Near-simultaneous X-ray and optical observations of the RS CVn binary SV Cam

We report on a multi-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 the X-ray light curve with 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 H#alpha# 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 H#alpha# emission from the secondary star. Also during primary eclipse absorption features from the secondary star become visible in all photospheric lines except H#alpha# which argues strongly for the lack of H#alpha# absorption and, hence, for the appearance of significant amounts of H#alpha# emission in the secondary star. (orig.)SIGLEAvailable from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman