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Astron. Astrophys. 326, 165-176 (1997)

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Stellar activity and the Wilson-Bappu relation

Oystein Elgaroy , Oddbjorn Engvold and Per Jorås

Institute of Theoretical Astrophysics, Oslo, Norway

Received 1 April 1996 / Accepted 12 December 1996


The Mg II 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 fulfilled over a range of 18 magnitudes, i.e. from [FORMULA] = +12 to [FORMULA] = -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 [FORMULA] 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.

Key words: stars – chromospheres – coronae – activity

Send offprint requests to: O. Elgaroy

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© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998