Continuous frequency spectrum of the global hydromagnetic oscillations of a magnetically confined mountain on an accreting neutron star |
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Authors: | M Vigelius A Melatos |
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Institution: | School of Physics, University of Melbourne, Parkville, VIC 3010, Australia |
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Abstract: | We compute the continuous part of the ideal-magnetohydrodynamic (ideal-MHD) frequency spectrum of a polar mountain produced by magnetic burial on an accreting neutron star. Applying the formalism developed by Hellsten & Spies, extended to include gravity, we solve the singular eigenvalue problem subject to line-tying boundary conditions. This spectrum divides into an Alfvén part and a cusp part. The eigenfunctions are chirped and anharmonic with an exponential envelope, and the eigenfrequencies cover the whole spectrum above a minimum ωlow. For equilibria with accreted mass 1.2 × 10?6? M a/M⊙? 1.7 × 10?4 and surface magnetic fields 1011? B */G ? 1013, ωlow is approximately independent of B * , and increases with M a. The results are consistent with the Alfvén spectrum excited in numerical simulations with the zeus-mp solver. The spectrum is modified substantially by the Coriolis force in neutron stars spinning faster than ~100 Hz. The implications for gravitational-wave searches for low-mass X-ray binaries are considered briefly. |
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Keywords: | accretion accretion discs stars: magnetic fields stars: neutron pulsars: general |
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