Showing papers by "John Reynolds published in 2005"

VLBI Observations of Southern Hemisphere ICRF Sources. II. Astrometric Suitability Based on Intrinsic Structure

Abstract: We present 8.4 GHz very long baseline interferometry (VLBI) observations of 48 southern hemisphere extragalactic sources from the International Celestial Reference Frame. These are the second in a series of observations intended to image all such sources in the southern hemisphere at milliarcsecond resolution and bring the total number of observed sources to 111. We use these data, together with previously published data, to quantify the magnitude of the expected effect of intrinsic source structure on astrometric bandwidth synthesis VLBI observations by calculating a structure index for the sources; the structure index yields an estimate of their astrometric quality. Approximately 35% of sources in our sample have a structure index indicative of compact or very compact structures. The remaining two-thirds of our sources are less compact and should probably be avoided in astrometric and geodetic VLBI experiments requiring the highest accuracy unless intrinsic source structure can be accounted for in the astrometric/geodetic analysis.

On the dynamics of the ABDoradus system

Abstract: We present an astrometric analysis of the binary systems ABDorA /ABDorC and ABDorBa / ABDorBb. These two systems of well-known late-type stars are gravitationally associated and they constitute the quadruple ABDoradus system. From the astrometric data available at different wavelengths, we report: (i) a determination of the orbit of ABDorC, the very low mass companion to ABDorA, which confirms the mass estimate of 0.090Msun reported in previous works; (ii) a measurement of the parallax of ABDorBa, which unambiguously confirms the long-suspected physical association between this star and ABDorA; and (iii) evidence of orbital motion of ABDorBa around ABDorA, which places an upper bound of 0.4Msun on the mass of the pair ABDorBa / ABDorBb (50% probability). Further astrometric monitoring of the system at all possible wavelengths would determine with extraordinary precision the dynamical mass of its four components.

Testing GR with the Double Pulsar: Recent Results

Abstract: M. Kramer, D.R. Lorimer, A.G. Lyne, M. McLaughlin University of Manchester, Jodrell Bank Observatory, UK M. Burgay, N. D’Amico, A. Possenti INAF Osservatorio Astronomica di Cagliari, Italy F. Camilo Columbia Astrophysics Laboratory, Columbia University, USA P.C.C. Freire NAIC, Arecibo Observatory, USA B.C. Joshi NCRA, Pune, India R.N. Manchester, J. Reynolds, J. Sarkissian Australia Telescope National Facility, CSIRO, Australia I.H. Stairs, R. D. Ferdman Department of Physics and Astronomy, University of British Columbia, Canada

Testing GR with the Double Pulsar: Recent Results

Abstract: This first ever double pulsar system consists of two pulsars orbiting the common center of mass in a slightly eccentric orbit of only 2.4-hr duration. The pair of pulsars with pulse periods of 22 ms and 2.8 sec, respectively, confirms the long-proposed recycling theory for millisecond pulsars and provides an exciting opportunity to study the works of pulsar magnetospheres by a very fortunate geometrical alignment of the orbit relative to our line-of-sight. In particular, this binary system represents a truly unique laboratory for relativistic gravitational physics. This contribution serves as an update on the currently obtained results and their consequences for the test of general relativity in the strong-field regime. A complete and more up-to-date report of the timing results will be presented elsewhere shortly.