L. G. Henyey

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

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.

A NEW METHOD OF AUTOMATIC COMPUTATION OF STELLAR EVOLUTION

A method is described for obtaining time sequences of stellar models describing evolutionary changes. This method is a modified version of an earlier one described by Henyey, Wilets, Bohm, LeLevier, and Levee. The modifications involve the evaluation of all quantities at the same discrete points. The technique provides for coupling the interior integrations to those for model atmospheres based on mixing-length theory. The scope of the formalism is such as to provide for a wide range of calculations for spherically symmetric configurations in hydrostatic equilibrium. (auth)

THE EARLY PHASES OF STELLAR EVOLUTION

This paper is reproduced from Publ. Astron. Soc. Pac., Vol. 67, p. 154 - 160 (1955) to celebrate the centenary of the Publications. See also 065.165.

EVOLUTION OF MAIN-SEQUENCE STARS

Theoretical calculations of stellar evolution in the neighborhood of the main sequence were carried out with the UNIVAC computer at the Livermore Radiation Laboratory. The work was limited to masses ranging from l.5 to 30 x (mass of sun) and used a primeval composition of weight, consisting of 68 per cent hydrogen, 31 per cent helium, and 1 per cent heavy elements. Interpolation formulas for opacity, equation developed. Time sequences of stellar models were computed for the various masses for the time interval luring which the hydrogen content of the convective cores decreased to essentially zero. The time variation of the relevant parameters describing the stellar interior are given in graphic and tabular form. Tracks for the various masses are exhibited in the colormagnitude diagram. A comparison of curves of constant age with cluster diagrams is made, and estimates of cluster ages are given. (auth)