WIDTHS OF CA II CHROMOSPHERIC EMISSION LINES AS A MEASURE OF STELLAR LUMINOSITY

Abstract

I. The Original Calibrations Emission components in the centers of the H and Κ Ca π absorption lines of several late-type stars were found by Eberhard and Schwarzschild in 1913, although they had already been known in the solar spectrum for many years. These lines were observed in additional stars in 1922 by Deslandres and Burson, and Stratton (1925) noted that these observations showed the line widths to increase with luminosity. The latter two of the foregoing references were unknown to the writer until quite recently. Wilson showed (1954) that the H-K emission widths correlated with the absolute magnitudes of the stars. The Mount Wilson spectroscopic absolute magnitudes were used for this purpose, and the resulting relationship was nonlinear. A more extensive investigation, including many more stars, was then made by Wilson and Bappu (1957). These observers obtained 10 Â mm'1 spectrograms of most of the appropriate standard stars of the MK system, thus using absolute magnitudes much improved over the old Mount Wilson values; and also, after subtracting a fixed slit width correction, they plotted the logarithm of the corrected line widths against the MK absolute visual magnitudes. A straight line extending over more than twelve magnitudes was drawn by eye through the plotted points. Sorting the stars by spectral type and by emission strength indicated no dependence of the width-luminosity relationship upon either of these quantities.