Comparing the Ca II H and K emission lines in red giant stars.
RYON J., SHETRONE M.D. and SMITH G.H.
Abstract (from CDS):
Measurements of the asymmetry of the emission peaks in the core of the Ca II H line for 105 giant stars are reported. The asymmetry is quantified with the parameter VIR, defined as the ratio between the maximum number of counts in the blueward peak and the redward peak of the emission profile. The Ca II H and K emission lines probe the differential motion of certain chromospheric layers in the stellar atmosphere. Data on VIR for the Ca II K line are drawn from previous papers and compared to the analogous H-line ratio, the H and K spectra being from the same sets of observations. It is found that the H-line (VIR) value is +0.04 larger, on average, than the equivalent K-line ratio, however, the difference varies with B-V color. Red giants cooler than B-V = 1.2 are more likely to have (VIR)H > (VIR)K, whereas the opposite is true for giants hotter than B-V = 1.2. The differences between the Ca II H and K-line asymmetries could be caused by the layers of chromospheric material from which these emission features arise moving with different velocities in an expanding outflow.