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R.V. Wagoner (Stanford University)
The gravitational-wave and accretion driven evolution of the angular velocity, core temperature, and (small) amplitude of an r-mode of neutron stars in low-mass X-ray binaries and similar systems is investigated. The conditions required for evolution to a stable equilibrium state (with gravitational wave flux proportional to average X-ray flux) are determined. In keeping with conclusions derived by Kaminker, Yakovlev and Gnedin (2002) from observations of neutron star cooling, the core neutrons are taken to be normal while the core protons and hyperons and the crust neutrons are taken to be singlet superfluids. The dominant sources of damping are then hyperon bulk viscosity (if much of the core has a density at least 2--3 times nuclear density) and (e-e and n-n scattering and possibly magnetic) shear viscosity within the core--crust boundary layer. It is found that a stable equilibrium state can be reached if the superfluid transition temperature of the hyperons is sufficiently small (\leq 2\times 109 K), allowing steady gravitational radiation (at a frequency f\cong 4/3P, with P the neutron star spin period) from Sco X-1 and several other neutron stars in low-mass X-ray binaries to be potentially detectable by the Advanced LIGO (and VIRGO) arrays.
This work was supported by NSF grant PHY-0070935.
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Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.