Main sequence for rotating stars of intermediate mass (Q1820605)

We have investigated the evolutionary behaviour of intermediate mass Population I stars, assuming two different rates of rotation at the threshold of stability. In the first part of the study, stars are assumed to start with a critical rotation (fast rotation model) and to progress to the point of rotational instability. The stars evolve by losing mass and become rotationally unstable before they reach the zero-age main sequence. It is argued that multiple star systems might be formed through the evolution of rapidly rotating stars. An expression for the rotational mass loss rate is derived as a function of the physical parameters of stars. In the second part of the study, stars are assumed to rotate at a rate below the critical value (slow rotation model). The evolution of slowly rotating stars is followed as far as zero-age main sequence on the theoretical Hertzsprung-Russell diagram and compared with that of normal stars. The evolutionary paths are found to be more or less similar to those of normal stars; but their positions on the main sequence are characterized by effective temperatures and luminosities lower than those of normal stars. The zero-age main-sequence times of these stars are longer than those of normal stars. The rotational rates obtained for the zero-age main sequence are in good agreement with observed values.