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 Mv values and the Wilson-Bappu relation. Additional Mv values derived from Hipparcos parallaxes are used to explore the systematics. The spectral class dependence vanishes for K-line parameter log W0 ≤ 1.80. Linear spectral class corrections are derived for the more luminous stars, with log W0 ≥ 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 Mv -5 or distance ≈20 kpc.