Scaling of oscillation frequencies in rotating stars

TL;DR

This study investigates how oscillation frequencies in rotating stars scale with mass and rotation, confirming that the root-mean-density relation applies to p modes and revealing similar scaling for g modes, aiding stellar modeling.

Contribution

It demonstrates that frequency scaling relations hold for rotating stars of the same shape, extending the root-mean-density relation to more realistic stellar models.

Findings

Scaling relations exist among oscillation frequencies for models with the same shape.

P modes follow the root-mean-density period relation in rotating stars.

G modes scale with stellar properties outside the convective core.

Abstract

Properties of stars undergoing pulsation such as the well known root-mean-density scaling relation can be useful when trying to match the observed properties of a particular star. It is often assumed that this relation is valid for p mode frequencies in rotating stars. To examine the change in frequency with rotation and mass, we have studied oscillation frequencies of two-dimensional uniformly rotating zero-age main sequence stellar models in the delta Scuti mass range. We identified 370 p and g axisymetric modes for non-rotating models and then traced the changes in their frequencies as the rotational velocity was increased. For each mass we considered a rotation sequence of ten models, with the largest rotation rate being about 200 km s$^{-1}$. We constrained the models to have the same surface shape, which can be characterized for uniform rotation by the ratio between the polar and the equatorial radii. We find that scaling relationships exist among the oscillation frequencies of the same mode for different masses when the models have the same shape. For p modes, this scaling closely follows the period root-mean-density relation found in spherical stars. The g modes also scale between models of the same shape, with the scaling reflecting the change in properties outside the convective core as the stellar mass increases. These scaling relationships can be particularly useful in finding specific stellar models to match the oscillation frequencies of individual stars.