1998A&A...337..757E

The rapidly-rotating, chromospherically active late-type star RE 1816+541 has shown signs of intense magnetic activity in various forms. Time-series of high resolution spectra have been obtained during three nights and several important events were detected. Observations contained several chromospheric lines, allowing us investigate simultaneously the response of the chromosphere at different heights. A detailed analysis of the Hα line behaviour, in particular, has revealed prominence clouds and plage-like regions in this star. Rapid rotation favours detection and further investigation of these features. Prominence clouds are seen to lie below the co-rotation radius. A bright plage-like region was well resolved on the first night. The feature disappeared temporarily during meridian crossing, coinciding with the passage of a cloud. Complete obscuration of the plage by the cloud proves that the emission feature is located on or near the stellar surface, whereas the cloud is at larger height and is seen in projection onto it. A very large flare was also detected during the observations, having strong effects in all the chromospheric lines selected for study.