Krivicic, Jasna (2012) Stellar evolution code with rotation. [Ph.D. thesis]
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There is a lot of observational and theoretical evidence that rotation crucially affects stellar structure and stellar evolution in particular for massive stars. Rotation influences the life of stars in several ways. For instance, centrifugal forces reduce the effective gravitational attraction, but also certain mixing processes of chemical elements can be induced by rotation, and mass loss can be altered. Within this thesis we describe the implementation of differential rotation in a stellar evolution code. Because of theoretical considerations stars are assumed to establish a rotation law with constant angular velocities on isobaric surfaces (shellular rotation). In this case the one-dimensional, spherical stellar structure equations can be modified to account for differential rotation including structural deformations of the star. By this approach the description of a stellar object is formally kept one-dimensional and one can utilize the numerical infrastructure of an existing ``nonrotating'' stellar evolution code. As a basis we use the Padova stellar evolution code, which is prepared and tested by us for the purposes of this work. In this thesis we present details about the development of additional numerical modules for treating rotation and how these extensions are implemented in an existing code. Moreover, we show the first results of our new implementation, which also includes a prescription of mass loss taking into account the effects of rotation. We discuss the obtained evolutionary tracks for rotating massive stars and compare our findings with results available in the literature. As far as a comparison is meaningful because of different stellar models and different degrees of sophistication in the modelling of additional physical processes, we observe the same effects of rotation as have been reported in the literature. For instance, on the main sequence the effective temperature is reduced for rotating models with respect to their nonrotating counterparts. Rotating stars essentially mimic the behavior of nonrotating but slightly less massive stars. Our work explores the effects of rotation for varied stellar masses, varied chemical compositions and different initial rotation rates. In addition, the role of overshooting in rotating models is investigated. Finally, we indicate plans for future work, which includes numerical developments, the consideration of further physical processes as well as the computation and detailed analysis of a larger set of models
Esistono numerose evidenze sia sperimentali che teoriche riguardanti l'importanza della rotazione sulla struttura ed evoluzione delle stelle e in particolare di quelle massicce.
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