The Effect of Differential Rotation on the Internal Structure of Low Mass Stars.
Abstract
Axisymmetric, differentially rotating main sequence models for stars of 0.9M \and homogeneous composition (X = 0.7999, Z = 0.0001) have been constructed. The effects of rotation on the internal structure of the stellar models have been studied with different amounts and different distributions of angular momentum. The angular velocity distribution is assumed to be constant on surfaces of constant density. It is found that differential rotation produces significant effects on the interior of the models. The most noteworthy feature is the decrease in luminosity due to rotation. The change in bolometric magnitude for a moderatelyrotating model with (VBAR) (,W) (VBAR) (TURNEQ) 0.037 is about 0.53 mag.; for a rapidly rotating model with (VBAR) (,W) (VBAR) (TURNEQ) 0.073, it is about 1.05 mag. Thus the stellar massluminosity relation would be substantially affected by differential rotation. Differential rotation also causes a large decrease in central pressure, temperature and density. For a given total angular momentum, a change in the distribution of angular momentum is found to have mild effects on the central conditions and negligible effect on the liminosity; the calculated equatorial velocity depends strongly on the rotation law. Uniform rotation produces a large distortion of the stellar surface. Differential rotation where angular velocity increases inward can produce an extremely distorted central region, while the surface region is less affected. In the theoretical HR diagram, uniform rotation moves the models away from and above the zeroage, zero rotation main sequence (ZRMS). Differential rotation displaces the models downward almost parallel to the ZRMS. For rapid central rotation or large amounts of angular momentum, the model can be displaced even below the ZRMS. The main sequence lifetimes of the rotating models, estimated from the stellar mass and luminosity, can be increased by more than a factor of 3 over the lifetimes of nonrotating stars of the same mass, and as much as 30% over the lifetimes of lower mass, nonrotating stars with comparable luminosities.
 Publication:

Ph.D. Thesis
 Pub Date:
 1980
 Bibcode:
 1980PhDT.........5L
 Keywords:

 Physics: Astronomy and Astrophysics;
 Stellar Interiors;
 Stellar Luminosity;
 Stellar Mass;
 Stellar Rotation;
 Stellar Structure;
 Angular Momentum;
 Main Sequence Stars;
 Variable Stars;
 Astrophysics