Laboratory Spectroscopy in Support of Studies of Metal-Poor Galactic Halo Stars

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AST-0506453Stephen ThorsettUniversity of California-Santa CruzPulsar InterferometryABSTRACTThe Milky Way contains between 100 million and one billion neutron stars, left behind after thesupernova explosions that distributed heavy elements throughout the Galaxy. Understanding thedistribution and properties of these stars is important for understanding Galactic chemical evolution,as well as for constraining the dynamics of supernova explosions and for illuminating the formationand life-cycles of various type of exotic compact binary systems.The most direct constraints on the neutron star distribution come from measurements of parallaxesand proper motions. In most cases, these measurements can be made only for the subclass ofneutron stars that are luminous at radio wavelengths: the radio pulsars. Even then, the closest radiopulsars are a hundred times the distance of the closest stars, and the effects of parallax and propermotion are correspondingly smaller. Only about 1% of pulsars have measured parallaxes and onlyabout 10% of pulsars have even crudely measured proper motions.Here, Thorsett and Dewey will continue their highly successful interferometry program, using theVery Large Array and the Very Long Baseline Array to make very precise astrometricmeasurements of a large sample of pulsars and address several important questions. Theinvestigation will, over the next three years, measure the birth velocity distribution of neutron starswith sufficient accuracy to constrain both the high and low velocity tails (needed to understandsupernova asymmetries and retention of neutron stars in globular clusters, respectively), and willimprove understanding of local pulsar distances and the local pulsar birthrate. This plan is basedprimarily on observations that are either underway or already approved.The investigations will include student training and support, with project data forming the basis of aPh.D. thesis. The student and the principle investigators will also maintain formal connections andparticipate in activities with the Exploratorium science museum and the COSMOS summerprogram. Co-investigator Dewey is also Education and Public Outreach Director for the UCSCbranch of Calspace, providing further outreach opportunities.External science investigations will also be enabled by both web and traditional publication of thedata gathered here. These include identification of the primary target lists for The Gamma-ray LargeArea Space Telescope and other satellite missions, and interpretation of multiwavelength pulsaremission data. Comparison of the local pulsar birthrate to the massive star birthrate, constrains theproperties of the progenitors of Type II supernovae. Pulsar velocity measurements not onlyconstrain models of their birth events, and are important input parameters to population synthesisstudies of binary systems. The observations made to identify calibration sources for the Very LongBaseline Array surveys comprise a large survey sample of 21-cm snapshots of extragalactic sources.