Discovery of optical circular polarization in Lambda Andromedae

Abstract

It is found that the RS CVn-type star has variable broad-band optical circular polarization, of amplitude 0.002-0.004 percent, based on 59 nights' data during 1982, 1985, and 1986. The variability is compared with contemporaneous light curves. Ordered magnetic fields of possibly about 1 kG, in large spots, appear to be present at times. The polarization and light curves were markedly different in different years, owing to evolution of the spot geometry. The patterns switched from predominant variation on the 54 day rotation period to double-peaked curves (period 27 days), but a curious anticorrelation is seen between the variation time scale of the light and polarization. A qualitative model is offered for one case.