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

Free access article

Issue		A&A Volume 428, Number 1, December II 2004


Page(s)		171 - 179
Section		Stellar structure and evolution
DOI		http://dx.doi.org/10.1051/0004-6361:20041202

A&A 428, 171-179 (2004)
DOI: 10.1051/0004-6361:20041202

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

I. W. Roxburgh^{1, 2}

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 $\Omega$ 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 $1, 2, 5, 10~M_\odot$ with a range of angular velocities up to break up. The models have a composition X=0.70, Z=0.02 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 $R_{\rm p}$ 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 $R_{\rm e}$ . Due to the contribution of the gravitational multipole moments the parameter $\Omega^2 R_{\rm e}^3/GM$ can exceed unity in very rapidly rotating stars and $R_{\rm e}/R_{\rm p}$ can exceed 1.5.

Key words: stars: interiors -- stars: rotation

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