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Results for “explosive nucleosynthesis”

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NASA NTRS1997

COMPTEL upper limits for Al-26 and Fe-60 from M82

Gamma ray lines from radioactive isotopes produced in supernova explosions provide information concerning the nucleosynthesis processes in stars before and during the explosion. Regions with high star formation rate are good candidates for such gamma ray lines. Starburst galaxies are examples of such regions with an explosive formation of massive stars. The emission of the most prominent starburst galaxy M 82 is analyzed. Two methods for the determination of the upper limits of fluxes are used to derive 2sigma upper limits for the fluxes of Al-26 and Fe-60 from Compton Gamma Ray Observatory data. These are found to be above the estimated fluxes originating from a supernova rate of 0.1 per year in M 82. An estimation of the necessary observation time for the detection of these fluxes with the Ge spectrometer onboard the International Gamma Ray Astrophysics Laboratory is given.

Georgii, R.↗
NASA NTRS1980

Nucleosynthesis of neutron-rich heavy nuclei during explosive helium burning in a 15 solar-mass supernova

The production of heavy nuclei during explosive helium burning has been calculated using the Weaver and Woosley self-consistent model of a complete 15 solar-mass star and the n-process code of Blake and Schramm. It was found that the resulting neutron-rich heavy nuclei are not produced in the relative abundances of solar-system r-process material (such as a Pt peak) nor are any actinides produced. Basically insufficient neutrons are available.

Blake, J. B.↗
NASA NTRS1981

Nucleosynthesis of neutron-rich heavy nuclei during explosive helium burning in massive stars

The production of heavy nuclei during explosive helium burning has been calculated using a hydrodynamical model of a 15-solar mass (Type II) supernova and an n-process nuclear reaction network. It is found that the resulting neutron-rich heavy nuclei are not produced in the relative abundances of solar-system r-process material, especially in the vicinity of Pt, nor are any actinides produced. These deficiencies reflect an inadequate supply of neutrons. However, some neutron-rich isotopes, normally associated with the r-process, are produced which may be significant for the production of isotopic anomalies in meteorites.

Blake, J. B.↗
NASA NTRS1981

The elements just beyond iron - Formation during explosive carbon burning

It is pointed out that the details of the synthesis of the elements just beyond iron are unclear. Thus, a reexamination of the role played by neutron-capture reactions during explosive carbon burning is indicated. A description is given of calculations of explosive carbon-burning nucleosynthesis using a complete neutron capture (n-process) computer code with a network extending from Cr through Zr and including not only (n,gamma), (gamma,n) reactions and beta-decay but also (p,n), (n,p), (p,gamma), and (p,alpha) reactions. Initial conditions indicative of the composition of a massive star following core helium burning were selected, and a comparison is made with conditions similar to those used by Howard et al. (1972). It is found that neutron reactions during explosive carbon burning are an important source for the elements just beyond iron.

Wefel, J. P.↗
NASA NTRS1971

The chemical evolution of the galaxy

Galaxy chemical evolution, discussing stellar mass loss, supernova explosions, white dwarf formations, nucleosynthesis, cosmochronology, etc

Cameron, A. G. W.↗
NASA NTRS1976

Radioactivity in the galactic plane

The paper reports the detection of a large concentration of interstellar radioactivity during balloon-altitude measurements of gamma-ray energy spectra in the band between 0.02 and 12.27 MeV from galactic and extragalactic sources. Enhanced counting rates were observed in three directions towards the plane of the Galaxy; a power-law energy spectrum is computed for one of these directions (designated B 10). A large statistical deviation from the power law in a 1.0-FWHM interval centered near 1.16 MeV is discussed, and the existence of a nuclear gamma-ray line at 1.15 MeV in B 10 is postulated. It is suggested that Ca-44, which emits gamma radiation at 1.156 MeV following the decay of radioactive Sc-44, is a likely candidate for this line, noting that Sc-44 arises from Ti-44 according to explosive models of supernova nucleosynthesis. The 1.16-MeV line flux inferred from the present data is shown to equal the predicted flux for a supernova at a distance of approximately 3 kpc and an age not exceeding about 100 years.

Walraven, G. D.↗
NASA NTRS1988

Gamma-ray line emission from SN1987A

The inferred average line flux at about 847 keV in the background-subtracted spectrum of SN1987A from August 1 to October 31, 1987 is about (1.0 + or - 0.25) x 10 to the -3rd photons/sq cm/s at an energy of 843 + or - 5 keV. This feature cannot be explained by any statistical or systematic fluctuations observed in the seven previous years of gamma-ray spectrometer data. There is also evidence for the 1238-keV line from Co-56 decay, with an average flux of about (6 + or - 2) x 10 to the -4th photons/sq cm/s. This observation confirms that Co-56 is present in the supernova ejecta and that nucleosynthesis occurred during the explosion.

Matz, S. M.↗
NASA NTRS1990

A new limit on the time between the nucleosynthesis and the acceleration of cosmic rays in supernova remnants using the Co/Ni ratio

Using new cross section measurements of Ni into Co, data on the Co/Ni ratio in cosmic rays from the HEAO C spacecraft have been reinterpreted in terms of the time between nucleosynthesis and the acceleration of cosmic rays, delta t. The observed Co/Ni ratio is now consistent with interstellar fragmentation only, leading to a small or zero source abundance. In terms of the decay of e-process nucleosynthesis nuclides into Co after a supernova explosion, this permits an estimate of delta t = 4-30,000 yr for the time between nucleosynthesis and the acceleration of cosmic rays if supernovae are the direct progenitors of cosmic rays. These age limits are used in conjunction with models of the expansion of supernova remnants (SNRs), to estimate that cosmic rays are accelerated when the radius of these remnants is between 0.1 and 25 pc.

Webber, W. R.↗
NASA NTRS1977

Iron - Whence it came, where it went

Determinations of the abundances of iron and related elements in the photosphere, chromosphere, and corona of the sun as well as in solar and galactic cosmic rays are reviewed and compared with abundances derived from meteoritic data. Observed solar system abundances are found to be in accord with predictions of nucleosynthesis under either hydrostatic or explosive conditions but cannot yet be used to define these processes uniquely. The distribution of iron among planets and meteorites can probably be adequately modelled by condensation and fragmentation under equilibrium conditions above about 700 K, but below that temperature it is likely that inhibited solid-state diffusion perturbed attainment of equilibrium. Pertinent factors which are presently unknown include the mechanism responsible for metal-silicate fractionation, the grain size achieved by metallic iron in the nebula, and whether iron-bearing silicate formed prior to accretion.

Kerridge, J. F.↗
NASA NTRS1990

The nu-process

As the core of a massive star collapses to form a neutron star, the flux of neutrinos in the overlying shells of heavy elements becomes so great that, despite the small cross section, substantial nuclear transmutation is induced. Neutrinos excite heavy elements and even helium to particle unbound levels. The evaporation of a single neutron or proton, and the back reaction of these nucleons on other species present, significantly alters the outcome of traditional nucleosynthesis calculations leading to a new process: nu-nucleosynthesis. Modifications to traditional hydrostatic and explosive varieties of helium, carbon, neon, oxygen, and silicon burning are considered. The results show that a large number of rare isotopes, including many of the odd-Z nuclei from boron through copper, owe much of their present abundance in nature to this process.

Woosley, S. E.↗
NASA NTRS1995

Nucleosynthesis and the nova outburst

A nova outburst is the consequence of the accretion of hydrogen rich material onto a white dwarf and it can be considered as the largest hydrogen bomb in the Universe. The fuel is supplied by a secondary star in a close binary system while the strong degeneracy of the massive white dwarf acts to contain the gas during the early stages of the explosion. The containment allows the temperature in the nuclear burning region to exceed 10(sup 8)K under all circumstances. As a result a major fraction of CNO nuclei in the envelope are transformed into (beta)(sup +)-unstable nuclei. We discuss the effects of these nuclei on the evolution. Recent observational studies have shown that there are two compositional classes of novae; one which occurs on carbon-oxygen white dwarfs, and a second class that occurs on oxygen-neon-magnesium white dwarfs. In this review we will concentrate on the latter explosions since they produce the most interesting nucleosynthesis. We report both on the results of new observational determinations of nova abundances and, in addition, new hydrodynamic calculations that examine the consequences of the accretion process on 1.0M(sub (circle dot)), 1.25M(sub (circle dot)), and 1.35M(sub (circle dot)) white dwarfs. Our results show that novae can produce (sup 22)Na, (sup 26)Al, and other intermediate mass nuclei in interesting amounts. We will present the results of new calculations, done with updated nuclear reaction rates and opacities, which exhibit quantitative differences with respect to published work.

Starrfield, S.↗
NASA NTRS2020

A Nucleosynthetic Origin for the Southwestern Fe-rich Structure in Kepler's Supernova Remnant

Chandra X-ray observations of Kepler's supernova remnant indicate the existence of a high-speed Fe-rich ejecta structure in the southwestern region. We report strong K-shell emission from Fe-peak elements (Cr, Mn, Fe, Ni), as well as Ca, in this Fe-rich structure, implying that those elements could be produced in the inner area of the exploding white dwarf. We found Ca/Fe, Cr/Fe, Mn/Fe, and Ni/Fe mass ratios of 1.0%–4.1%, 1.0%–4.6%, 1%–11%, and 2%–30%, respectively. In order to constrain the burning regime that could produce this structure, we compared these observed mass ratios with those in 18 one-dimensional Type Ia nucleosynthesis models (including both near-M Ch and sub-M Ch explosion models). The observed mass ratios agree well with those around the middle layer of incomplete Si burning in Type Ia nucleosynthesis models with a peak temperature of ~(5.0–5.3) × 10(exp 9) K and a high metallicity, Z > 0.0225. Based on our results, we infer the necessity for some mechanism to produce protruding Fe-rich clumps dominated by incomplete Si-burning products during the explosion. We also discuss the future perspectives of X-ray observations of Fe-rich structures in other Type Ia supernova remnants.

Toshiki Sato↗
NASA NTRS1978

The mean mass of the abundant cosmic-ray nuclei from boron to silicon at 1.2 GeV per atomic mass unit

Results are presented for an investigation of cosmic-ray isotopic composition in which a balloon-borne instrument was used to perform an isotopic analysis of the abundant elements from B through Si in the energy range from 1.0 to 1.6 GeV/amu. The technique employed, which depends on the effect of earth's magnetic field on incoming cosmic rays, and reduction of the observational data are described in detail. Mean masses of the elements B, C, N, O, Ne, Mg, and Si are extracted from normalized Cerenkov spectra and evaluated in terms of the 'leaky box' model of galactic propagation and confinement. The implications of the results for cosmic-ray sources are shown to be consistent with the nucleosynthesis of certain isotopes in the cosmic rays in explosive carbon burning under the conditions of peak temperature, density, and neutronization expected in an explosion of a massive highly evolved star. The possibility of alternate interpretations is noted.

Dwyer, R.↗
NASA NTRS1971

Cosmic rays from supernovae and comments on the Vela X pre-supernova

A possible history of the production of elements in the galaxy is presented, based on assumptions about the end points of stellar evolution and of the general evolution of the galaxy. A wide range of quantities involving the relative abundances of nucleosynthesis products observed in the solar system, and various galactic quantities such as the current rate of supernova production and the present gas content of the galaxy, were considered. These assumptions were utilized in a computer program in which the gas content of the galaxy is gradually turned into stars. The stars are continually enriched in the products of nucleosynthesis as they approach the ends of their evolutionary lifetimes. It is suggested that supernova explosions are associated with the mass range of about 4-8 solar masses. Possible theories on the type of stellar explosive event represented by the Vela supernova are discussed.

Cameron, A. G. W.↗
NASA NTRS1977

UH cosmic rays: Possible origin in massive stars

The origin of the Z greater than 28, ultraheavy, cosmic rays in supernova explosions of massive stars is considered. For Z greater than 70, the UH data is dominated by an r-process source distribution, but for the elements just beyond iron, 29 or = Z less than 36, the data cannot be explained by any single process of nucleosynthesis. This problem is solved naturally in a massive star model by secondary neutron capture reactions occuring during core helium burning and during explosive carbon burning. Interstellar propagation calculations were performed with these episodes of synthesis as source distributions, and the results offer an explanation for the current UH cosmic-ray data. The heavy element synthesis during explosive carbon burning is reexamined using more realistic initial conditions given by the post-helium-burning configuration of the star. Effects of preferential acceleration are considered, and experimental tests are discussed.

Wefel, J. P.↗
NASA NTRS2018

Constraints on the chemical enrichment history of the Perseus Cluster of galaxies from high-resolution X-ray spectroscopy

High-resolution spectroscopy of the core of the Perseus Cluster of galaxies, using the Hitomi satellite above 2 keV and the XMM–Newton Reflection Grating Spectrometer at lower energies, provides reliable constraints on the abundances of O, Ne, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, and Ni. Accounting for all known systematic uncertainties, the Ar/Fe, Ca/Fe, and Ni/Fe ratios are determined with a remarkable precision of less than 10 per cent, while the constraints on Si/Fe, S/Fe, and Cr/Fe are at the 15 per cent level, and Mn/Fe is measured with a 20 percent uncertainty. The average biases in determining the chemical composition using archival CCD spectra from XMM–Newton and Suzaku typically range from 15 to 40 per cent. A simple model in which the enrichment pattern in the Perseus Cluster core and the protosolar nebula are identical gives a surprisingly good description of the high-resolution X-ray spectroscopy results, with X^2=10.7 for 10 degrees of freedom. However, this pattern is challenging to reproduce with linear combinations of existing supernova nucleosynthesis calculations, particularly given the precise measurements of intermediateα-elements enabled by Hitomi. We discuss in detail the degeneracies between various supernova progenitor models and explosion mechanisms, and the remaining uncertainties in these theoretical models. We suggest that including neutrino physics in the core-collapse supernova yield calculations may improve the agreement with the observed pattern ofα-elements in the Perseus Cluster core. Our results provide a complementary benchmark for testing future nucleosynthesis calculations required to understand the origin of chemical elements.

A Simionescu↗
NASA NTRS1997

Gamma-line emission from radioactivities produced in supernovae

The major targets for the gamma ray spectroscopy of supernovae are reviewed. The principle benefit of such observations is the insight provided into the mechanisms of supernova explosions, the distribution and nature of star forming regions in our Galaxy, and the history of the nucleosynthesis of our Galaxy. The emphasis is on two short lived species, Co-56 and Ti-44 which may be seen in individual events and two longer lived species, Al-26 and Fe-60, which can be seen as the cumulative production of many supernovae.

Woosley, S. E.↗
NASA NTRS1978

UH cosmic rays - Possible origin in massive stars

The origin of the Z greater than 28, ultraheavy (UH) cosmic rays in supernova explosions of massive stars, at least about 10 solar masses, is considered. For Z greater than 70, the UH data are dominated by an r-process source distribution, but for the elements just beyond iron, Z from 29 to 36, the data cannot be explained by any single process of nucleosynthesis. This problem is solved naturally in a massive-star model by secondary neutron-capture reactions occurring during core helium burning (a limited s-process) and during explosive carbon burning. Interstellar-propagation calculations have been performed with these episodes of synthesis as source distributions, and the results offer an explanation for the current UH cosmic-ray data. Further, the heavy-element synthesis during explosive carbon burning is re-examined by using more realistic initial conditions given by the post-helium-burning configuration of the star. These results are compared with earlier work and the UH cosmic-ray data. Some effects of preferential acceleration, based upon ionization potential, are considered, and experimental tests for this model are discussed.

Wefel, J. P.↗