[en] High temperature (T equal or greater than 10⁸⁰K) CNO cycle burning is studied. An overabundance of both ¹⁷O and ¹⁸O after times of approximately 10² seconds are found. For temperatures of 150 and 200 million degrees it is found that the ¹⁸O abundance is much larger than the ¹⁷O abundance after burning times of about 10³ seconds. Known uncertainties in the nuclear reaction rates do not alter the conclusions. The effects of mixing various amounts of hydrogen-rich material into the intershell convection region of red giants undergoing helium shell flashes were examined. It was found that significant amounts of ¹⁴C can be produced via the ¹⁴N(n,p)¹⁴C reaction. If substantial portions of this intershell region are mixed out into the envelopes of red giants then ¹⁴C may be detectable in evolved stars such as IRC 10216. A neutron number density in the intershell region of approximately 10¹⁵ -- 10¹⁷ cm^-3 and a flux of approximately 10²³ -- 10²⁵ cm^-3 sec^-1 is found. This neutron flux is many orders of magnitude above the flux required for the classical s-process and thus an intermediate neutron process (i-process) may operate in evolved red giants. The neutrons are principally produced by the ¹³C(α,n)¹⁶O reaction. In all cases studied one finds substantial enhancements of ¹⁷O. These mixing models offer a plausible explanation of the observations of enhanced ¹⁷O in the carbon star IRC 10216. For certain physical conditions one finds significant enhancements of ¹⁸O and ¹⁵N in the intershell region

[en] This paper discusses several recent advances toward a deeper understanding of the still unknown astrophysical site for rapid (r-process) neutron capture nucleosynthesis. The physical constraints on the r-process from the input nuclear data are highlighted and the particular importance of the recent measurements of beta-decay lifetimes along the r-process path is discussed. Astronomical observations of s- and r-process elemental abundances on metal poor halo stars are also discussed, in the context of models for the galactic chemical evolution of heavy-element abundances, as a constraint on the nature of the r-process. On the basis of these constraints it is suggested that the most likely source for the r-process may be from the ejection of core material from low-mass type II supernovae. 27 refs., 1 fig

[en] Neutron-capture elements in low metallicity Galactic halo stars vary widely both in overall contents and detailed abundance patterns. This review discusses recent observational results of the n-capture elements, discussing the implications for early Galactic nucleosynthesis of: (a) the star-to-star 'bulk' variations in the n-capture/Fe abundance ratios; (b) the distinct signature of rapid n-capture synthesis events in many (most?) of the lowest metallicity stars; (c) the existence of metal-poor stars heavily enriched in the products of slow n-capture synthesis reactions; and (d) the now-routine detection of radioactive thorium (and even uranium in one and possibly two cases) in the spectra of metal-poor stars

[en] We have examined the results of shock heating of the helium zone in stars undergoing supernova explosions under a wide variety of temperatures and densities. We find that for peak temperatures near 4 x 10⁸ K and peak densities near 10⁴ g cm^-3 the solar system r-process abundance curve can be reproduced. These conditions correspond to shock wave velocities of approximately 4000 km s^-1 in the helium zone of an evolved star. The neutrons to drive the r-process are produced by ¹³C(α, n)¹⁶O reactions. To produce a sufficient flux of neutrons over several seconds requires approximately 2% ¹³C by mass in the helium zone, and thus depends upon some type of mixing between the hydrogen-rich envelope and the helium zone prior to the supernova. We find that neither ²²Ne nor ¹⁸O can provide a sufficient neutron flux in this type of environment. Our calculated fit to the solar system r-process curve is improved when the beta-decay rates of the heavy nuclei are increased by a factor of 5--10 over the rates using the gross theory, compatible with the recent results obtained by Klapdor et al. For reasonable mass ranges of supernova progenitors, a maximum of only 2.2 x 10^-5 M_sun of r-process elements must be ejected per supernova to satisfy galactic nucleosynthesis requirements

[en] The constraints on the universal energy density and cosmological constant from cosmochronological ages and the Hubble age are reviewed. Observational evidence for the galactic chemical evolution of the heavy-element chronometers is described in the context of numerical models. The viability of the recently discovered Th/Nd stellar chronometer is discussed, along with the suggestion that high r-process abundances in metal-poor stars may have resulted from a primordial r-process, as may be required by some inhomogeneous cosmologies

[en] Detailed calculations have been performed to understand more about the nuclear aspects of the r-process and to identify the astrophysical site or sites that produce the r-process nuclei. Some of the nuclear aspects to be considered in these dynamical r-process calculations include neutron-capture cross sections, beta-decay rates, beta-delayed neutron emission, and fission. These calculations can make predictions for nuclear chronometers and the age of the Galaxy. Results of several theoretical r-process calculations, made under very different initial conditions, are also compared to spectroscopic observations of heavy elements in very old stars. This comparison may provide a means of determining the types and extent of nuclear (both r- and s-) processing that occurred early in the history of the Galaxy

[en] The VLA has been used at 20 cm to detect a 0.19 mJy point source at the site of the extraordinary supernova 1961v in NGC 1058. At the distance of NGC 1058, the absolute monochromatic luminosity of the source is comparable to that of Cas A. 20 references

[en] The production of r-process nuclei as a consequence of shock heating of the helium shells in supernovae is examined. The assumption of an initial (seed) distribution which is enriched in heavy s-process elements relative to solar system matter is found to allow production of r-process abundance features compatible with observations. Such an enrichment is consistent, for example, with the high Ba/Sr ratios characteristic of barium stars. This may result from the mixing of hydrogen-rich matter into the helium shells during earlier phases of stellar evolution. With such enrichements, the production of r-process nuclei in solar proportions in the helium shells of supernovae (the helium driven r-process) becomes possible

[en] High-temperature (Tgreater than or equal to10⁸ K) CNO cycle burning is studied. An overabundance of both ¹⁷O and ¹⁸O is found after times of approximately 10² seconds. For temperatures of 150 and 200 million degrees the ¹⁸O abundance is much larger than the ¹⁷O abundance after burning times of about 10³ seconds. Known uncertainties in the nuclear reaction rates do not alter the conclusions

[en] Radio observations of the Sc galaxy NGC 1058 at 20 cm and 6 cm reveal two radio sources. One of the sources is coincident with supernova 1961V and has a spectral index of -0.4 + or - 0.3. This is the second (and probably the third) detection of radio emission from a supernova decades after optical maximum. The absolute luminosity of SN 1961V at 20 cm is comparable to Cas A. A second source, about 2.3 arcsec to the west, has a spectral index of -0.3 + or - 0.3 and is likely to be the remnant of a supernova that was not optically detected. Optical images of NGC 1058 show two faint H II regions associated with the radio sources. Filter photometry in several bands indicates that these two H II regions are normal with respect to the many optically brighter, albeit radio-quiet, H II regions in NGC 1058. 33 references