NEAR-SIMULTANEOUS X-RAY AND OPTICAL OBSERVATIONS OF THE RS CANUM-VENATICORUM BINARY SV CAMELOPARDALIS

We report on a multi-wavelength campaign of optical and X-ray observat ions of the short-period eclipsing RS CVn binary star SV Cam. We prese nt 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 hig h-resolution spectroscopy of photospheric absorption lines observed Se p.-Nov. 93. The total X-ray output of the SV Cam binary was found to b e 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 the X-ray light curve with two extended coro nal emission regions. One region is located above a photospheric regio n of the primary star where spots have frequently been observed and wh ere we find evidence for photospheric spots from our optical data. The second X-ray source in our model is located between the two component s of the binary. Our Doppler image shows a distinct spot on the primar y star centred at a stellar latitude of 60 degrees. 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-r ay source. While our analysis yields no evidence for this feature in t he September light curve it clearly determines the November light curv e 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 H alpha a bsorption line of the single-lined binary increases by a much larger f actor than can be accounted for by continuum light (or lack thereof) f rom the secondary indicating strong H alpha emission from the secondar y star. Also during primary eclipse absorption features from the secon dary star become visible in all photospheric lines except H alpha whic h argues strongly for the lack of H alpha absorption and, hence, for t he appearance of significant amounts of H alpha emission in the second ary star.