High-latitude spot and plage activity on the rapidly rotating M dwarf star Gliese 890

Simultaneous time-resolved observations in broadband photometry and in H-alpha and near-UV spectroscopy are presented of Gliese 890, a single M dwarf of the BY Draconis type with the shortest known period of rotation among field stars of its type. The continuum light curves exhibit modulations characteristic of the presence of localized dark spot regions, and the spectra show corresponding modulations of the intensity of H-alpha emission, with the latter being substantially in phase with the former. Secular changes in the continuum light curve indicate that the geometry of the spots changes appreciably over time scales of the order of 60 rotation periods. The overall chromospheric activity is not significantly greater than that found in similar stars which rotate much more slowly. The principal active region present on the visible disk of the star during the observations appear to be at a remarkably high latitude compared to the occurrence of such regions on the sun. 25 refs.