Neutron stars in mass-transferring binaries accrete hydrogen and helium rich matter from their companions. Unstable nuclear burning of this matter results in Type I X-ray bursts every few hours to days. Theoretical models propose three regimes of unstable burning on neutron star surfaces and also define the critical accretion rate above which the neutron star burns fuel stably without bursting. Currently, the theoretical value for this stability boundary is comparable to the Eddington limit whereas the observational limit is estimated to 0.3 m˙Edd. In this dissertation, we examine the boundary between stable and unstable thermonuclear burning at the surface of an accreting neutron star for a range of initial compositions. We compute different steady-state equilibrium models and use them to conduct a linear perturbation analysis. The main results of this analysis are plots of the critical accretion rates as a function of the initial helium mass fraction which were never produced before.

No description available.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, August 2000. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Washington, 1999. / Includes bibliographical references (p. [135]-143).

No description available.

Thesis (Ph.D.) -- University of Western Sydney, 2002. / "Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy, University of Western Sydney" Bibliography.

<p>This thesis describes a new experimental approach that has been designed to determine the alpha-branching ratio of the 4.03-MeV excited state of Ne-19. A precise measurement of this quantity is needed to reduce reaction rate uncertainties in Type I x-ray bursts models. The alpha-branching will be measured by the detection of the beta+ activity of the associated alpha-decay product. This activity method has been modelled using two separate simulations. The first, a Monte Carlo code to simulate the reaction process and energy distributions of the decay products. Secondly, a GEANT4 simulation was created to predict the detector response to the O-15 beta+ activity. Along with the simulations two NaI(Tl) detectors, which were customized to this experiment's geometric constraints, have been tested and their response and resolution have been determined. The results of this work will be used to refine the experimental setup such that the proposed test run and eventual alpha-branching ratio measurement of the 4.03-MeV state will be successful. With the results of the simulations and subsequent yield calculations, it has been found that reasonable statistical significance in the O-15 yield from the 4.03-MeV excited state in Ne-19 can be achieved within 10 days of beamtime.</p> / Master of Science (MSc)