AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 52. White Dwarfs, Neutron Stars and Pulsars
Display, Tuesday, June 1, 1999, 10:00am-7:00pm, Southeast Exhibit Hall

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[52.08] Radio Pulsar Evidence for Quaking Neutron Stars

L. M. Franco (Univ. of Chicago \& LANL), B. Link (Montana State Univ. \& LANL), R. I. Epstein (Los Alamos National Lab)

The Crab and other pulsars suffer sudden and permanent increases in their spin-down rates, suggesting that the torques upon them increase in steps. Torque changes could come about as a consequence of "starquakes" occurring as the star spins down and its rigid crust becomes less oblate. We present an update of our study of the evolution of strain in the crust, the initiation of starquakes, the effects on the magnetic field structure and the observable consequences for neutron star spin-down. We find that the stellar crust begins breaking at the equator, forming a fault along which matter flows to higher latitudes to reduce the equatorial circumference. Magnetic stresses force an asymmetric redistribution of matter which in turn misaligns the angular momentum and spin axes. The ensuing damped precession leads to a new equilibrium state with an increased angle between rotation and magnetic axes. The change in alignment angle could increase the external torque and produce the observed permanent increase in the spin-down rate.

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