[en] The thermonuclear evolution of a 1.41 M solar mass neutron star, with a radius of 14.3 km, accreting various mixtures of hydrogen, helium, and heavy elements at rates of 10^-11 to 10^-10 M solar mass/yr is examined, in conjunction with S.E. Woosley and T.A. Weaver, using a one-dimensional numerical model. We have ignored any effects due to general relativity or magnetic fields. Two cases shall be discussed. In both models, the accretion rate is such that the hydrogen shell burns to helium in steady state, with the hydrogen burning stabilized by the β-limited CNO cycle. A thick helium shell is produced, which is eventually ignited under extremely degenerate conditions, producing a thermonuclear runaway

[en] The nuclear energy generation and nucleosynthesis that occur in hydrogen-rich compositions at temperatures substantially greater than 10⁸ K are examined in detail. At these high temperatures, a new kind of nucleosynthetic process (the rp-process) involving the rapid capture of protons on seed nuclei (or on the products of helium burning in a situation with zero initial metallicity) can lead to the production of heavy elements up to and beyond the iron group with an accompanying energy generation rate greatly modified from that of the β-limited CNO cycle customarily employed in such calculations. New nuclear reaction rates of interest are tabulated, and reaction network calculations are presented to illustrate the application of this process to exploding supermassive stars, accreting neutron stars, novae, and certain chaotic cosmologies. Implications for γ-line astronomy and x-ray burst models are discussed. To further explore the importance of thermonuclear instabilities for accreting neutron stars, the evolution of a 1.41 sub solar neutron star accreting both solar and metal-deficient mixtures of hydrogen, helium, and heavy elements at rates ranging from about 10^-11 to 10^-10 sub solar per year is examined using a one-dimensional numerical model. The metal deficient compositions may result either from placement of the neutron star in a binary system with a Population II Red Giant or from gravitational settling of heavy ions in the accreted material

[en] The importance of p(e^-nu)n and of (p,γ) reactions on ⁵⁶Ni during a thermonuclear runaway on a neutron star surface is pointed out. A fast 16-isotope approximate nuclear reaction network is developed that is suitable for use in hydrodynamic calculations of such events

[en] The thermonuclear evolution of a 1.41 M sub solar neutron star accreting both solar and metal-deficient mixtures of hydrogen, helium, and heavy elements at rates ranging from about 10^-11 to 10^-10 M sub solar per year is examined using a one-dimensional numerical model. The metal deficient compositions may result either from placement of the neutron star in a binary system with a Population II red giant or from gravitational settling of heavy ions in the accreted material. For such accretion rates and metallicities, hydrogen burning, mediated by the β-limited CNO cycle, is stable and leads to the accumulation of a thick helium layer with mass 10²³ to 10²⁵ g and temperature 0.7 less than or equal to T₈ less than or equal to 1.2. Helium ignition occurs under extremely degenerate circumstances and is catastrophically violent. In the lower t helium shells this runaway is propagated as a convective deflagration, for the thicker layers a detonation front is set up which steepens into a strong relativistic shock wave in the neutron star envelope. In all models greatly super-Eddington luminosities in the outer layers of the neutron star lead to a sustained epoch of radiatively driven mass loss. Observationally, such models may correspond to rapid x-ray transients. The hopeless prospect for constructing a one-dimensional model for γ-ray bursts without magnetic field confinement is discussed and uncertainties pointed out in the strong screening correction for helium burning reaction

[en] The thermonuclear evolution of a 1.41 Msub(sun) neutron star, with a radius of 14.3 km, accreting various mixtures of hydrogen, helium, and heavy elements at rates of 10^-₁₁ to 10^-₁₀ Msub(sun)/yr is examined, in conjunction with S.E. Woosley and T.A. Weaver, using a one-dimensional numerical model. We have ignored any effects due to general relativity or magnetic fields. Two cases shall be discussed. In both models, the accretion rate is such that the hydrogen shell burns to helium in steady state, with the hydrogen burning stabilized by the ν-limited CNO cycle. A thick helium shell is produced, which is eventually ignited under extremely degenerate conditions, producing a thermonuclear runaway. (orig.)

[en] The best available published collision strengths for excitation of permitted and semiforbidden emission lines of abundant ions observed or expected in quasars have been collected and averaged over Maxwellian velocity distributions. For a few ions for which calculations are not available, extrapolation along isoelectronic sequences or in principal quantum number n was used to estimate values. These collision strengths were used to correct differentially published photoionization models of quasars, and the corrected models compared with published observational data

[en] The importance of p(e^-ν)n and of (p,γ) reactions on ⁵⁶Ni during a thermonuclear runaway on a neturon star surface is pointed out. A fast 16-isotope approximate nuclear reaction network is developed that is suitable for use in hydrodynamic calculations of such events

[en] The importance of p(e^-ν)n and of (p,γ) reactions on ⁵⁶Ni during a thermonuclear runaway on a neturon star surface is pointed out. A fast 16-isotope approximate nuclear reaction network is developed that is suitable for use in hydrodynamic calculations of such events

[en] The nuclear energy generation and nucleosynthesis that occur in hydrogen-rich compositions at temperatures substantially greater than 10⁸ K are examined in detail. At these high temperatures, a new kind of nucleosynthetic process (the ''rp-process'') involving the rapid capture of protons on seed nuclei (or on the products of helium burning in a situation with zero initial metallicity) can lead to the production of heavy elements up to and beyond the iron group with an accompanying energy generation rate greatly modified from that of the β-limited CNO cycle customarily employed in such calculations. New nuclear reaction rates of interest are tabulated, and reaction network calculations are presented to illustrate the application of this process to exploding supermassive stars, accreting neutron star, novae, and certain chaotic cosmologies. Implications for γ-line astronomy and X-ray burst models are discussed

[en] The production of ν-ray bursts by thermonuclear explosions on strongly magnetized nuetron stars is examined. For a neutron star with a magnetic field strength of several times 10₁₂ gauss, accretion at approx.10^-₁₃ M_sun yr^-₁ is focused onto kilometer sized regions. The accreted material is confined above the surface by the magnetic field and by a combination of magnetic and crustal stresses below the surface. Stable hydrogen burning leads to a critical helium mass that, depending upon model parameters, explodes either by convective deflagration or detonation, liberating 10₃₈--10₄₀ ergs km^-₂ of thermonuclear energy. Multibillion degree plasma pushed above the surface by the explosion has ν>1 and therefore expands and stresses the magnetic field. Hard emission comes both from the magnetically confined photosphere and from relativistic electrons accelerated by magnetic field recombination. The hard ν-ray outburst of several seconds is followed by an enduring, softer emission of X-rays, lasting from several minutes to an hour, as the subsurface ashes of the thermonuclear explosion cool. Gamma-ray bursters, at a typical distance of several hundred parsecs, should recur on a time scale of months (low energy) to centuries (high energy). Special attention is given to the spectracular event of 1979 March 5