Semiempirical upper photosphere models: The Sun (G2 V) and Procyon (F5 IV-V)

A general method is described for inferring the average upper photosphere temperature structure of a late-type star using calibrated observations of resonance line wings and a partial coherent scattering approximation. This approach is applied to two problems: A comparison of the excess radiative losses from the upper photospheres of the Sun and Procyon is made by ''calibrating'' observed profiles of the Ca ii K line wings relative to Kurucz's radiative equilibrium models for tau5000approximately-greater-than0.1. Deviations of the empirical fluxes from the synthesized profiles are interpreted as evidence for departures from radiative equilibrium in the surface layers of both stars (tau5000<0.1). Temperature enhancement models are constructed to account for these deviations, and estimate rough upper limits to the corresponding excess radiative losses by considering only the effect of the Planck function differences on the H- radiative loss rate. An accurate determination of the Mg ii k to Ca ii K emission core flux ratio is obtained for the Sun and Procyon by calibrating the Mg ii k wings relative to the Ca ii K wings in each star. Results support Ulmschneider's speculation that short-period acoustic waves heat the lower chromosphere after being heavily damped in the upper photosphere. In addition, Procyon's chromospheric temperature gradient is probably shallower than the Sun's, although the acoustic energy dissipation in Procyon's upper photosphere is very likely larger, in accord with de Loore's application of the Lighthill-Proudman theory