Ca II H and K reversals in carbon stars

Nine heavily exposed, high-dispersion blue spectrograms of seven different hot carbon stars were obtained. All spectra show a reversal in the Ca ii H and K lines. The widths of the reversals were measured and, after establishing a calibration, the absolute visual magnitudes of the seven stars were derived. Four of the stars, all ordinary R stars, have absolute magnitudes and colors which place them close to the normal giant branch in the spectral range G8 to K2. The remaining three stars are all hydrogen-deficient carbon stars. All these stars are supergiants, lying along the Ib supergiant branch in a color-magnitude diagram