An Observational and Theoretical Investigation of Calcium II Hydrogen and Potassium Emission in Yellow Supergiants and Classical Cepheids.

Relative flux profiles for the Ca II H and K lines in yellow supergiants and classical Cepheid variables were obtained from spectrographic observations made at Kitt Peak National Observatory and the Blue Mesa station of the N.M.S.U. Observatory. The data confirm that the Ca II emission width in Cepheids violates the Wilson-Bappu (W-B) relationship for nonvariable stars. However, the profiles for zeta Gem reveal previously unreported Ca II emission on the falling branch of the light curve just past maximum light. Since this emission is not as wide as that which normally occurs on the rising branch, an internal contradiction to the W-B relation is suggested. The discrepancy between the emission widths in Cepheids and yellow supergiants is examined.