Photometry of Cool Stars Detected in EUV All-Sky Surveys

G. Cutispoto, G. Tagliaferri, M. Kürster, M. Rodonò

Presentations at the 10th Cambridge Workshop ``Cool Stars, Stellar Systems and the Sun,'' Cambridge, MA, 1997 July 15-19

Abstract

Observations at X-Ray and EUV wavelengths have proven to be an excellent way to discover previously unrecognized active stars. In fact, flux-limited X-ray and EUV surveys are strongly biased towards objects with intrinsically high levels of chromospheric and coronal emission. The inspection of the cool star content of X-ray and EUV surveys shows that they contain, in addition to already catalogued RS CVn and BY Dra-type binaries and dMe flare stars, a significant number of stars for which very little or no information is available. These objects are primary targets for follow-up optical photometry and spectroscopy in an attempt to determine their physical nature. As a contribution in this direction, we present U BV (RI)c photometry of stellar sources detected in the EUV by the ROSAT and EUVE satellites during their all-sky surveys. For all the stars we infer approximate spectral classification and distance and derive photometric periods for the variable ones. Although limited in number, these results show the rich amount of information on active stars contained in EUV surveys.

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