Gravitational Radiation from Nonaxisymmetric Rotational Instabilities in a Rotating Star
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**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.

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