Meridional Circulation in Radiative Diffusion Zones of Rotating Stars

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Session 21 -- Stellar Spectroscopy, Atmospheres, Models, Intrinsic Variables, Theory, Part I
Display presentation, Tuesday, June 13, 1995, 9:20am - 6:30pm

[21.10] Meridional Circulation in Radiative Diffusion Zones of Rotating Stars

M.Maheswaran (U Wisconsin Centers)

(1968,MNRAS,140,93) for computing meridional circulation velocities is reviewed. The equations, after corrections are made for a misprint and a missing term, are improved to include different opacity laws. It is shown these equations can be used in radiative diffusion zones of uniformly rotating stars, where viscosity is negligible and the circulation speed is small compared with the rotation speed. Numerical results for different models of A stars are presented and discussed. It is seen that the opacity law influences the circulation pattern. For an upper main sequence star, the radiative diffusion zone, $Z$, is taken to be that part of the radiative envelope where radiation may be described by the diffusion equation. $Z$ is bounded by a surface, $S_1$, that is taken just outside the core-envelope boundary, and by a surface, $S_2$, at which the local diffusive form of radiation ceases to be valid. The boundary conditions used for the velocities are the same as in Maheswaran 1968, where the total flow of mass across each of $S_1$ and $S_2$ is zero, in a steady state. For the radiative regions outside $Z$, a more detailed treatment that includes viscosity, the coriolis force and turbulence together with boundary layer theory must be used, such as in Tassoul and Tassoul (1995, ApJ, 440, 789). However, there are some questions about the optical depth at which a boundary layer is established near the photosphere and how the radiation process should be treated in the surface region outside $Z$.

This work was supported by a UW Centers sabbatical leave grant.

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