Statistics
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt.........5h&link_type=abstract
Thesis (PH.D.)--CALIFORNIA INSTITUTE OF TECHNOLOGY, 1996.Source: Dissertation Abstracts International, Volume: 57-05, Section: B
Statistics
11
White Dwarf, Supernovas
Scientific paper
We investigate the cooling of low mass white dwarfs with helium cores. We construct a detailed numerical model using the most modern input physics, including our own calculations of low temperature hydrogen opacities. We use our models to constrain the ages of binary millisecond pulsars from the optical observations of their white dwarf companions. We use this to place limits on the initial spin periods, magnetic field decay times and accretion histories of the millisecond pulsars. Our models can also be used along with observations of spectroscopic gravities and radial velocities to place interesting constraints on the neutron star equation of state. We provide grids of temperature and luminosity as a function of age for various white dwarf masses and surface compositions to facilitate future analyses. We have investigated the effect of the pulsar wind on the atmospheric composition of binary companions. The spallation of atmospheric helium to hydrogen increases the cooling age of the white dwarf. We find that all white dwarf companions in binaries with orbital period < 300 days should cool as DA (hydrogen surface layer) white dwarfs, irrespective of their original hydrogen content. We investigate the effect of various wind compositions and note that, if almost all the hydrogen on the surface of a pulsar companion is the result of spallation of an ionic wind, then the D/H ratio is large. We investigate the processes by which planets might form around a millisecond pulsar such as PSR B1257 + 12. We study the evolution of accretion disks of different mass, angular momentum and composition, corresponding to various proposed formation scenarios. We find that most formation scenarios require a high efficiency of conversion of metal-rich material into planets if they are to produce the observed parameters of the 1257 + 12 planetary system. We have studied the distribution of pulsar proper motions in the light of the recent analysis of Lyne & Lorimer (1994). Using a simulation of the selection effects of the various surveys, and treating the censored data using survival statistics, we arrive at an estimate of the characteristic pulsar birth velocity ~300 km.s ^{-1}, 2/3 that of Lyne & Lorimer. We also show that the older pulsar population shows the effects of the asymmetric drift, indicating that it must be dynamically old.
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