Long-Term Photometric and Chromospheric Variations in V711 Tauri

BAAS, 1996, 28, 942

L.E. DeWarf & E.F. Guinan
Villanova University, Villanova, Pennsylvania
E-Mail: Laurence.DeWarf@Villanova.edu

K. Wong
Lower Merion High School, Ardmore, Pennsylvania

J.D. Dorren
Edinburgh, Scotland

Abstract:

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 V and K1 IV components, and is highly active 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 with the UV emissions, i.e., when V711 Tau is visually bright, the UV emissions are strong, and vice-versa. As first noted by Dorren & 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 supported by NSF Grant AST-9315365 and NASA Grant NAG-2160, which we gratefully acknowledge.

V711 Tauri
Mean Visual Magnitude of V711 Tauri plotted against Julian Date showing the long term changes in brightness most likely arising from an activity cycle. The bars shown in the Figure are the full light amplitude for each seasonal point.