The V -Stokes Parameter as a Manifestation of Envelope Activity for Cool, Bright, Evolved Stars

At Pennsylvania’s Flower and Cook Observatory, instrumentation has been developed to measure simultaneously the four Stokes parameters of the filtered radiation field from a celestial source. The instrumental Q / U / V -parameters have been found to be very small and well-behaved. Thus far, the program has concentrated on cool bright giants and supergiants and on hot, evolving close binaries. A single season’s investigation of Alp Ori has already been reported (Holenstein 1987) and the present paper is a summary of current results for the cool, evolved program stars. For Psi 1 Aur, V CVn, 6 Gem, 72 Leo and 119 Tau no V -signal at the level of 3 σ has been detected from data from the 1986-1987 season. At the level of 0.0n%, unambiguous and variable V -signals have been detected for VV Cep, Mu Cep, Alp Her, Alp Ori, Bet Peg, and Alp Sco.