PSR J0045−7319: A Dual-Line Binary Radio Pulsar

Abstract

Binary radio pulsars are superb tools for mapping binary orbitsbecause of the precision of the pulse timing method (e.g., Taylor &Weisberg). To date, all orbital parameters for binary pulsars have beenderived from observations of the pulsar alone. We present the firstobservations of the radial velocity variations due to the binary motionof a companion to a radio pulsar. Our results demonstrate that thecompanion to the Small Magellanic Cloud pulsar J0045-7319 is theB1 V star identified by Kaspi et al. The mass ratio of the systemis 6.3 +/- 1.2, which, for a neutron star mass of 1.4 M��, impliesa mass of 8.8 +/- 1.8 M�� for the companion, consistent with themass expected for a B1 V star. The inclination angle for the binarysystem is therefore 44 deg +/- 5 deg, and the projected rotationalvelocity of the companion is 113 +/- 10 km s-1. The heliocentricradial velocity of the binary system is consistent with that of otherstars and gas in the same region of the Small Magellanic Cloud.