The Excitation Equilibrium in the Solar Corona and Non-Maxwellian Electron Distributions

We demonstrate the influence of an electron non-Maxwellian distribution function on the collisional excitation coefficient and, as an example, on the excitation equilibrium of Fe XIV in the solar corona. The results can be used for specific applications in the solar corona, especially in the active corona, where deviations from Maxwellian distribution can be significant.

Accurate Spectroscopic Surface Gravities for 8 Sub-Giants

Logarithmic surface gravities between 2.9 and 3.8 (cgs) have been determined for eight G8IV-K2III stars from the analysis of pressure broadened wings of strong metal lines. Comparisons with trigonometrically determined surface gravities give support to the spectroscopic results. A thorough and rather conservative error analysis suggests that the errors are smaller than about 30% and confirms that the method is very insensitive to uncertainties in the fundamental stellar atmospheric parameters. Surface gravities of α Cen A and B and of Arcturus have also been obtained. Chemical abundances have been derived for 12 elements from Na to Ni, and for five heavier elements from Y to Nd have tentative abundances been derived from a single line of each element. Effective temperatures in the photometric system of Frisk (1983) are found to be consistent with spectroscopic temperatures from the excitation equilibrium of Fe I. Surface gravities determined from the ionization equilibria of Fe and Si are found to be systematically lower than the strong line gravities, which may be an effect of errors in the model atmospheres, or departures from LTE in the ionization equilibria.