Near-simultaneous X-ray and optical observations of the RS Canum Venaticorum binary SV Camelopardalis

Wereport on amulti-wavelength campaign of optical and X-ray observations of the short-period eclipsing RS CVn binary star SV Cam. We present an X-ray light curve measured by ROSAT in Aug. 93, two V -band light curves obtained in Sep. and Nov. 93, and Doppler imagery based on high-resolution spectroscopy of photospheric absorption lines observed Sep.–Nov. 93. The total X-ray output of the SV Cam binary was found to be on a level typical for single main sequence stars. Thus SV Cam does not appear to be overactive, contrary to what is generally claimed for RS CVn systems. We model theX-ray light curvewith two extended coronal emission regions. One region is located above a photospheric region of the primary star where spots have frequently been observed and where we find evidence for photospheric spots from our optical data. The second X-ray source in our model is located between the two components of the binary. Our Doppler image shows a distinct spot on the primary star centred at a stellar latitude of 60◦. This spot is also found in an analysis of the optical light curve observed in September. A second spot in the Doppler image, which appears as an appendage to the main feature, seems to be spatially correlated with the second X-ray source. While our analysis yields no evidence for this feature in the September light curve it clearly determines the November light curve indicating rapid evolution of an active spotted region. Furthermore, we find evidence of strong (chromospheric) activity on the secondary star of SV Cam. During secondary eclipse the strength of the Hα absorption line of the single-lined binary increases by a much larger factor than can be accounted for by continuum light (or lack thereof) from the secondary indicating strong Hα emission from the secondary star. Also during primary eclipse absorption features from the secondary star become visible in all photospheric lines except Hαwhich argues strongly for the lack of Hα absorption and, hence, for the appearance of significant amounts of Hα emission in the secondary star. Send offprint requests to: Alexander Hempelmann (e-mail: [email protected])