F. Espinosa Lara, M. Rieutord
This work aims at presenting the first two-dimensional models of an isolated rapidly rotating star that include the derivation of the differential rotation and meridional circulation in a self-consistent way. We use spectral methods in multidomains together with a Newton algorithm to determine the steady state solutions including differential rotation and meridional circulation for an isolated non-magnetic rapidly rotating early-type star. In particular we devise an asymptotic method for small Ekman numbers (small viscosities) that removes the Ekman boundary layer and lifts the degeneracy of the inviscid baroclinic solutions. For the first time, realistic two-dimensional models of fast rotating stars are computed with the actual baroclinic flows that predict the differential rotation and the meridional circulation for intermediate-mass and massive stars. These models nicely compare with available data of some nearby fast rotating early-type stars like Ras Alhague (alpha Oph), Regulus (alpha Leo) and Vega (alpha Lyr). It is shown that baroclinicity drives a differential rotation with a slow pole and a fast equator and a fast core and a slow envelope. The differential rotation is found to increase with mass, with evolution (here measured by the hydrogen mass fraction in the core) and with metallicity. The core-envelope interface is found to be a place of strong shear where mixing will be efficient. Two-dimensional models offer a new view of fast rotating stars especially of their differential rotation, which turns out to be strong at the core-envelope interface. They also offer more accurate models for the interpretation of interferometric, spectroscopic and asteroseismologic data of early-type stars.
View original:
http://arxiv.org/abs/1212.0778
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