Showing papers on "Stellar nucleosynthesis published in 1976"
TL;DR: In this article, the stellar abundances of Li, Be, and B that are relevant to the origin of these light elements and to details of stellar structure are discussed. But the authors focus on the stellar abundance of Li and Be.
Abstract: The present review is concerned with the stellar abundances of Li, Be, and B that are relevant to the origin of these light elements and to details of stellar structure. It is proposed that the best values for the cosmic abundances of these elements can be derived from abundance determinations in stellar atmospheres. The observed abundances are taken to indicate origins in spallation reactions involving galactic cosmic rays, with additional Li-7 probably produced during the big bang. Evidence is presented showing that the Li abundance with which stars are born is depleted during pre-main-sequence evolution, that atoms of the light elements are transported to regions within a star where they are destroyed by (p, alpha) reactions, and that many normal stars have large deficiencies of Li and Be. Overabundances and dilutions of the three elements in Ap stars, supergiants, and giants are discussed along with mechanisms that could account for both super-Li-rich stars and the great range of Li abundances in C and S stars
43 citations
TL;DR: In this article, the authors derived accurate relative abundances of elements in very metal-poor stars of high space motion from new high-resolution spectra, and their abundance results have several implications for nucleosynthesis in the collapsing gas of the galactic halo.
Abstract: We derive accurate relative abundances of elements in very metal-poor stars of high space motion from new high-resolution spectra. Our abundance results have several implications for nucleosynthesis in the collapsing gas of the galactic halo. We rule out the possibility of synthesis by supermassive objects, or by a single event whose products subsequently were diluted. Our abundance results for the elements through the iron peak support explosive nucleosynthesis with a constant ratio of the products of carbon-, oxygen-, and silicon-burning at all (Fe/H), and with low values of the neutron excess at (Fe/H)=-1.5, consistent with helium burning but not hydrostatic carbon burning as the preceding stage of stellar evolution. The relative abundances of the s-process elements show the predicted aging effect, decreasing in proportion to the iron-peak elements as (Fe/H) decreases. The large values derived for the average number of neutron captures at low (Fe/H) argue against /sup 22/Ne as the source of s-process neutrons. The rapid rise of the proportion of s-process elements to the solar-system value at (Fe/H)=-1.0 implies that objects of greater than 5 M/sub sun/ must have been responsible for s-process element production when values of (Fe/H) were low. (AIP)
14 citations
01 Jan 1976
TL;DR: Several states of 16O near the 15N + p threshold are members of isospin multiplets that contain the four lowest levels of 16N and 16F as mentioned in this paper, which are nearly pure one particle configurations.
Abstract: Reactions initiated by protons on 15N have been the object of intensive study for many years. The continuing interest in these reactions is indicative of their importance in several areas. First, at low energies, the reactions are an important hydrogen burning process in stellar nucleosynthesis. The 15N(p, α)12C reaction is part of the carbon-nitrogen cycle, while the 15N(p, γ)16O reaction allows a loss of catalyst from the cycle. Second, the 16O compound system is one of the more important testing grounds for theories of nuclear structure. Several states of 16O near the 15N + p threshold are members of isospin multiplets that contain the four lowest levels of 16N and 16F. These states are nearly pure one particle — one hole configurations and are isospin mixed with nearby T = O states from the same configurations. Finally, the abundance of experimental data on these reactions and the relatively simple spin structures of the initial and final states affords the opportunity for reasonably simple tests of nuclear reaction theories.