X‐Ray Spectroscopy of the Contact Binary VW Cephei

Abstract

Short-period binaries represent extreme cases in the generation of stellar coronae via a rotational dynamo. Such stars are important for probing the origin and nature of coronae in the regimes of rapid rotation and activity saturation. VW Cep (P=0.28 days) is a relatively bright, partially eclipsing, very active object. Light curves made from Chandra HETGS data show flaring and rotational modulation but no eclipses. Velocity modulation of emission lines indicates that one component dominates the X-ray emission. The emission measure is highly structured, having three peaks. Helium-like triplet lines give electron densities of about (3-18)×1010 cm-3. We conclude that the corona is predominantly on the polar regions of the primary star and is compact.