The empirical determination of the damping constants of Fraunhofer lines

Abstract

A systematic method is developed to determine the damping constant, γ, and its variation with optical depth, τ, in the solar photosphere, using the observed profiles of wings of Fraunhofer lines and their center-to-limb variation.

The method is applied to the 3s3P°−3p3D multiplet of carbon at 10,700 Å.

The resulting γ(τ) curve with its mean errors is shown in Fig. 2. This result can be explained by the usual assumption γ(τ) = γH, He(τ)+γe(τ), where γH, He is the contribution to the damping constant by collisional broadening by neutral particles; γe is due to the quadratic Stark effect of passing electrons. The “observed” values of the function γH,He(τ) agree perfectly with theoretical predictions. No theoretical predictions can yet be made for γe(τ) but the empirically derived values for this function are similar to values found from laboratory measurements for some lines of other elements, and look acceptable.