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S. Chatterjee (NRAO)
The measurement of distances is a fundamental problem in astronomy. Parallaxes and proper motions of pulsars provide model-independent estimates of their distances and velocities, allowing us to probe the physics of neutron stars, constrain core collapse phenomena in supernovae, and investigate the distribution of matter in the interstellar medium. Here we present high-precision measurements of the trigonometric parallaxes and proper motions of three radio pulsars using the NRAO Very Long Baseline Array, and discuss how they have been used to investigate the interstellar medium, as well as the birth sites, cooling curves, and velocity distribution of neutron stars.
Bow shocks and pulsar wind nebulae probe the interaction of neutron star relativistic winds with the interstellar medium. We utilize scaling laws derived for bow shock nebulae, in combination with estimates of neutron star distances and velocities, to extract information about the interstellar medium. The spectacular Guitar nebula, produced by a high velocity but otherwise unremarkable neutron star, was observed at two epochs with the Hubble Space Telescope. We report time evolution in the position and morphology of the nebula, and infer the existence of small scale density fluctuations in the interstellar medium.
Increases in the sample of precise astrometric measurements will enable many such scientific applications: we introduce an ongoing project with the Very Long Baseline Array, which is expected to at least double the number of measured pulsar parallaxes in the next two years.
This work was supported in part by NSF grants AST 9819931 and AST 0206036 to Cornell University. NRAO is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. Observations made with the NASA/ESA Hubble Space Telescope were obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.