An Approximation for the rp-Process

Abstract

Hot (explosive) hydrogen burning or the Rapid Proton Capture Process (rp-process) occurs in a number of astrophysical environments. Novae and X-ray bursts are the most prominent ones, but accretion disks around black holes and other sites are candidates as well. The expensive and often multidimensional hydro calculations for such events require an accurate prediction of the thermonuclear energy generation, while avoiding full nucleosynthesis network calculations. In the present investigation we present an approximation scheme applicable in a temperature range which covers the whole range of all presently known astrophysical sites. It is based on the concept of slowly varying hydrogen and helium abundances and assumes a kind of local steady flow by requiring that all reactions entering and leaving a nucleus add up to a zero flux. This scheme can adapt itself automatically and covers situations at low temperatures, characterized by a steady flow of reactions, as well as high temperature regimes where a $(p,\gamma )-(\gamma ,p)$-equilibrium is established. In addition to a gain of a factor of 15 in computational speed over a full network calculation, and an energy generation accurate to more than 15 %, this scheme also allows to predict correctly individual isotopic abundances. Thus, it delivers all features of a full network at a highly reduced cost and can easily be implemented in hydro calculations.

18 pages, LaTeX using astrobib and aas2pp4, includes PostScript figures; Astrophysical Journal, in press. PostScript source also available at http://quasar.physik.unibas.ch/preps.html

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• Deformations of Accreting Neutron Star Crusts and Gravitational Wave Emission
• Constraining the astrophysical origin of the p-nuclei through nuclear physics and meteoritic data
• Periodic Thermonuclear X-ray Bursts from GS 1826-24 and the Fuel Composition as a Function of Accretion Rate
• The nuclear reaction waiting points, Mg22, Si26, S30, and Ar34, and bolometrically double peaked type I X-ray bursts
• Nuclear Physics of the Outer Layers of Accreting Neutron Stars
• Thermonuclear Kinetics in Astrophysics
• Element Synthesis in Stars
• Nuclear Structure Studies at ISOLDE and their Impact on the Astrophysical r-Process