Good Vibrations: Reliable Oscillation Frequencies for Rapidly Rotating Stars

Details Good Vibrations: Reliable Oscillation Frequencies for Rapidly Rotating Stars Good Vibrations: Reliable Oscillation Frequencies for Rapidly Rotating Stars

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.2501l&link_type=abstract

American Astronomical Society, AAS Meeting #211, #25.01; Bulletin of the American Astronomical Society, Vol. 39, p.775

Astronomy and Astrophysics

Astronomy

Scientific paper

Certain types of main sequence variable stars are known to have some rapidly rotating members. Rotation can change the interior properties of these stars, and hence affect the oscillation modes themselves. Current techniques for linear mode calculations in rotating stars treat the effects of stellar rotation as a perturbation to the structure of the star, which in turn produces a perturbation on the eigenfrequency. In slowly rotating stars, these methods work well, and the eigenfunction can be accurately modelled using a single spherical harmonic. As the rotation rate increases, the individual modes can be expressed as a sum of spherical harmonics, but the exact number needed is unknown. It is well known that the perturbation methods, which generally model the mode using a single spherical harmonic, break down as the stellar rotation velocity approaches some threshold velocity, but there is little or no agreement on where this threshold actually is. We use 2D stellar models and a 2D finite difference integration of the linearized pulsation equations to calculate non-radial oscillations. This finite difference approach allows us to directly calculate the pulsation modes for a distorted rotating star with both uniform and differential rotataion, without treating the rotation as a perturbation. We are also able to include multiple basis functions (spherical harmonics) in each mode calculation. Using these methods, we have investigated the effects of rotation velocity and number of basis functions on the calculated eigenfrequencies and eigenfunctions. We find that 1 basis function remains reasonable up to a rotation rate around 300km s-1 (35 % of Ωcrit)for the radial fundamental mode of a 10 M&sun; star, but can fail as rotation rates as low as 90km s-1 for the 2H mode or l = 2 p2 mode, based on the eigenfrequencies alone.

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