2-dimensional models of rapidly rotating stars

Abstract

Aims.We show how to construct 2-dimensional models of rapidly rotating stars in hydrostatic equilibrium for any Ω(r,θ), given the density ρ_m(r) along any one angle θ_m. If the hydrogen abundance X_m(r) is given on θm then the adiabatic exponent Γ_1(r,θ) can by determined, yielding a self consistent acoustic model that can be used to investigate the oscillation properties of rapidly rotating stars. Methods: .The system of equations governing the hydrostatic structure is solved by iteration using the method of characteristics and spectral expansion, subject to the condition that ρ(r,θ)=ρ_m(r) on θ=θ_m. Γ_1(r,θ) is calculated from the equation of state under the assumption that X(r,θ_m)=X_m(r) and is constant on surfaces of constant entropy. Alternatively Γ1 can be approximated by taking X constant in the equation of state and equal to the surface value. Results: .Results are presented for an evolved main sequence star of 2~M_ȯ with the angular velocity a function only of radius Ω=Ω(r), evolved to a central hydrogen abundance of X_c=0.35. The model is first calculated using a spherically averaged stellar evolution code, where the averaged centrifugal force 2Ω2 r/3 is added to gravity. The resulting ρ_m(r), X_m(r) are then used as input to determine the 2-dimensional model. Conclusions: .The procedure described here gives self consistent hydrostatic and acoustic models of rapidly rotating stars for any Ω(r,θ).