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

1. Introduction

The systematic broadening of the bright CaII emission lines in spectra of late type stars (surface temperature equal to that of the Sun or cooler) with increasing stellar luminosity (Wilson & Bappu 1957) is of fundamental interest for the understanding of the temperature and density structure of stellar atmospheres. Also the Mg II h and k lines and H Ly show a similar effect (McClintock et al. 1975). Various Wilson-Bappu relations have been established by a number of authors. Engvold & Elgaroy (1987) found that several chromospheric and transition region lines observed with the IUE satellite obeyed W-B relationships. A study of the relation between stellar activity and the W-B relation using a sample of 78 single stars has recently been carried out by Elgaroy et al. (1997). A numerical simulation of the Wilson-Bappu relationship has recently been carried out by (Cheng et al. 1997).

A problem encountered in previous investigations is uncertainties in the absolute magnitude of the sample stars, since this parameter enters directly in the Wilson-Bappu relation. The uncertainties were not likely to severely affect the general trend of the relationship in a comprehensive sample of stars, but investigations of fine structure in the diagrams such as deviations from the regression line met with difficulties. The problem was that the errors in absolute magnitudes of the stars, in particular the more distant ones were unknown. Uncertainties in the line widths were more easy to handle since these could be estimated during the processing of the data.

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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