EUVE Observations of AR Lac During Eclipse

AR Lac is a double-lined spectroscopic binary of the RS CVn class. The binary system is composed of G2IV and K0IV members with an orbital period of 1\.98 days. Because of the system's 87(deg) inclination, the G star is totally eclipsed by the K star once every two days. During the calibration phase of the Extreme Ultraviolet Explorer (EUVE) mission, we observed AR Lac during eclipse and at the following quadrature. The observation of the eclipse allowed determination of the relative EUV fluxes from the individual members. Assuming that there are no localized regions of intense EUV emission, we determine that about one-third of the system's emission comes from the K star. Evidence for long-term variability in the system is also seen as the mean EUV count rates are lower during observations from the all-sky survey four months later. This work has been supported by NASA contracts NAS5-30180 and NAS5-29298.