  We have obtained a densely sampled time series of CaII H&K line profiles of
the ultrafast rotating K-dwarf star BO Mic. Taken at high resolution, the
spectra reveal pronounced variations of the emission core profiles. We
interpret these variations as signs of concentrated chromospherically active
regions, in analogy to solar plages. We further interpret the variations as
partly due to the rapid growth and decay of plages, while other variations
appear to be caused by plages moved over the visible stellar disk by rotation.
The equivalent width of the Ca K core emission changes approximately in
anti-phase to the photospheric brightness, suggesting an association of the
chromospheric plage regions with pronounced dark photospheric spots. We believe
that further analysis of the presented spectral time series will lead to a
chromospheric Doppler image of BO mic.
