arXiv subjects

Brad M. S. Hansen

Publications and source records attributed to Brad M. S. Hansen.

57 records · Page 4Linked to original sources

arXiv1997

Stellar Forensics I: Cooling Curves

The presence of low mass, degenerate secondaries in millisecond pulsar binaries offers the opportunity to determine an age for the binary system independent of the rotational properties of the pulsar. To this end, we present here a detailed calculation of the evolution of a grid of low mass ($<0.5 M_{\odot}$) helium core white dwarfs. We investigate the effects of different Hydrogen layer masses and provide results for well-known optical band-passes. We supplement the OPAL opacity calculations with our own calculations for low effective temperatures ($ T_{eff} < 6000 K$) and also provide fitting formulae for the gravity as a function of mass and effective temperature. In paper II we shall apply these results to individual cases.

astro-ph↗

arXiv1997

Stellar Forensics II: Millisecond Pulsar Binaries

We use the grid of models described in paper~I to analyse those millisecond pulsar binaries whose secondaries have been studied optically. In particular, we find cooling ages for these binary systems that range from $< 1 \rm Gyr$ to $\sim \rm 15 Gyr$. Comparison of cooling ages and characteristic spin down ages allows us to constrain the initial spin periods and spin-up histories for individual systems, showing that at least some millisecond pulsars had sub-Eddington accretion rates and long magnetic field decay times.

astro-ph↗

arXiv1997

The Pulsar Kick Velocity Distribution

We analyse the sample of pulsar proper motions, taking detailed account of the selection effects of the original surveys. We treat censored data using survival statistics. From a comparison of our results with Monte Carlo simulations, we find that the mean birth speed of a pulsar is 250-300 km/s, rather than the 450 km/s foundby Lyne & Lorimer (1994). The resultant distribution is consistent with a maxwellian with dispersion $ σ_v = 190 km/s$. Despite the large birth velocities, we find that the pulsars with long characteristic ages show the asymmetric drift, indicating that they are dynamically old. These pulsars may result from the low velocity tail of the younger population, although modified by their origin in binaries and by evolution in the galactic potential.

astro-ph↗