HETGS Spectroscopy of a Coronally Active Contact Binary, VW Cep

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 d) is relatively bright, partially eclipsing, and very active object. We present preliminary results from Chandra X-ray spectroscopy with the High Energy Transmission Grating. Light curves show flaring and rotational modulation, but no strong eclipses. Emission lines are broader than instrumental, indicating emission from both binary components. Velocity modulation of emission lines is indicative of geometric structure of the emitting plasma. The emission measure shows a broad range of temperatures and strong peak.