IUE observations of an active region of HD206860

Abstract

THE chromospheric Mg II h and k lines seem to have doubly reversed emission core in the spectra of the Sun and of solar and late type stars. In the solar spectrum the general appearance of Mg II h and k is very similar to the H and K of Ca II, but with larger intensity fluctuations. Current ideas suggest that the h and k lines are strongly sensitive to chromospheric parameters. In quiet areas of the Sun the Mg II emission shows asymmetric doubly reversed profile with a brighter blue peak, while in plages the emission is much stronger and nearly symmetrical¹. The Mg II doublet seems to be a very useful way of investigating the presence of active regions on stars. We report here the results of our observations of the intensity of the Mg II h and k lines of the star HD206860 collected with the IUE at the Villafranca Satellite Tracking Station of the European Space Agency (ESA). The aim of the observations was to search for short-term variability of the chromospheric emission connected with the rotation period of the star.