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Nucleosynthesis in O-Ne-Mg Supernovae

Description: We have studied detailed nucleosynthesis in the shocked surface layers of an oxygen-neon-magnesium core collapse supernova with an eye to determining whether the conditions are suitable for r-process nucleosynthesis. We find no such conditions in an unmodified model, but do find overproduction of N=50 nuclei (previously seen in early neutron-rich neutrino winds) in amounts that, if ejected, would pose serious problems for Galactic chemical evolution.
Date: December 18, 2007
Creator: Hoffman, R D; Janka, H & Muller, B
Partner: UNT Libraries Government Documents Department

On the solution to the Polonyi problem with no-scale type supergravity

Description: We study the solution to the Polonyi problem in the framework of no-scale type supergravity. In such a model, Polonyi field can weigh as O(10TeV) and decay just before the big-bang nucleosynthesis. It is shown that in spite of a large entropy production by the decay of the Polonyi field, one can naturally explain the present value of the baryon-to-entropy ratio, {eta}{sub B}/S {approximately} (10{sup {minus}10} {minus} 10{sup {minus}11}) if the Affleck-Dine mechanism for baryogenesis works. It is pointed out, however, that there is another cosmological problem related to the abundance of the lightest superparticles produced by the decay of the Polonyi field.
Date: October 1, 1995
Creator: Moroi, T.
Partner: UNT Libraries Government Documents Department

Atomic and molecular supernovae

Description: Atomic and molecular physics of supernovae is discussed with an emphasis on the importance of detailed treatments of the critical atomic and molecular processes with the best available atomic and molecular data. The observations of molecules in SN 1987A are interpreted through a combination of spectral and chemical modelings, leading to strong constraints on the mixing and nucleosynthesis of the supernova. The non-equilibrium chemistry is used to argue that carbon dust can form in the oxygen-rich clumps where the efficient molecular cooling makes the nucleation of dust grains possible. For Type Ia supernovae, the analyses of their nebular spectra lead to strong constraints on the supernova explosion models.
Date: December 1, 1997
Creator: Liu, W.
Partner: UNT Libraries Government Documents Department

Light and heavy element isotopic compositions of mainstream SiC grains.

Description: Although a variety of types of pre-solar SiC grains have been classified by their C, N, and Si isotopic composition, the majority of such grains are so-called mainstream grains and are believed to have come from asymptotic giant branch stars [1]. We have previously reported the Mo isotopic compositions of presolar SiC grains whose C, N, and Si isotopic compositions were not known [2]. Since most presolar SiC grains fall in the mainstream group, we assumed that these grains were mainstream. The excellent match of the Mo isotopic data with expectations for nucleosynthesis in AGB stars was consistent with this identification. In order to better understand the distribution of isotopic compositions in presolar grains, we have begun to measure heavy element isotopic compositions of presolar SiC grains of known C, N and Si isotopic composition.
Date: February 3, 1999
Creator: Amari, S.; Clayton, R. N.; Davis, A. M.; Lewis, R. S. & Pellin, M. J.
Partner: UNT Libraries Government Documents Department

Collaborative Research: Neutrinos & Nucleosynthesis in Hot Dense Matter

Description: It is now firmly established that neutrinos, which are copiously produced in the hot and dense core of the supernova, play a role in the supernova explosion mechanism and in the synthesis of heavy elements through a phenomena known as r-process nucleosynthesis. They are also detectable in terrestrial neutrino experiments, and serve as a probe of the extreme environment and complex dynamics encountered in the supernova. The major goal of the UW research activity relevant to this project was to calculate the neutrino interaction rates in hot and dense matter of relevance to core collapse supernova. These serve as key input physics in large scale computer simulations of the supernova dynamics and nucleosynthesis being pursued at national laboratories here in the United States and by other groups in Europe and Japan. Our calculations show that neutrino production and scattering rate are altered by the nuclear interactions and that these modifications have important implications for nucleosynthesis and terrestrial neutrino detection. The calculation of neutrino rates in dense matter are difficult because nucleons in the dense matter are strongly coupled. A neutrino interacts with several nucleons and the quantum interference between scattering off different nucleons depends on the nature of correlations between them in dense matter. To describe these correlations we used analytic methods based on mean field theory and hydrodynamics, and computational methods such as Quantum Monte Carlo. We found that due to nuclear effects neutrino production rates at relevant temperatures are enhanced, and that electron neutrinos are more easily absorbed than anti-electron neutrinos in dense matter. The latter, was shown to favor synthesis of heavy neutron-rich elements in the supernova.
Date: September 6, 2013
Creator: Reddy, Sanjay
Partner: UNT Libraries Government Documents Department

GRBs from the First Stars

Description: We present an estimate of the Gamma Ray Bursts which should be expected from metal-free, elusive first generation of stars known as PopulationIII (PopIII). We derive the GRB rate from these stars from the Stellar Formation Rate obtained in several Reionization scenarios available in the literature. In all of the analyzed models we find that GRBs from PopIII are subdominant with respect to the ''standard'' (PopII) ones up to z {approx} 10.
Date: April 16, 2007
Creator: Iocco, Fabio & /Naples U. /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Compulsory Deep Mixing of 3He and CNO Isotopes on the First Giant Branch

Description: We have found a deep-mixing process which occurs during First Giant Branch (FGB) evolution. It begins at the point in evolution where the surface convection zone (SCZ), having previously grown in size, starts to shrink, and it is driven by a local minimum that develops in the mean molecular weight as a result of the burning of {sup 3}He. This mixing can solve two important observational problems. One is why the interstellar medium (ISM) has not been considerably enriched in {sup 3}He since the Big Bang. The other is why products of nucleosynthesis such as {sup 13}C are progressively enriched on the upper FGB, when classical stellar modeling says that no further enrichment should take beyond the First Dredge-Up (FDU) episode, somewhat below the middle of the FGB.
Date: July 26, 2007
Creator: Eggleton, P P; Dearborn, D P & Lattanzio, J
Partner: UNT Libraries Government Documents Department

Compulsory Deep Mixing of 3He and CNO Isotopes in the Envelopes of low-mass Red Giants

Description: Three-dimensional stellar modeling has enabled us to identify a deep-mixing mechanism that must operate in all low mass giants. This mixing process is not optional, and is driven by a molecular weight inversion created by the {sup 3}He({sup 3}He,2p){sup 4}He reaction. In this paper we characterize the behavior of this mixing, and study its impact on the envelope abundances. It not only eliminates the problem of {sup 3}He overproduction, reconciling stellar and big bang nucleosynthesis with observations, but solves the discrepancy between observed and calculated CNO isotope ratios in low mass giants, a problem of more than 3 decades standing. This mixing mechanism operates rapidly once the hydrogen burning shell approaches the material homogenized by the surface convection zone. In agreement with observations, Pop I stars between 0.8 and 2.0 M{sub {circle_dot}} develop {sup 12}C/{sup 13}C ratios of 14.5 {+-} 1.5, while Pop II stars process the carbon to ratios of 4.0 {+-} 0.5. In stars less than 1.25 M{sub {circle_dot}}, this mechanism also destroys 90% to 95% of the {sup 3}He produced on the main sequence.
Date: March 20, 2007
Creator: Eggleton, P P; Dearborn, D P & Lattanzio, J C
Partner: UNT Libraries Government Documents Department

The path to metallicity: Synthesis of CNO elements in standard BBN

Description: We perform a reanalysis of the production of CNO elements in a standard Big Bang Nucleosynthesis scenario. The CNO yields in BBN are suppressed by the low density of the plasma, Coulomb barrier effects and the short time scales involved. Yet, the inclusion of nuclides and reactions traditionally disregarded may lead to an increase relevant enough to affect the pristine Population III stars. After a critical reanalysis and upgrade of the nuclear network our results show no major discrepancies with the ones obtained using a smaller nuclear network. The robustness of the standard predictions--the early generation of star developed in a metal-free environment--is confirmed.
Date: February 1, 2007
Creator: Iocco, Fabio; /Naples U. /INFN, Naples /KIPAC, Menlo Park; Mangano, G.; Miele, G.; Pisanti, O.; /Naples U. /INFN, Naples et al.
Partner: UNT Libraries Government Documents Department

Quark mass variation constraints from Big Bang nucleosynthesis

Description: We study the impact on the primordial abundances of light elements created of a variation of the quark masses at the time of Big Bang nucleosynthesis (BBN). In order to navigate through the particle and nuclear physics required to connect quark masses to binding energies and reaction rates in a model-independent way we use lattice QCD data and an hierarchy of effective field theories. We find that the measured {sup 4}He abundances put a bound of {delta}-1% {approx}< m{sub q}/m{sub 1} {approx}< 0.7%. The effect of quark mass variations on the deuterium abundances can be largely compensated by changes of the baryon-to-photon ratio {eta}. Including the bounds on the variation of {eta} coming from WMAP results and some additional assumptions narrows the range of allowed values of {delta}m{sub q}/m{sub q} somewhat.
Date: December 13, 2010
Creator: Bedaque, P.; Luu, T. & Platter, L.
Partner: UNT Libraries Government Documents Department

MSW without matter

Description: We examine the effects of a scalar field, coupled only to neutrinos, on oscillations among weak interaction current eigenstates. The existence of a real scalar field is manifested as effective masses for the neutrino mass3 eigenstates, the same for F, as for v. Under some conditions, this can lead to a vanishing of {delta}m{sup 2}, giving rise to MSW-like effects. We present an idealized example and show that it may be possible to resolve the apparent discrepancy in spectra required by reprocess nucleosynthesis in the mantles of supernovae and by Solar neutrino solutions.
Date: September 1, 1996
Creator: Goldman, T.; McKellar, B.H.J. & Stephneson, G.J. Jr.
Partner: UNT Libraries Government Documents Department

Studies of modern and ancient solar energetic particles

Description: Modern solar energetic particles (SEPs) have been studied for about 50 years by satellites and ground-based observations. These measurements indicate much about the nature of SEPs but cover too short a period to quantify the probabilities of very large solar particle events. Many SEPs have high enough energies to make nuclides in material in which they interact. Some nuclides measured in lunar samples have been used to extend the record about SEPs back several million years. Some new measurements of modern SEPs during the last solar cycle and new results for nuclides made by SEPs in lunar samples are presented and their implications discussed. Both the modern and ancient records need to be improved, and methods to get a better understanding of solar energetic particles are discussed. The SEP average fluxes from both sets of records are similar, and both sets can be used to show that huge fluxes of SEPs are very rare.
Date: October 1, 1998
Creator: Reedy, R.C.
Partner: UNT Libraries Government Documents Department

New studies of nuclear decay {gamma}-rays from novae

Description: The cause of the nova outburst is a thermonuclear runaway (TNR) in hydrogen rich material transferred by a companion onto a white dwarf. Studies of this phenomenon have shown that the TNR produces large concentrations of the short lived positron unstable isotopes of the CNO nuclei which are transported to the surface by convection so that early in the outburst we expect significant numbers of radioactive decays to occur at the surface. The resulting {gamma}-ray emission may be detectable from nearby novae early in their outbursts. The TNR is also expected to produce substantial amounts of {sup 7}Be and {sup 22}Na. Their decays also yield potentially detectable levels of {gamma}-ray emission for relatively nearby novae. We are also interested in the role played by novae in the production of the {approximately}2M{circle_dot} of {sup 26}Al found in the galaxy. In order to improve our predictions of this phenomenon, we have performed a new set of calculations of TNR`s on ONeMg and CO white dwarfs with an updated nuclear reaction network and opacities.
Date: November 1, 1997
Creator: Starrfield, S.; Truran, J.W. & Wiescher, M.C.
Partner: UNT Libraries Government Documents Department

Observational and theoretical studies of the nova outburst

Description: A nova outburst is one consequence of the accretion of hydrogen rich material onto a white dwarf in a close binary system. The strong electron degeneracy of a massive white dwarf drives the temperatures in the nuclear burning region to values exceeding 108K under all circumstances. As a result, a major fraction of the CNO nuclei in the envelope are transformed into e{sup +}-decay nuclei, which constrains the nuclear energy generation and yields non-solar CNO isotopic abundance ratios. In addition, the observations demonstrate that white dwarf core material is dredged up into the accreted layers and these nuclei are the catalysts for producing peak rates of energy generation that can exceed 10{sup 16} erg gm{sup -1}s{sup -1}. Observations show that there are two compositional classes of novae, one that occurs on a carbon-oxygen white dwarf and the other that occurs on an oxygen-neon-magnesium white dwarf.
Date: April 1, 1998
Creator: Starrfield, S.; Vanlandingham, K. & Schwarz, G.
Partner: UNT Libraries Government Documents Department

Neutron Capture Measurements on Unstable Nuclei at LANSCE

Description: Although neutron capture by stable isotopes has been extensively measured, there are very few measurements on unstable isotopes. The intense neutron flux at the Manual Lujan Jr. Neutron Scattering Center at LANSCE enables us to measure capture on targets with masses of about 1 mg over the energy range from 1 eV to 100 keV. These measurements are important not only for understanding the basic physics, but also for calculations of stellar nucleosynthesis and Science-Based Stockpile Stewardship. Preliminary measurements on {sup 169}Tm and {sup 171}Tm have been made with deuterated benzene detectors. A new detector array at the Lujan center and a new radioactive isotope separator will combine to give Los Alamos a unique capability for making these measurements.
Date: November 4, 1998
Creator: Ullmann, J.; Haight, R.; Wilhelmy, J.; Fowler, M.; Rundberg, R. & Miller, G.
Partner: UNT Libraries Government Documents Department

Simplifying silicon burning: Application of quasi-equilibrium to {alpha} network nucleosynthesis

Description: While the need for accurate calculation of nucleosynthesis and the resulting rate of thermonuclear energy release within hydrodynamic models of stars and supernovae is clear, the computational expense of these nucleosynthesis calculations often force a compromise in accuracy to reduce the computational cost. To redress this trade-off of accuracy for speed, the authors present an improved nuclear network which takes advantage of quasi-equilibrium in order to reduce the number of independent nuclei, and hence the computational cost of nucleosynthesis, without significant reduction in accuracy. In this paper they will discuss the first application of this method, the further reduction in size of the minimal alpha network. The resultant QSE-reduced alpha network is twice as fast as the conventional alpha network it replaces and requires the tracking of half as many abundance variables, while accurately estimating the rate of energy generation. Such reduction in cost is particularly necessary for future generation of multi-dimensional models for supernovae.
Date: December 1, 1997
Creator: Hix, W.R.; Thielemann, F.K.; Khokhlov, A.M. & Wheeler, J.C.
Partner: UNT Libraries Government Documents Department

New developments in the mechanism for core-collapse supernovae

Description: Recent results indicate that the standard type-2 supernova scenario in which the shock wave stagnates but is reenergized by neutrino heating fails to consistently produce supernova explosions having the required characteristics. The authors review the theory of convection and survey some recent calculations indicating the importance of convection operating on millisecond timescales in the protoneutron star. These calculations suggest that such convection is probably generic to the type-2 scenario, that this produces a violet overturn of material below the stalled shock, and that this overturn could lead to significant alterations in the neutrino luminosity and energy. This provides a mechanism that could be effective in reenergizing the stalled shock and producing supernovae explosions having the quantitative characteristics demands by observations. This mechanism implies, in turn, that the convection cannot be adequately described by the 1-dimensional hydrodynamics employed in most simulations. Thus, a full understanding of the supernova mechanism and the resulting heavy element production is likely to require 3-dimensional relativistic hydrodynamics and a comprehensive description of neutrino transport. The prospects for implementing such calculations using a new generation of massively parallel supercomputers and modern scalable algorithms are discussed.
Date: December 1994
Creator: Guidry, M.
Partner: UNT Libraries Government Documents Department

The evolution and explosion of massive Stars II: Explosive hydrodynamics and nucleosynthesis

Description: The nucleosynthetic yield of isotopes lighter than A = 66 (zinc) is determined for a grid of stellar masses and metallicities including stars of 11, 12, 13, 15, 18, 19, 20, 22, 25, 30, 35, and 40 M{sub {circle_dot}} and metallicities Z = 0, 10{sup {minus}4}, 0.01, 0.1, and 1 times solar (a slightly reduced mass grid is employed for non-solar metallicities). Altogether 78 different model supernova explosions are calculated. In each case nucleosynthesis has already been determined for 200 isotopes in each of 600 to 1200 zones of the presupernova star, including the effects of time dependent convection. Here each star is exploded using a piston to give a specified final kinetic energy at infinity (typically 1.2 {times} 10{sup 51} erg), and the explosive modifications to the nucleosynthesis, including the effects of neutrino irradiation, determined. A single value of the critical {sup 12}C({sub {alpha},{gamma}}){sup 16}O reaction rate corresponding to S(300 keV) = 170 keV barns is used in all calculations. The synthesis of each isotope is discussed along with its sensitivity to model parameters. In each case, the final mass of the collapsed remnant is also determined and often found not to correspond to the location of the piston (typically the edge of the iron core), but to a ``mass cut`` farther out. This mass cut is sensitive not only to the explosion energy, but also to the presupernova structure, stellar mass, and the metallicity. Unless the explosion mechanism, for unknown reasons, provides a much larger characteristic energy in more massive stars, it appears likely that stars larger than about 30 M{sub {center_dot}} will experience considerable reimplosion of heavy elements following the initial launch of a successful shock. While such explosions will produce a viable, bright Type II supernova light curve, lacking the radioactive tail, they will have dramatically ...
Date: August 30, 1995
Creator: Woosley, S.E. & Weaver, T.A.
Partner: UNT Libraries Government Documents Department

Nuclear structure and astrophysics with accelerated beams of radioactive ions: A new multidisciplinary research tool

Description: After a brief discussion of the techniques for producing accelerated radioactive ion beams (RIBs), several recent scientific applications are mentioned. Three general nuclear structure topics, which can be addressed using RIBs, are discussed in some detail: possible modifications of the nuclear shell structure near the particle drip lines; various possibilities for decoupling the proton and neutron mass distributions for weakly bound nuclei; and tests of fundamental nuclear symmetries for self-conjugate and nearly self-conjugate nuclei. The use of RIBs to study r- and rp-process nucleosynthesis also is discussed.
Date: December 31, 1995
Creator: Garrett, J.D.
Partner: UNT Libraries Government Documents Department

Inhomogeneous primordial nucleosynthesis and new abundance constraints on {Omega}{sub b}h{sup 2}

Description: We discuss the upper limit to the baryonic contribution to the closure density. We consider effects of new observational and theoretical uncertainties in the primordial light element abundances, and the effects of fluctuation geometry on the inhomogeneous nucleosynthesis yields. We also consider implications of the possible detection of a high D/H abundance in a Lyman-{alpha} absorption cloud at high redshift and the implied chemical evolution effects of a high deuterium abundance. We show that there exists a region of the parameter space for inhomogeneous models in which a somewhat higher baryonic contribution to the closure density is possible than that allowed in standard homogeneous models. This result is contrary to some other recent studies and is due to both geometry and recently revised uncertainties in primordial light-element abundances, particularly {sup 7}Li. We find that the presently adopted abundance constraints are consistent with a contribution of baryons to the closure density as high as {Omega}{sub b}h{sub 50}{sup 2} {le} 0.11 ({eta} {le} 7 {times} 10{sup {minus}10}). This corresponds to a 20% increase over the limit from standard homogeneous models ({Omega}{sub b}h{sub 50}{sup 2} {le} 0.08, {eta} {le} 5.8 {times} 10{sup {minus}10}). With a high deuterium abundance the upper limits for the inhomogeneous and homogeneous models would be {Omega}{sub b}h{sub 50}{sup 2} {le} 0.04 and 0.03 ({eta} {le} 2.6 {times} 10{sup {minus}10} and 1.9 {times} 10{sup {minus}10}), respectively. Even higher limits could be obtained by further relaxing the presently accepted primordial lithium abundance constraint as some have proposed.
Date: July 20, 1995
Creator: Mathews, G.J.; Kajino, T. & Orito, M.
Partner: UNT Libraries Government Documents Department