The effect of extremely rapid rotation on stellar activity: The case of gliese 890

Abstract

We present an analysis of broad-band photometry and of the H-alpha emission line profile of the active, rapidly rotating (P = 0.43 days) single M-dwarf star Gleise 890. Our analysis suggests that the (presumed dark) spots and the bright emission regions are confined to high latitudes on the star. We combine our results with published work on other rapidly rotating single stars which indicate that such activity is generally confined to the polar regions of such stars, and we contrast that to rapidly rotating active components in binary systems where the active regions do not appear to be confined to the polar latitudes. Noting that solar activity is confined to lower latitudes and seems unable to affect polar latitudes, we suggest that extremely rapid rotation may ater the convective turnover time in the equatorial latitudes, and that strong tidal coupling may restore it to normal values in spite of rapid rotation. The evidence suggests that even though radiative power losses due to activity may be comparable in single and binary stars, the driving mechanisms may differ appreciably.