Statistics – Computation
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt.........7h&link_type=abstract
Ph.D. Thesis Yale Univ., New Haven, CT.
Statistics
Computation
8
Massive Stars, Stellar Evolution, Stellar Mass, Stellar Models, Stellar Rotation, Helium, Main Sequence Stars
Scientific paper
The Yale Rotating Evolution Code has been modified to allow for the computation of models of massive stars. Theoretical evolutionary sequences have been generated for a 15 M solar magnitude star from the ZAMS to core helium exhaustion with a variety of physical assumptions: (1) no convective overshoot, mass loss, or rotation, (2) convective overshoot only, by amounts 0.1, 0.2, and 0.35 Hp, (3) mass loss only, for log Teff greater than 4.1 at rates given by the parameterization of Waldon and for log Teff less than 4.1 at rates given by Reimers' formulation, (4) mass loss and overshoot by 0.1 Hp, (5) no overshoot of mass loss, but rotation without instabilities, and (6) no overshoot or mass loss, but full rotation. An additional sequence, (7) mass loss and full rotation, was run to just past core helium ignition. Models were also run for 20, 25, and 20 M solar magnitude stars using the same physical assumptions, but all of these sequences were terminated just after core helium ignition due to time constraints. The non-rotating models agree qualitatively with other models found in the literature. The addition of only rotational distortion has little discernable effect on the models, while the full treatment of rotation results in additional mixing and theoretical tracks that are similar to models with small amounts of convective overshoot. Models which include only rotation have fair agreement with the observed main sequence surface rotation velocities, but rotate too rapidly during the post-main sequence phases. The addition of mass loss at the given rates helps this problem somewhat but does not appear to completely resolve it. Neither the non-rotating models nor the rotating models provide full agreement with the terminal-age main sequence band used by Maeder and Meynet: this may be indicative that additional mixing processes are necessary or that a more recent TAMS, such as that of Stothers, should be used.
Howard Jamie Michael
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