A large spectral class dependence of the Wilson-Bappu effect among luminous stars

The striking correlation between Ca II K-line emission width and absolute visual magnitude has not previously been well calibrated for stars more luminous than giants. From a sample of binary systems fit to isochrones, we find deviations of more than 2 mag, correlated with spectral class, between these binarity M-nu values and the Wilson-Bappu relation. Additional M-nu values derived from Hipparcos parallaxes are used to explore the systematics. The spectral class dependence vanishes for K-line parameter log W-0 less than or equal to 1.80. Linear spectral class corrections are derived for more luminous stars, with log W-0 greater than or equal to 2.00, while a table is provided for the transition region. The dispersion from these relations is about+/- 0.6 mag. This recalibration extends the demonstrated applicability of the Wilson-Bappu technique to M-nu similar or equal to -5 or distance approximate to 20 kpc.