Stellar model chromospheres. X - High-resolution, absolute flux profiles of the CA II H and K lines in stars of spectral types F0-M2

Abstract

We present 120 mÅ resolution spectra of the cores and wings of the Ca II H and K lines in 43 stars covering a wide range of spectral type and luminosity class. These spectra were obtained with the KPNO 4 m echelle spectrograph and blue image tube, and are calibrated in absolute surface flux units using Willstrop's narrow-band photometry and the Barnes and Evans relations for stellar angular diameters. We estimate an uncertainty of ±15% in our flux scales. We derive chromospheric radiative loss rates in the H and K lines, and discuss trends in these loss rates with effective temperature for dwarfs, giants, and supergiants. We compare these loss rates with similar rates for the Mg II h and k lines, and discuss the doublet line ratios for H and K. The monochromatic surface fluxes for different features in the H and K lines are presented. From the surface fluxes at K<SUB>1</SUB> we derive the radiation temperature T<SUB>R</SUB>(K<SUB>1</SUB>). The T<SUB>R</SUB>(K<SUB>1</SUB>)/T<SUB>eff</SUB> ratio is lower in giants than in dwarfs, as predicted by partial redistribution calculations, and this ratio appears to be an empirical age indicator among dwarfs. Asymmetries in the K line profile provide evidence for a solar-type supergranulation flow pattern in F5-K5 dwarfs and perhaps also in G and early K supergiants. Measurements of line widths at H<SUB>1</SUB>, K<SUB>1</SUB>, and K<SUB>2</SUB> are presented, together with FWHM data for the H and K lines. We find rough agreement between the measured K1 widths and the gravity and chromospheric heating rate dependences in the scaling law proposed by Ayres. Finally, we present data on emission lines in the wings of H and K, and discuss chromospheric radiative loss rates in the HE line compared with loss rates in the H and K lines.