A Long-Term Study of Hα Line Variations in FK Comae Berenices

We present observations of Hα V/R ratio variations in FK Comae Berenices obtained during several observing seasons from 1981 to 1992. The raw Ha emission profile is always observed to be double peaked due to the stellar-absorption component. During most years the V/R ratio varies regularly with the period of the photometric light curve. The V/R periodicity is most obvious when time spans no longer than several stellar rotations are considered. We propose that the bulk of the emission component of the Hα line arises in corotating circumstellar material that may be similar to that of a quiescent solar prominence. The lifetime of these structures appears to be on the order of weeks. A weak contribution from a circumstellar disk is evident and chromospheric emission may also be present. The appearance or disappearance of circumstellar structures over periods longer than a few weeks, or the total absence of such structures, blurs the more regular variations in Ha seen over short time scales. Other more stochastic activity, such as flares, also clearly occurs. Phase shifts of the V/R ratio from year to year rule out the hypothesis that mass transfer in a close binary system is responsible for the V/R variations.