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On the Structure and Properties of Differentially Rotating Main-Sequence Stars in the 1-2 M_sun Range  

Travis S Metcalfe   Submitted: 2007-04-11 08:25

We conduct a systematic examination of the properties of models for chemically homogeneous, differentially rotating, main-sequence stars of mass 1-2 M_sun. The models were constructed using a code based on a reformulation of the self-consistent field method of computing the equilibrium stellar structure for a specified conservative internal rotation law. The code has recently been upgraded with the addition of new opacity, equation of state, and energy generation routines, and a mixing-length treatment of convection in the outer layers of the stellar interior. Relative to nonrotating stars of the same mass, these models all have reduced luminosities and effective temperatures, and flattened photospheric shapes (i.e., decreased polar radii) with equatorial radii that can be larger or smaller, depending on the degree of differential rotation. For a fixed ratio of the axial rotation rate to the surface equatorial rotation rate, increasingly rapid rotation generally deepens convective envelopes, shrinks convective cores, and can lead to the presence of a convective core (envelope) in a 1 M_sun (2 M_sun) model, a feature that is absent in a nonrotating star of the same mass. The positions of differentially rotating models for a given mass M in the H-R diagram can be shifted in such a way as to approximate the nonrotating ZAMS over ranges in luminosity and effective temperature that correspond to a mass interval between M and about 0.7 M. We briefly note a few of the implications of these results, including (i) possible ambiguities arising from similarities between the properties of rotating and nonrotating models of different masses, (ii) a reduced radiative luminosity for a young, rapidly rotating Sun, (iii) the nuclear destruction of lithium and other light metallic species in the layers beneath an outer convective envelope, and (iv), the excitation of solar-like oscillations and the operation of a solar-like hydromagnetic dynamo in some 1.5-2 M_sun stars.

Authors: K. B. MacGregor, Stephen Jackson, Andrew Skumanich, T. S. Metcalfe
Projects: None

Publication Status: ApJ (accepted)
Last Modified: 2007-04-11 10:22
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On the Structure and Properties of Differentially Rotating Main-Sequence Stars in the 1-2 M_sun Range

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