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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
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NASA NTRS1981

The carbon abundance in two h 2 regions of the small Megallanic Cloud

Observations of the ultraviolet spectra of two locations in the H II region NGC 346 and of the entire H II region IC 1644 in the Small Magellanic Cloud (SMC) were made using the International Ultraviolet Explorer (IUE) satellite. The abundance of carbon in the nebulae was derived using theoretical model analysis combined with ground-based spectrophotometry of other emission lines. The abundance of C relative to H in the SMC was found to be lower by -0.9 dex compared with the Sun and lower by -0.8 dex compared with the Orion Nebula. This C deficiency is similar to that of O, Ne, S, and Ar in the SMC, but not as great as found for N. The sites and history of C nucleosynthesis in galaxies is similar to that of O, Ne, S, and Ar, in contrast to that of N, which appears to be more complex, perhaps because of a mixture of secondary primary sources or a significant contribution from intermediate-mass long-lived stars.

Dufour, R. J.↗
NASA NTRS1981

Observations of interstellar zinc

The International Ultraviolet Explorer observations of interstellar zinc toward 10 stars are examined. It is found that zinc is at most only slightly depleted in the interstellar medium; its abundance may serve as a tracer of the true metallicity in the gas. The local interstellar medium has abundances that apparently are homogeneous to within a factor of two, when integrated over paths of about 500 pc, and this result is important for understanding the history of nucleosynthesis in the solar neighborhood. The intrinsic errors in detecting weak interstellar lines are analyzed and suggestions are made as to how this error limit may be lowered to 5 mA per target observation.

Jura, M.↗
NASA NTRS1980

Endemic isotopic anomalies in titanium

Abundances of the titanium isotopes were determined using a new high-precision technique that shows terrestrial, lunar, and bulk meteorite samples to be indistinguishable. Ca-Al-Ti-rich inclusions in the Allende meteorite are found to contain Ti of widely varying isotopic composition reflecting the presence of at least three nucleosynthetic components. The anomalies in Ti appear to be relatively widespread and, when correlated with Ca data, provide a clue to nucleosynthesis in the neighborhood of the iron peak and to the late-stage nucleosynthetic processes which immediately preceded formation of the solar nebula.

Niederer, F. R.↗
NASA NTRS1980

Neutrinos and the age of the universe

The age of the universe should be calculable by independent methods with similar results. Previous calculations using nucleochronometers, globular clusters and dynamical measurements coupled with Friedmann models and nucleosynthesis constraints have given different values of the age. A consistent age is reported, whose implications for the constituent mass density are very interesting and are affected by the existence of a third neutrino flavor, and by allowing the possibility that neutrinos may have a non-zero rest mass.

Symbalisty, E. M. D.↗
NASA NTRS1981

Isotopic anomalies in the galactic cosmic-ray source

Observations of the isotopic compositions of oxygen, neon and magnesium nuclei in galactic cosmic rays are presented and discussed in terms of nucleosynthesis at the galactic cosmic ray source. The observations, made with a charged-particle telescope carried aboard ISEE-3, show enhancements in the Ne-22/Ne-20, Mg-25/Mg-24 and Mg-26/Mg-24 ratios with respect to solar system abundances by factors of 4.1, 1.6 and 1.6, respectively. The data thus demonstrate that the galactic cosmic ray source is compositionally distinct from the solar system, and also rule out the models of Woolsey and Weaver (in press) for the synthesis of excess Ne-22 and a model of normal star formation, evolution and mass loss in a region enriched in metals.

Wiedenbeck, M. E.↗
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 NTRS1981

Interpretations and implications of gamma-ray lines from solar flares, the galactic centre and gamma-ray transients

Gamma-ray line emission from the Sun results from the nuclear interactions of energetic protons and nuclei with the solar atmosphere. These interactions produce gamma-ray lines from neutron capture, positron annihilation, and nuclear deexcitation. Observation of such gamma-rays can provide unique information on high energy processes at the Sun. Details of solar gamma-ray spectroscopy are discussed along with the galactic center 0.511 MeV line. The richness of astronomy at 0.511 MeV is indicated by the great variety of astrophysical positron production mechanisms and by the many astrophysical sites where such mechanisms could operate. Attention is also given to lines from gamma-ray transients, and the prospects for gamma-ray line detections, taking into account gamma-ray lines from processes of nucleosynthesis and lines from low-energy cosmic ray interactions.

Ramaty, R.↗
NASA NTRS1981

Future prospects for gamma-ray astronomy

As gamma-ray astronomy moves from the discovery to the exploratory phase, the promise of gamma-ray astrophysics noted by theorists in the late 1940s and 1950s is beginning to be realized. In the future, satellites should carry instruments that will have over an order of magnitude greater sensitivity than those flown thus far, and, for at least some portions of the gamma-ray energy range, these detectors will also have substantially improved energy and angular resolution. The information to be obtained from these experiments should greatly enhance our knowledge of several astrophysical phenomena including the very energetic and nuclear processes associated with compact objects, astrophysical nucleosynthesis, solar particle acceleration, the chemical composition of the planets and other bodies of the solar system, the structure of our galaxy, the origin and dynamic pressure effects of the cosmic rays, high energy particles and energetic processes in other galaxies especially active ones, and the degree of matter-antimatter symmetry of the universe. The gamma-ray results of the forthcoming programs such as Gamma-I, the Gamma Ray Observatory, the gamma-ray burst network, Solar Polar, and very high energy gamma-ray telescopes on the ground will almost certainly provide justification for more sophisticated telescopes. These advanced instruments might be placed on the Space Platform currently under study by N.A.S.A.

Fichtel, C.↗
NASA NTRS1981

Isotopically anomalous xenon in meteorites - A new clue to its origin

The CCF xenon component in primitive meteorites, which has been attributed either to fission of a superheavy element or to nucleosynthesis in a supernova, does not show the large enrichment in Xe-129 (from decay of 16 Myr I-129) expected for supernova ejecta. Although this problem can be circumvented by ad hoc assumptions, a fission origin of CCFXe seems more likely.

Lewis, R. S.↗
NASA NTRS1981

Cosmic-ray abundances of elements with atomic number 26 less than or equal to 40 measured on HEAO 3

Individual elements in the cosmic radiation of even atomic number (Z) in the interval 26-40 have been resolved and their relative abundances measured. The results are inconsistent with a cosmic-ray source whose composition in this charge interval is dominated by r-process nucleosynthesis. The ratios of cosmic-ray source abundances to solar system abundances in this interval follow the same general correlation with first ionization potential as for the lighter elements, although there are deviations in detail.

Binns, W. R.↗
NASA NTRS1982

Abundance fluctuations in the interstellar medium

The determination of abundances within the interstellar medium is reviewed. It appears that interstellar abundances within 1 kpc of the Sun are uniform to within a factor of two or three, but it is not yet possible to determine whether there are real fluctuations at this level except for deuterium for which the factor of two variations appear to be real. Establishing the level of local fluctuations in the abundances is of considerable importance for understanding the history of nucleosynthesis in the solar neighborhood, the evolution of the interstellar medium and the formation of stars.

Jura, M.↗
NASA NTRS1982

Binary stars: Mass transfer and chemical composition

It is noted that mass exchange (and mass loss) within a binary system should produce observable changes in the surface chemical composition of both the mass losing and mass gaining stars as a stellar interior exposed to nucleosyntheses is uncovered. Three topics relating mass exchange and/or mass loss to nucleosynthesis are sketched: the chemical composition of Algol systems; the accretion disk of a cataclysmic variable fed by mass from a dwarf secondary star; and the hypothesis that classical Ba II giants result from mass transfer from a more evolved companion now present as a white dwarf.

Lambert, D. L.↗
NASA NTRS1981

Discovery of interstellar rubidium

Interstellar rubidium is detected through observations of the resonance line of Rb I at 7800 A towards zeta Oph. The abundance ratio of rubidium to potassium is estimated to be approximately solar, and if rubidium is generally found to have an abundance similar to potassium, it is indicated that the local interstellar medium is well mixed with a wide variety of the products of nucleosynthesis.

Jura, M.↗
NASA NTRS1982

The charge and isotopic composition of Z = 6-14 cosmic ray nuclei at their source

Using data from a cosmic ray charge-isotope telescope flown on balloons, both the charge and isotopic composition are determined of Z = 6-14 cosmic ray nuclei. A low abundance for the elements N and Ne in the cosmic ray source relative to solar cosmic rays is observed. For the isotopes, a cosmic ray source ratio Ne-22/Ne-20 is found that is 3.52 plus or minus 0.67 times the solar ratio, this enhancement being due in part to an enhancement of Ne-22 and in part to an underabundance of Ne-20. Also observed are possible enhancements of the Mg-26/Mg-24 ratio, which is 1.40 plus or minus 0.24 times the solar t ratio, and the C-13/C-12 ratio, which is 2.90 plus or minus 0.93 times the solar ratio. For Ne, the underabundance of this element, coupled with the overabundnace of the isotope Ne-22, is seen as providing an important new clue to the nucleosynthesis processes producing these differences.

Webber, W. R.↗
NASA NTRS1981

Radio observations of molecules in the interstellar gas

Since 1968, radio astronomy has made it possible to identify nearly 50 molecules in the dense concentrations of the interstellar gas now generally termed molecular clouds. Most interstellar molecules are familiar stable compounds. However, one-fifth of the discovered species are ions, radicals, and acetylenic carbon chains so reactive in the laboratory that before being detected in space they had rarely been observed or were entirely unknown. The heavy atom backbone of the known interstellar molecules is a linear chain of C, N, O, or S. Si is found in two diatomic molecules. Rings and branched chains are missing. The most readily observed spectral lines of most interstellar molecules correspond to rotational transitions at millimeter wavelengths. These are generally excited by H2 collisions. A number of rare isotopic species are observed in interstellar molecules. Isotopic ratios differing from those on Earth exist, and can in almost all cases be attributed to stellar nucleosynthesis since the formation of the solar system.

Thaddeus, P.↗
NASA NTRS1980

A first roadmap for kryptology

Studies of the complex variations of the isotopic composition of xenon in the solar system have been christened 'xenology'. In the title of the present investigation, the word 'kryptology' is employed to indicate the primary objective of the reported studies. This objective is related to the prediction of the isotopic composition of krypton which comes from a number of specific locations of a supernova in association with the isotopic compositions of xenon from these locations. Krypton is a logical candidate for testing the stellar theory on geochemical grounds, taking into account also the point of view of nucleosynthesis, because the isotopes of xenon and krypton are formed by the same thermonuclear processes in stars. The data and arguments presented in the investigation show that the treatment by Heymann and Dziczkaniec (1979), although not wrong, is too simplistic, because it has ignored the possibility of holdup and arrest in Xe network.

Heymann, D.↗
NASA NTRS1981

Implications of ultraheavy cosmic-ray source composition derived from observations by the HEAO-3 heavy nuclei experiment

The contribution of r-process and s-process nucleosynthesis to the Cameron (1980) solar system (SS) abundances for Z at least 33 has been derived. In the interval Z equals 34-40 HEAO-3 data extrapolated to the cosmic-ray source (CRS) fit the solar system mix better than r-process. In the interval Z between 26-40 the HEAO-3 results for CRS/SS follow the same general correlation with first ionization potential as for the lighter elements although there are deviations in detail.

Israel, M. H.↗
NASA NTRS1981

Nuclear and particle physics in the early universe

Basic principles and implications of Big Bang cosmology are reviewed, noting the physical evidence of a previous universe temperature of 10,000 K and theoretical arguments such as grand unification decoupling indicating a primal temperature of 10 to the 15th eV. The Planck time of 10 to the -43rd sec after the Big Bang is set as the limit before which gravity was quantized and nothing is known. Gauge theories of elementary particle physics are reviewed for successful predictions of similarity in weak and electromagnetic interactions and quantum chromodynamic predictions for strong interactions. The large number of photons in the universe relative to the baryons is considered and the grand unified theories are cited as showing the existence of baryon nonconservation as an explanation. Further attention is given to quark-hadron phase transition, the decoupling for the weak interaction and relic neutrinos, and Big Bang nucleosynthesis.

Schramm, D. N.↗