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Session 67 - Stars: Evolution, Atmospheres, Intrinsic.
Display session, Thursday, June 11
Atlas Ballroom,
The H\alpha activity in the eclipsing binary system V471 Tauri was measured as a function of phase over three Epochs at both KPNO and Lick Observatory. Epoch 1 observations, taken in 1987 at Kitt Peak, showed dramatic variation in the strength of the H\alpha line (from complete absorption when the K-dwarf eclipsed the W.D. companion to strong emission when the W.D. transited the cooler K-dwarf star). Epoch 2 observations, taken in 1990 also at Kitt Peak, showed less variation in the strength of H\alpha line, although it still exhibited weak emission on the side of the K2 star facing the white dwarf. Epoch 3 observations, taken in 1992 at Lick observatory, showed no emission at all phases although there was some filling of the H\alpha absorption spectrum measured close to and during the transit (phase 0.5) of the K2 by the white dwarf. The implication of these measurements is that reprocessing of UV radiation from the W.D. in the chromosphere of the K2 companion is negligible and cannot be used to interpret the high levels of H\alpha activity observed in Epoch 1. A further implication is that chromospherically active regions on the K-dwarf form preferentially around the sub-stellar point of the white dwarf. We discuss the possibility that tidal coupling affects the longitude of active region formation.
