Regular variations in the H-alpha profile of FK Comae

A series of observations of the rapidly rotating G type giant FK Comae are presented. The unusually broad H-alpha profile is seen to vary regularly in the sense that the violet-to-red emission ratio is correlated with photometric phase and presumably with rotation. These observations are described by an excretion disk model with substantial density inhomogeneities driven at the angular velocity of the star by an imbedded magnetic field. That sufficient magnetic flux is available is suggested by both the high observed v sin i of about 120 km/s and photometric evidence of starspots.