Emission lines in the wings of CA II H and K. II - Stellar observations: Dependence of line width on luminosity and related topics

Weak emission lines in the extensive wings of the Ca II H and K resonance lines are studied using high-dispersion spectrograms of 48 bright MK standard stars of all luminosity classes and spectral types F, G, K, and M. It is found that weak absorption lines in spectra of dwarf stars become weak emission lines as luminosity increases for a given spectral type and that this variation resembles the center-to-limb variation of similar lines in the solar spectrum. Evidence is obtained indicating that the transition from absorption to emission begins in early F supergiants, continues through G-type bright giants, and ends with the K and M giants. It is shown that the line-depth or contrast variation of H-K wing emission with luminosity in a given spectral type mimics the center-to-limb variation of line-depth or contrast of solar H-K wing emission and that there is a correlation between line width and luminosity for H-K wing emission that is analogous to the Wilson-Bappu effect in H-K core emission. The apparent sensitivity of this correlation to the depth of line formation is used to investigate the depth dependence of total nonthermal broadening velocity and differential motions in several stars of different spectral types and luminosity classes.