Stellar activity and the Wilson-Bappu relation

The MgII h and k lines of 78 single stars observed with the International Ultraviolet Explorer (IUE) observatory have been analyzed. Stars of spectral classes F, G, K and M and luminosity classes I-V are represented in the sample. From these data it is shown that the Wilson-Bappu relation for the Mg II h and k lines is furfilled over a range of is magnitudes, i.e. from M-v = +12 to M-v = -6. The sample contains slowly rotating stars of different activity levels and is suitable for investigations of a possible relation between line width and stellar activity. It is found that active stars have broader lines and show a larger variation in line widths than quiet stars. Observations of the active RS CVn binary sigma Gem taken at epochs when it shows different levels of activity, clearly demonstrate line broadening following higher activity. Possible implications of the new results for the interpretation of the Wilson-Bappu relation are briefly discussed.