[en] 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 hydrocalculations 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 that leads to accuracy of more than 15% for the energy generation in hot hydrogen burning from 10⁸-1.5x10⁹K, 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 low-temperature regimes, characterized by a steady flow of reactions, as well as high-temperature regimes where a (p,γ)-(γ,p)-equilibrium is established, while β⁺-decays or (α,p)-reactions feed the population of the next isotonic line of nuclei. In addition to a gain of a factor of 15 in computational speed over a full-network calculation and energy generation accurate to more than 15% this scheme also allows the correct prediction of individual isotopic abundances. Thus, it delivers all features of a full network at a highly reduced cost and can easily be implemented in hydrocalculations. copyright 1997 The American Astronomical Society

[en] We give an overview of explosive burning and the role which neutron and/or proton separation energies play. We focus then on the rapid neutron capture process (r-process) which encounters unstable nuclei with neutron separation energies in the range 1-4 MeV, and the rapid proton capture process (rp-process), operating close to the proton drip-line. The site of the rp-process is related to hydrogen accreting neutron stars in binary stellar systems. Explosive H-burning produces nuclei as heavy as A=100, powering events observable as X-ray bursts. The r-process abundances witness nuclear structure far from beta-stability as well as the conditions in the appropriate astrophysical environment. But there is a remaining lack in the full understanding of its astrophysical origin, ranging from the high entropy neutrino wind, blown from hot neutron star surfaces after a supernova explosion, to low entropy ''cold decompression'' of neutron star matter ejected in mergers of binary neutron star systems. (author)

[en] The rp-process has been suggested as the dominant nucleosynthesis process in explosive hydrogen burning at high temperature and density conditions. The process is characterized by a sequence of fast proton capture reactions and subsequent β-decays. The reaction path of the rp-process runs along the drip line up to Z∼50. Most of the charged-particle reaction rates for the reaction path are presently based on statistical Hauser-Feshbach calculations. While these rates are supposed to be reliable within a factor of two for conditions of high density in the compound nuclei, discrepancies may occur for nuclei near closed shells or near the proton drip line where the Q-values of proton capture processes are typically very small. It has been argued that the thermonuclear runaway is less sensitive to the reaction rates because of the rapid time-scale of the event. However, since these processes may operate at the same time-scale as fast mixing and convection processes, a change in reaction rates indeed may have a significant impact. In this paper we present two examples, the break-out from the hot CNO cycles, and the thermonuclear runaway in X-ray bursts itself, where changes in reaction rates have a direct impact on time-scale, energy generation and nucleosynthesis predictions for the explosive event. (orig.)