Effects of Deviations from Local Thermodynamic Equilibrium on Solar Abundances

Abstract

Investigations of center-to-limb variations of curves of growth were carried out in order to detect effects of deviations from local thermodynamic equilibrium on solar abundances. The neutral stages of the elements Ca, Ti, V, Cr, Mn, Fe, and Co were considered. For three positions on the solar disk, = 1.0, 0.5, and 0.3, theoretical curves of growth were computed by the weighting-function method employing a new semi-empirical solar model and new partition functions. The observed curves of growth were constructed with the most reliable f-values available and with equivalent widths measured on three solar spectrum atlases of the McMath-Hulbert Observatory of the University of Michigan traced at the three values of . No systematic variation of the abundances from center to limb or from lower to higher excitation lines could be detected. This indicates that the assumption of local thermodynamic equilibrium does not introduce large errors in the solar abundances of the elements in the iron group. The high quality of the observational and theoretical data employed in this investigation should make possible reliable results for the abundances of the elements in the iron group. The choice of the absolute f-value scale is still very questionable, however, and completely trustworthy abundances cannot yet be obtained.