Assigned ID: 263 ----- Submission 1 (Fri Jan 21 17:57:49 GMT 2005) ----- The Crab pulsar is the prototypical young neutron star and is one of the most studied extrasolar objects. It provides the foundation for our understanding of pulsar spin-down, magnetospheric physics, and energy loss through relativistic winds. With an indisputable supernova association and a known age, it is also an ideal laboratory to study core-collapse supernovae and neutron star birth kicks, but useful constraints on all of these questions require accurate distance and velocity measurements. However, despite the preeminence of the Crab these quantities are poorly known: the distance to the supernova remnant has been estimated with 30% uncertainties and there are no direct measurements of the pulsar's distance, while its proper motion has been estimated from a crude analysis of saturated HST data spanning only two years. Here we propose to analyze the full set of existing HST/WFPC2 data on the Crab pulsar, spanning seven years and using multiple filters. We will fully characterize the measurement uncertainties, including the effects of saturation, and determine a precise proper motion. We will also attempt to measure an astrometric parallax to the source, or determine the minimum additional data necessary to enable such a measurement.

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