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Session 71 - Stellar Activity/Starspots.
Display session, Thursday, June 13
In a continuing effort to more fully understand the highly active RS CVn binary system, V711 Tauri (HR1099, HD22468), ultraviolet and visible light measurements spanning over 15 years are presented. V711 Tau is a short period (Prot = 2.84 days) binary consisting of G5 IV and K1 IV components, and is highly act ive in the short-term, with visual photometric flares of over 0.15 mag and large chromospheric and transition-region flares. Long-term systematic variations in light and in the UV chromospheric and transition- region line emissions have been observed, which may indicate an activity cycle. The Mg II h+k emission lines (280 nm) have been systematically analyzed for over 100 high dispersion IUE archival spectra. C IV (155 nm) and C II (133.5 nm) emission line fluxes have been extracted from all available low
dispersion spectra. This comprehensive data set covers the time interval of 1978 to 1995. Simultaneous multiwavelength photoelectric photometry was obtained at the Villanova University Observatory using the 38 cm reflector and the Automatic Photoelectric Telescopes (APTs) on Mt. Hopkins, Arizona. The IUE data show there is a complex, systematic long-term (> 14 yrs) variation in the stars' chromospheric and transition-region line emissions. The optical light variations appear to be positively correlated w ith the UV emissions, i.e., when V711 Tau is visually bright, the UV emissions are strong, and vice-versa. As first noted by Dorren amp; Guinan (1990, ApJ, 348, 703-711) using a smaller data set, it seems that V711 Tau is similar to our Sun in that the system is optically brightest near the peak of its magnetic activity cycle as inferred from the UV line emissions. This implies that faculae and facular network contribute more to the long-term light variations than do the dark starspots. This research was su pported by NSF Grant AST-9315365 and NASA Grant NAG-2160, which we gratefully acknowledge.
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