EFFECTS OF DIFFERENTIAL ROTATION AND TIDAL DISTORTION ON THE STRUCTURE AND OSCILLATIONS OF STARS

Abstract

The present thesis deals with the problems of equilibrium structure and small oscillations of differentially of the stars. The problem of structure and oscillations have practical importance in Astrophysics. Observations have shown that there are certain variable stars which are rotating about their axis. This rotation may be a solid body rotation or a differential rotation in which different parts of the star are rotating with different angular velocities (for instance 'Further Evidence For Differential Rotation in V1057 Cygni', Allan D. Welty et al., Ap.J., Vol. 349, pp.328-334, 1990). The theoretical models of such rotating stars get distorted by rotational forces. Also some of the stars are observed as members of binary and multiple stellar systems. Equilibrium models of such stars get distorted by the tidal effects alone if the star is not rotating and by the rotational and tidal effects if the star in the binary, or multiple system is rotating as well. Some of the rotating stars and stars in binary systems are also known to be variable stars (for instance 53 Per, 12 Lac, 1 Mon and 16 Lac etc.). Because of the gravitational pull of the companion star and the effect of rotation, the periods of oscillations of such variable stars get distorted by the tidal and rotational effects. Some of the observed phenomena of such rotating stars and stars in binary systems are attributed to their small periodic oscillations. In order to understand properly, the observed phenomena of such variable stars as well as to understand the problems of stability of rotating stars and stars in binary systems, it is, therefore, necessary to investigate the theoretical problems of small oscillations of rotationally distorted as well as rotationally and tidally distorted gaseous spheres.