2-dimensional models of rapidly rotating stars I. Uniformly rotating zero age main sequence stars

¹ Astronomy Unit, Queen Mary, University of London, Mile End Road, London E1 4NS, UK e-mail: I.W.Roxburgh@qmul.ac.uk
² LESIA, Observatoire de Paris, Place Jules Janssen, 92195 Meudon Cedex, France

Received: 30 April 2004
Accepted: 6 August 2004

Abstract

We present results for 2-dimensional models of rapidly rotating main sequence stars for the case where the angular velocity Ω is constant throughout the star. The algorithm used solves for the structure on equipotential surfaces and iteratively updates the total potential, solving Poisson's equation by Legendre polynomial decomposition; the algorithm can readily be extended to include rotation constant on cylinders. We show that this only requires a small number of Legendre polynomials to accurately represent the solution. We present results for models of homogeneous zero age main sequence stars of mass  with a range of angular velocities up to break up. The models have a composition  and were computed using the OPAL equation of state and OPAL/Alexander opacities, and a mixing length model of convection modified to include the effect of rotation. The models all show a decrease in luminosity L and polar radius R_p with increasing angular velocity, the magnitude of the decrease varying with mass but of the order of a few percent for rapid rotation, and an increase in equatorial radius R_e. Due to the contribution of the gravitational multipole moments the parameter  can exceed unity in very rapidly rotating stars and  can exceed 1.5.