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Astron. Astrophys. 343, 222-228 (1999)

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The Wilson-Bappu effect of the MgII k line - dependence on stellar temperature, activity and metallicity

Oystein Elgaroy 1, Oddbjorn Engvold 1 and Niels Lund 2

1 Institute of Theoretical Astrophysics, Oslo, Norway (e-mail: oddbjorn.engvold@astro.uio.no)
2 Danish Space Research Institute, Copenhagen, Denmark (e-mail: nl@dsri.dk)

Received 1 October 1997 / Accepted 10 March 1998

Abstract

The Wilson-Bappu effect is investigated using accurate absolute magnitudes of 65 stars obtained through early release of data from the Hipparcos satellite together with MgII k line widths determined from high resolution spectra observed with the International Ultraviolet Explorer (IUE) observatory.

Stars of spectral classes F, G, K and M and luminosity classes I-V are represented in the sample. Wilson-Bappu relations for the Mg II k line for stars of different temperatures i.e. spectral classes are determined. The relation varies with spectral class and there is a significant scatter of the line widths around the regression lines.

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. A difference in behavior between dwarfs and giants (and supergiants) of spectral class K seems to be present. Magnetic activity affects the width of the Mg II k line in dwarfs. Metallicity is found to influence the Mg II k line width in giants and supergiants. Possible interpretations of the new results are briefly discussed.

Key words: stars: activity – stars: chromospheres

Send offprint requests to: O. Engvold (e-mail: oddbjorn.engvold@astro.uio.no)

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© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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