Observing Millisecond and Binary Pulsars.

The spin-up of a slowly rotating neutron star by mass accretion from a companion object creates more than just a fast pulsar. The so-called "recycled" pulsars, a class including millisecond pulsars and most if not all pulsars in binary systems and globular clusters, differ in a number of interesting and important ways from their slower cousins. Typical pulsars are young objects, thousands to tens of millions of years old, whereas billion year old recycled pulsars are the living fossils of our galaxy. The magnetic fields of recycled pulsars are often a thousand times weaker than those of young pulsars. But most importantly for the experimental astrophysicist, recycled pulsars are extremely accurate flywheels, seemingly free of the random timing noise of youth. And as ideal clocks, they provide unique probes of their environments, the interstellar medium, and the universe itself. I have installed a timing system at the Very Large Array, primarily to observe recycled pulsars. With it I have made preliminary observations of a number of fast pulsars. Long term timing of an array of millisecond pulsars can set strong limits on the cosmological background of very low frequency gravitational radiation, predicted by several models of the early universe, and allows very precise astrometrical and metrological measurements. I have made observations of the eclipsing binary pulsar in Terzan 5, at both the VLA and Green Bank, to investigate the mechanism by which a pulsar may evaporate a companion star. First epoch observations of four other binary pulsars will, in the next few years, lead to new information on neutron star masses, and perhaps new limits on the time-rate-of -change of Newton's constant, G. Finally, I have constructed a multiplying polarimeter, and made polarization and average profile measurements of several millisecond pulsars with the Arecibo telescope, in an attempt to understand the similarities and differences of the radio emissions from recycled and ordinary pulsars. One appendix describes the polarimeter design, and two more briefly describe other investigations: new limits on certain non-symmetric gravity theories from pulsar measurements, and a new relationship between pulse shape and observing frequency.