terms of thermal emission from hot coronal plasma extending beyond the stellar size. However the observed upper limit on the iron K-line intensity is considerably below the theoretical prediction