Extensions of the Wilson-Bappu effect among very luminous stars

It has been stated that the technique used by Wilson and Bappu (1957) in their study of the observational correlation of M sub V and the logarithm of the full width at half maximum of the Ca II K-line central emission for G, K, and M stars has a plus or minus 0.5 mag accuracy. A tabulation by Wilson (1976) suggests, however, that the error may be only plus or minus 0.3 mag. This accuracy makes the approach valuable for late-type supergiants since other methods suffer from comparable errors. A description is in this connection presented of a new class of emission lines in late-type giant and supergiant spectra that exhibit M sub V correlated widths, yet are detectable among the brightest stars.