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

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

Abstract

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 = +12 to = -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 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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Contents

• 1. Introduction
• 2. The data
• 3. Data processing and analysis of the profiles
• 4. Results
  • 4.1. The Wilson-Bappu relation for Mg II
  • 4.2. Stellar activity parameters
    • 4.2.1. The Mg II surface flux: a direct activity measure
    • 4.2.2. The Mg II h/k ratio: as a measure of activity
  • 4.3. The Wilson-Bappu relations for quiet and active stars
• 5. Discussion and concluding remarks
• References

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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