Gravitational Radiation from Nonaxisymmetric Rotational Instabilities in a Rotating Star
Session 48 -- Degenerate Stars and Pulsars
Display presentation, Thursday, June 15, 1995, 9:20am - 4:00pm

## [48.12] Gravitational Radiation from Nonaxisymmetric Rotational Instabilities in a Rotating Star

J. L. Houser, J. M. Centrella (Drexel U.)

We present 3D numerical simulations of the non-axisymmetric dynamical bar mode instability in a rotating star, as well as the resulting gravitational radiation waveforms. This instability may operate during the collapse of rapidly rotating stellar cores or in white dwarfs spun up by accretion. Using a smoothed particle hydrodynamics (SPH) code, we created 7 models, varying the number of particles used to represent the fluid, the artificial viscosity, and the type of initial model distribution. We here compare the resulting growth rates, bar rotation speeds, mass and angular momentum distributions, and gravitational radiation quantities. The star was modeled as a polytrope with index $n = 3/2$, and starts out with $T_{\rm rot}/|W| \approx 0.30$, where $T_{\rm rot}$ is the rotational kinetic energy and $|W|$ is the gravitational potential energy. The code assumes a Newtonian gravitational field, and the gravitational radiation is calculated in the quadrupole approximation.

The conclusion of this analysis shows that all models deform into a bar shape and shed mass in the form of a two-armed spiral pattern. Typically, $\sim 10\%$ of the original mass and $\sim 30\%$ of the original angular momentum are transferred to the arms, which eventually spread into a uniform quasi-Keplerian disk. The resulting central core rotates with $T_{\rm rot}/|W| \approx 0.25$, just below the dynamical instability point. Finally, the amplitudes of the gravitational wave quantities increase as the number of particles increases. Higher resolution runs, or models with non-equal-mass particles are needed to achieve convergence in these quantities.