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J.J. Drake (1), A. Brown (2,3), R.J. Patterer (1), P. Vedder (1), S. Bowyer (4), and E.F. Guinan (5)
1) Center for EUV Astrophysics, University of California, 2150
Kittredge Street, Berkeley, CA 94720
2) Joint Institute for Laboratory Astrophysics, University of
Colorado, Boulder, CO 80309
3) National Institute of Standards and Technology, Boulder, CO
80309
4) Astronomy Dept., University of California, Berkely, Ca. 94720
5) Dept. of Astronomy and Astrophysics, Villanova University,
Villanova, PA 19085
The RS CVn binary V711 Tauri was observed by the Extreme Ultraviolet Explorer satellite (EUVE) twice during the latter half of 1992, for periods lasting several days. Light curves for the waveband 60-180 Å derived from the all-sky survey scanning in August, and from a pointed calibration observation made in October, both exhibit a modulation of about 40%. The modulation in both data sets is very similar, with minimum flux occurring near orbital phase phi = 0.5. Analysis using a two temperature optically thin plasma emission model reveals that most of the detected extreme ultraviolet (EUV) flux emanates from hot (~1E+07 K) coronal plasma. The modulation is pro- bably mostly due to either flare-like activity or to rotational occultation of a long-lived, compact and especially bright coronal structure on the more active star of the system. The phased data support the latter hypothesis. This coronal structure is then likely to be associated with the persistent spot patterns seen on V711 Tau when using Doppler and photometric surface imaging techniques. Comparison with contemporaneous Stromgren b-band photometry indicates that the optical minimum light leads the EUV maximum light by 90 degrees in phase.
Subject Headings: stars: activity -- coronae -- late-type -- binaries: close -- X-rays: stars
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