The relationship between soft X-rays and the 1640 A feature fluxes inlate-type stars.

Abstract

The relationship between the soft X-ray flux and the wavelength 1640 feature in a sample of late-type stars is studied. It is assumed that all the observed feature intensity comes from the helium line and that only the fraction of the He II line due to recombination is directly related to the X-ray flux. A close correlation is found between both fluxes for solar-type stars. This relation is independent of the luminosity class, and is valid for stars with rather different coronal temperatures. Fe II contribution to the wavelength 1640 blend could be negligible, except in the nonsolar type stars, where this ion can be the main contributor to the line intensity. The empirical relationship obtained in this paper is also used to derive the X-ray flux for some stars that have not been observed in the X-ray range.