The Ca II-Mv correlation (Wilson-Bappu effect) calibrated by Hipparcos parallaxes

We have used Hipparcos parallaxes to derive absolute visual magnitudes of G, K, and M stars with Ca II emission line widths previously measured by O. C. Wilson. A linear relationship similar to the one derived originally by Wilson & Bappu and improved by Lutz & Kelker was found from M-v = + 7 to -2. For stars brighter than M-v = -2 a substantial number of stars show Ca II emission lines that are broader than expected from the linear fit. Most of those stars are bright giants and supergiants of type G. In appendices we show some sample Ca II profiles and identify emission lines of Fe II as well as the H epsilon line in some stars.