Studies in stellar evolution. III. The calculation of model envelopes

Abstract

The formal theory underlying existing techniques for representing the superadiabatic layers in convective envelopes is re-examined. Particular emphasis is placed on the discussion of points of uncertainty and possible controversy. The analysis has been carried out in a form which permits the formulation of certain constants, the arbitrariness of whose values represents the inherent uncertainty in the theory. Parallel calculations based on different values of these constants lead to a quantitative evaluation of their effect upon evolutionary tracks in the Hertzsprung-Russell diagram. Marked effects result from uncertainties in the ratio of mixing length to scale height and possibly from inadequate knowledge concerning opacities at low temperatures.