Stellar model chromospheres. XI - A survey of CA II lambda 8542 line profiles in late-type stars of differing chromospheric activity

Abstract

We have obtained profiles of the Ca II infrared triplet line λ8542 in 49 stars of spectral type F9-K3. These data were obtained with a silicon diode vidicon detector system on the KPNO McMath telescope and have a spectral resolution of 0.14 Å. We find no evidence for distinct emission features in the λ8542 lines, even for the most active chromosphere stars, but instead find that the line cores are filled in for active chromosphere stars compared to quiet chromosphere stars of the same spectral type. We derive chromospheric radiative loss rates in the A8542 line and find good correlations with chromospheric radiative loss rates in the Ca II H and K lines and Mg II h and k lines and with the Wilson-Bappu K-line index. Thus the λ8542 line is a good diagnostic of chromospheric activity. Computed λ8542 line profiles for the seven stars for which model chromospheres are available are not in as good agreement with the data as we would like, and for the three modeled giants the addition of macroturbulence cannot account for discrepancies in the line cores. We account for variability in the α Aur line profile as due to orbital motions of α Aur B, and we point out circumstellar features, indicating both outflowing and inflowing material, in six supergiants.