Showing papers on "Stellar nucleosynthesis published in 2007"
TL;DR: A review of the state-of-the-art in the field can be found in this paper, where the authors present a brief summary of the one- or multidimensional spherical or non-spherical explosion simulations available to date.
706 citations
TL;DR: In this article, the authors present a survey of nucleosynthesis that occurs in 32 stars of solar metallicity in the mass range 12 − 120 M ⊙, where the most recent set of solar abundances, opacities, mass loss rates, and current estimates of nuclear reaction rates are employed.
683 citations
TL;DR: In this article, the authors investigated the effects of background line opacities due to atomic lines on the statistical equilibrium of Fe in late-type stars using 3D hydrodynamical model stellar atmospheres.
Abstract: The information about the chemical compositions of stars is encoded in their spectra Accurate determinations of these compositions are crucial for our understanding of stellar nucleosynthesis and Galactic chemical evolution The determination of elemental abundances in stars requires models for the stellar atmospheres and the processes of line formation Nearly all spectroscopic analyses of late-type stars carried out today are based on one-dimensional (1D), hydrostatic model atmospheres and on the assumption of local thermodynamic equilibrium (LTE) This approach can lead to large systematic errors in the predicted stellar atmospheric structures and line-strengths, and, hence, in the derived stellar abundances In this thesis, examples of departures from LTE and from hydrostatic equilibrium are explored The effects of background line opacities (line-blocking) due to atomic lines on the statistical equilibrium of Fe are investigated in late-type stars Accounting for this line opacity is important at solar metallicity, where line-blocking significantly reduces the rates of radiatively induced ionizations of Fe On the contrary, the effects of line-blocking in metal-poor stars are insignificant In metal-poor stars, the dominant uncertainty in the statistical equilibrium of Fe is the treatment of inelastic H+Fe collisions Substantial departures of Fe abundances from LTE are found at low metallicities: about 03 dex with efficient H+Fe collisions and about 05 dex without The impact of three-dimensional (3D) hydrodynamical model atmospheres on line formation in red giant stars is also investigated Inhomogeneities and correlated velocity fields in 3D models and differences between the mean 3D stratifications and corresponding 1D model atmospheres can significantly affect the predicted line strengths and derived abundances, in particular at very low metallicities In LTE, the differences between 3D and 1D abundances of C, N, and O derived from CH, NH, and OH weak low-excitation lines are in the range -05 dex to -10 dex at [Fe/H]=-3 Large negative corrections (about -08 dex) are also found in LTE for weak low-excitation neutral Fe lines We also investigate the impact of 3D hydrodynamical model stellar atmospheres on the determination of elemental abundances in the carbon-rich, hyper iron-poor stars HE 0107-5240 and HE 1327-2326 The lower temperatures of the line-forming regions of the 3D models compared with 1D models cause changes in the predicted spectral line strengths In particular we find the 3D abundances of C, N, and O to be lower by about -08 dex (or more) than estimated from a 1D analysis The 3D abundance of Fe is decreased but only by -02 dex Departures from LTE for Fe might actually be very large for these stars and dominate over the effects due to granulation
227 citations
TL;DR: Based on non-correlation trends between elemental abundances as a function of Eu richness in a large sample of metal-poor stars, it is shown that mixing of a consistent and robust light element primary process (LEPP) and the r-process pattern found in r-II metalpoor stars explains such apparent nonuniformity as discussed by the authors.
Abstract: Recent observations of r-process-enriched metal-poor star abundances reveal a nonuniform abundance pattern for elements -->Z ≤ 47. Based on noncorrelation trends between elemental abundances as a function of Eu richness in a large sample of metal-poor stars, it is shown that the mixing of a consistent and robust light element primary process (LEPP) and the r-process pattern found in r-II metal-poor stars explains such apparent nonuniformity. Furthermore, we derive the abundance pattern of the LEPP from observation and show that it is consistent with a missing component in the solar abundances when using a recent s-process model. As the astrophysical site of the LEPP is not known, we explore the possibility of a neutron-capture process within a site-independent approach. It is suggested that scenarios with neutron densities -->nn ≤ 1013 cm−3 or in the range -->nn ≥ 1024 cm−3 best explain the observations.
172 citations
TL;DR: In this paper, the nuclear structure in regions of the Segre chart which are of astrophysical importance is reviewed and the main emphasis is put on those nuclei that are relevant for stellar nucleosynthesis in fusion processes, and in slow neutron capture, both located close to stability, rapid neutron capture close to the neutron dripline and rapid proton capture near the proton dripler.
Abstract: The nuclear structure in regions of the Segre chart which are of astrophysical importance is reviewed. The main emphasis is put on those nuclei that are relevant for stellar nucleosynthesis in fusion processes, and in slow neutron capture, both located close to stability, rapid neutron capture close to the neutron dripline and rapid proton capture near the proton dripline. The basic features of modern nuclear structure, their importance and future potential for astrophysics and their level of predictibility are critically discussed. Recent experimental and theoretical results for shell evolution far off the stability line and consequences for weak interaction processes, proton and neutron capture are reviewed.
159 citations
TL;DR: In this article, the authors explored the dependence of presupernova evolution and supernova nucleosynthesis yields on the uncertainties in helium-burning reaction rates and found that the revised solar abundances of Lodders for the initial stellar composition, instead of those of Anders and Grevesse, changes the supernova yields and limits the constraints that those yields place on the 12C(α,γ)16O reaction rate.
Abstract: We explore the dependence of presupernova evolution and supernova nucleosynthesis yields on the uncertainties in helium-burning reaction rates. Using the revised solar abundances of Lodders for the initial stellar composition, instead of those of Anders and Grevesse, changes the supernova yields and limits the constraints that those yields place on the 12C(α,γ)16O reaction rate. The production factors of medium-weight elements (A = 16-40) were found to be in reasonable agreement with observed solar ratios within the current experimental uncertainties in the triple-α reaction rate. Simultaneous variations by the same amount in both reaction rates or in either of them separately, however, can induce significant changes in the central 12C abundance at core carbon ignition and in the mass of the supernova remnant. It therefore remains important to have experimental determinations of the helium-burning rates so that their ratio and absolute values are known with an accuracy of 10% or better.
68 citations
TL;DR: A very large amount of nuclear information is necessary in order to model the rapid neutron capture process of stellar nucleosynthesis as mentioned in this paper, and the enormously challenging experimental and theoretical task imposed by all these requirements is reviewed, and the state-of-theart development in the field is presented.
Abstract: The r-process, or the rapid neutron-capture process, of stellar nucleosynthesis is called for to explain the production of the stable (and some long-lived radioactive) neutron-rich nuclides heavier than iron that are observed in stars of various metallicities, as well as in the solar system.
A very large amount of nuclear information is necessary in order to model the r-process. This concerns the static characteristics of a large variety of light to heavy nuclei between the valley of stability and the vicinity of the neutron-drip line, as well as their beta-decay branches or their reactivity. The enormously challenging experimental and theoretical task imposed by all these requirements is reviewed, and the state-of-the-art development in the field is presented. Nuclear-physics-based and astrophysics-free r-process models of different levels of sophistication have been constructed over the years. We review their merits and their shortcomings. For long, the core collapse supernova of massive stars has been envisioned as the privileged r-process location. We present a brief summary of the one- or multidimensional spherical or non-spherical explosion simulations available to-date. Their predictions are confronted with the requirements imposed to obtain an r-process. The possibility of r-nuclide synthesis during the decompression of the matter of neutron stars following their merging is also discussed.
53 citations
TL;DR: In this paper, the authors compute self-consistent chemical evolution models taking into account the results of updated stellar nucleosynthesis and conclude that massive stars are the major factor responsible for the production of copper in ω Cen as well as the Galactic disc.
Abstract: Despite the many studies on stellar nucleosynthesis published so far, the scenario for the production of copper in stars remains elusive. In particular, it is still debated whether copper originates mostly in massive stars or in Type Ia supernovae. To answer this question, we compute self-consistent chemical evolution models taking into account the results of updated stellar nucleosynthesis. By contrasting copper evolution in ω Cen and the Milky Way, we end up with a picture where massive stars are the major factor responsible for the production of copper in ω Cen as well as the Galactic disc.
52 citations
TL;DR: In this article, the authors compute self-consistent chemical evolution models taking into account the results of updated stellar nucleosynthesis, and they end up with a picture where massive stars are the major responsible for the production of Cu in Omega Cen as well as the Galactic disc.
Abstract: Despite the many studies on stellar nucleosynthesis published so far, the scenario for the production of Cu in stars remains elusive. In particular, it is still debated whether copper originates mostly in massive stars or type Ia supernovae. To answer this question, we compute self-consistent chemical evolution models taking into account the results of updated stellar nucleosynthesis. By contrasting copper evolution in Omega Cen and the Milky Way, we end up with a picture where massive stars are the major responsible for the production of Cu in Omega Cen as well as the Galactic disc.
46 citations
TL;DR: The first discovery of argon in hot evolved stars and white dwarfs was reported in this paper, where the authors identified the Ar vii 1063.55 A line in some of the hottest known (Teff = 95 000−110 000 K) central stars of planetary nebulae and (pre-) white- dwarfs of various spectral type.
Abstract: Context. We report the first discovery of argon in hot evolved stars and white dwarfs. We have identified the Ar vii 1063.55 A line in some of the hottest known (Teff = 95 000−110 000 K) central stars of planetary nebulae and (pre-) white dwarfs of various spectral type. Aims. We determine the argon abundance and compare it to theoretical predictions from stellar evolution theory as well as from diffusion calculations. Methods. We analyze high-resolution spectra taken with the Far Ultraviolet Spectroscopic Explorer. We use non-LTE line-blanketed model atmospheres and perform line-formation calculations to compute synthetic argon line profiles. Results. We find a solar argon abundance in the H-rich central star NGC 1360 and in the H-deficient PG 1159 star PG 1424+535. This confirms stellar evolution modeling that predicts that the argon abundance remains almost unaffected by nucleosynthesis. For the DAO-type central star NGC 7293 and the hot DA white dwarfs PG 0948+534 and RE J1738+669 we find argon abundances that are up to three orders of magnitude smaller than predictions of calculations assuming equilibrium of radiative levitation and gravitational settling. For the hot DO white dwarf PG 1034+001 the theoretical overprediction amounts to one dex. Conclusions. Our results confirm predictions from stellar nucleosynthesis calculations for the argon abundance in AGB stars. The argon abundance found in hot white dwarfs, however, is another drastic example that the current state of equilibrium theory for trace elements fails to explain the observations quantitatively.
45 citations
TL;DR: In this paper, the authors used updated experimental and theoretical nuclear-physics data and performed detailed r-process calculations within the classical, site-independent "waiting-point" approximation and the "neutrino-wind" scenario of core-collapse type II supernovae (SNII).
TL;DR: In this article, the authors present an overview of the current understanding of these topics emphasizing the insights that have been gained through investigations in the charge and energy ranges Z≲30 and E/M≲1 GeV/nuc, and particularly those using data obtained from the Cosmic Ray Isotope Spectrometer on NASA's Advanced Composition Explorer mission.
Abstract: The galactic cosmic rays arriving near Earth, which include both stable and long-lived nuclides from throughout the periodic table, consist of a mix of stellar nucleosynthesis products accelerated by shocks in the interstellar medium (ISM) and fragmentation products made by high-energy collisions during propagation through the ISM. Through the study of the composition and spectra of a variety of elements and isotopes in this diverse sample, models have been developed for the origin, acceleration, and transport of galactic cosmic rays. We present an overview of the current understanding of these topics emphasizing the insights that have been gained through investigations in the charge and energy ranges Z≲30 and E/M≲1 GeV/nuc, and particularly those using data obtained from the Cosmic Ray Isotope Spectrometer on NASA’s Advanced Composition Explorer mission.
TL;DR: In this article, the authors use the Cambridge stellar evolution code STARS to model the evolution and nucleosynthesis of zero-metallicity intermediate-mass stars and investigate the effect of duplicity on the nucleosynthetic output of these systems and the potential abundances of the secondaries.
Abstract: We use the Cambridge stellar evolution code STARS to model the evolution and nucleosynthesis of zero-metallicity intermediate-mass stars. We investigate the effect of duplicity on the nucleosynthesis output of these systems and the potential abundances of the secondaries. The surfaces of zero-metallicity stars are enriched in CNO elements after second dredge-up. During binary interaction, such as Roche lobe overflow or wind accretion, metals can be released from these stars and the secondaries enriched in CNO isotopes. We investigate the formation of the two most metal poor stars known, HE 0107-5240 and HE 1327-2326. The observed carbon and nitrogen abundances of HE 0107-5240 can be reproduced by accretion of material from the companion-enhanced wind of a 7-M ⊙ star after second dredge-up, though oxygen and sodium are underproduced. We speculate that HE 1327-2326, which is richer in nitrogen and strontium, may similarly be formed by wind accretion in a later asymptotic giant branch phase after third dredge-up.
TL;DR: In this paper, the authors measured the titanium isotopic compositions of 23 silicon carbide grains from the Orgueil (CI) carbonaceous chondrites and compared the results to the results of several published stellar models that employ different values for some important parameters.
Abstract: We have measured the titanium isotopic compositions of 23 silicon carbide grains from the Orgueil (CI) carbonaceous chondrites for which isotopic compositions of silicon, carbon, and nitrogen and aluminum-magnesium systematics had been measured previously. Using the 16 mostprecise measurements, we estimate the relative contributions of stellar nucleosynthesis during the asymptotic giant branch (AGB) phase and the initial compositions of the parent stars to the compositions of the grains. To do this, we compare our data to the results of several published stellar models that employ different values for some important parameters. Our analysis confirms that s-process synthesis during the AGB phase only slightly modified the titanium compositions in the envelopes of the stars where mainstream silicon carbide grains formed, as it did for silicon. Our analysis suggests that the parent stars of the >1 μm silicon carbide grains that we measured were generally somewhat more massive than the Sun (2-3 Mʘ) and had metallicities similar to or slightly higher than solar. Here we differ slightly from results of previous studies, which indicated masses at the lower end of the range 1.5-3 Mʘ and metallicities near solar. We also conclude that models using a standard 13C pocket, which produces a good match for the main component of s-process elements in the solar system, overestimate the contribution of the 13C pocket to s-process nucleosynthesis of titanium found in silicon carbide grains. Although previous studies have suggested that the solar system has a significantly different titanium isotopic composition than the parent stars of silicon carbide grains, we find no compelling evidence that the Sun falls off of the array defined by those stars. We also conclude that the Sun does lie on the low-metallicity end of the silicon and titanium arrays defined by mainstream silicon carbide grains.
TL;DR: In this article, the abundance of the light isotope of helium, 3He, was determined from measurements of the hyperfine transition of 3He+ which has a rest wavelength of 3.46 cm (8.665 GHz).
Abstract: We are making precise determinations of the abundance of the light isotope of helium, 3He. The 3He abundance in Milky Way sources impacts stellar evolution, chemical evolution, and cosmology. The abundance of 3He is derived from measurements of the hyperfine transition of 3He+ which has a rest wavelength of 3.46 cm (8.665 GHz). As with all the light elements, the present interstellar 3He abundance results from a combination of Big Bang Nucleosynthesis (BBNS) and stellar nucleosynthesis. We are measuring the 3He abundance in Milky Way H ii regions and planetary nebulae (PNe). The source sample is currently comprised of 60 H ii regions and 12 PNe. H ii regions are examples of zero-age objects that are young relative to the age of the Galaxy. Therefore their abundances chronicle the results of billions of years of Galactic chemical evolution. PNe probe material that has been ejected from low-mass (M≤ 2M ⊙) to intermediate-mass (M∼2–5M ⊙) stars to be further processed by future stellar generations. Because the Milky Way ISM is optically thin at centimeter wavelengths, our source sample probes a larger volume of the Galactic disk than does any other light element tracer of Galactic chemical evolution. The sources in our sample possess a wide range of physical properties (including object type, size, temperature, excitation, etc.). The 3He abundances we derive have led to what has been called “The 3He Problem”.
TL;DR: In this paper, the impact of new results for neutron capture cross sections on light and medium mass nuclei is discussed, and a better characterization of the weak s component would help to disentangle the various processes contributing to element production in this region.
TL;DR: In this paper, a detailed study with modern analytical tools, of isotopic signatures in particular, provides highly accurate and detailed information with regard to stellar nucleosynthesis and grain formation in stellar atmospheres.
Abstract: Small amounts of pre-solar “stardust” grains have survived in the matrices of primitive meteorites and interplanetary dust particles. These grains—formed directly in the outflows of or from the ejecta of stars—include thermally and chemically refractory carbon materials such as diamond, graphite and silicon carbide; as well as refractory oxides and nitrides. Pre-solar silicates, which have only recently been identified, are the most abundant type except for possibly diamond. The detailed study with modern analytical tools, of isotopic signatures in particular, provides highly accurate and detailed information with regard to stellar nucleosynthesis and grain formation in stellar atmospheres. Important stellar sources are Red Giant (RG) and Asymptotic Giant Branch (AGB) stars, with supernova contributions apparently small. The survival of those grains puts constraints on conditions they were exposed to in the interstellar medium and in the early solar system.
TL;DR: Observations of 3He in planetary nebulae, however, indicate that some stars produce prodigious amounts of3He, inconsistent with the claim that all low-mass stars should destroy 3He.
Abstract: Eggleton et al . (Reports, 8 December 2006, p. 1580) reported on a deep-mixing mechanism in low-mass stars caused by a Rayleigh-Taylor instability that destroys all of the helium isotope 3He produced during the star's lifetime. Observations of 3He in planetary nebulae, however, indicate that some stars produce prodigious amounts of 3He. This is inconsistent with the claim that all low-mass stars should destroy 3He.
01 Jan 2007
TL;DR: In this article, the authors investigated the role of neutrino/antineutrino captures on free nucleons and on nuclei, electron/positron captures, and β − /β + -decays in core collapse supernova explosions.
Abstract: The problem of core collapse supernova explosions is long standing and attempts to understand the mechanism have been ongoing. On one hand, a full understanding of the underlying mechanism is still pending. On the other hand, there is a need to provide correct nucleosynthesis abundances for the progressing fields of galactic evolution and observations of low-metallicity stars. Traditionally, nucleosynthesis predictions rely on artificially induced explosions which is justifiable for the outer stellar layers but does not account for the effects in the innermost ejecta directly related to the explosion mechanism. The composition of the innermost ejecta is directly linked to the electron fraction Ye = Z/A . This dissertation contains the first investigation of explosive core collapse nucleosynthesis which consistently includes all weak interactions responsible for changes in Ye (neutrino/antineutrino captures on free nucleons and on nuclei, electron/positron captures, and β − /β + -decays). A second novelty of the nucleosynthesis calculations in this thesis is that they are based on core collapse models where the mass cut emerges consistently from the simulation. This is of importance for predicting the amount of Fe-group elements ejected (this is a free parameter in explosions induced by means of a thermal bomb or piston and has to be constrained from observations). Two different approaches are used to achieve explosions (in otherwise non-explosive models): We apply parametrized variations to the neutrino absorption cross sections in order to mimic in one dimension the possible increase of neutrino luminosities caused by uncertainties in proto-neutron star convection in a multi-D scenario. Alternatively, we apply parametrized variations to the neutrino absorption cross section on nucleons in the gain region to mimic the increased neutrino energy deposition which convective turnover of matter in the gain region is expected to provide. We find that both measures lead to explosions and that Ye > 0.5 in the innermost ejected layers (i.e. a proton-rich environment). The nucleosynthesis calculations show that • The proton-rich environment results in enhanced abundances of 45 Sc, 49 Ti, and by chemical evolution studies and observations of low-metallicity stars.
• Antineutrino absorption reactions in the proton-rich environment produce neutrons which are immediately captured by neutron-deficient nuclei. • A new nucleosynthesis process (νp-process) takes places in supernovae (and possibly gamma-ray bursts) allowing for appreciable synthesis of elements with mass numbers A > 64. • The νp-process is a candidate for explaining the large Sr abundance seen in a hyper-metal poor star, for the suggested lighter element primary process, and possibly for the origin of the solar abundances of the light p-nuclei.
01 Jun 2007-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: Experimental reaction rates are the necessary nuclear physics input for quantitative studies of nucleosynthesis during the hydrostatic phases of stellar evolution as well as in explosive scenarios such as novae, X-ray burster, or supernovae as discussed by the authors.
Abstract: Experimental reaction rates are the necessary nuclear physics input for quantitative studies of nucleosynthesis during the hydrostatic phases of stellar evolution as well as in explosive scenarios such as novae, X-ray burster, or supernovae. Such studies represent crucial tests of the respective astrophysical models, which themselves constitute the basis for our understanding of the history of the Universe. The status of the nuclear input data and the present experimental approaches are illustrated at the example of the slow neutron capture process (s process). Accelerator mass spectroscopy bears promising possibilities for measurements of crucial reaction rates in this field, which would be extremely difficult to determine otherwise.
TL;DR: In this article, the authors review the information that planetary nebulae and their immediate progenitors, the post-AGB objects, can provide to probe the nucleosynthesis and mixing in low and intermediate mass stars.
Abstract: We review the information that planetary nebulae and their immediate progenitors, the post-AGB objects, can provide to probe the nucleosynthesis and mixing in low and intermediate mass stars We emphasize new approaches based on high signal-to-noise spectroscopy of planetary nebulae and of their central stars We mention some of the problems still to overcome We emphasize that, as found by several authors, planetary nebulae in low metallicity environments cannot be used to probe the oxygen abundance in the interstellar medium out of which their progenitors were formed, because of abundance modification during stellar evolution
TL;DR: In this paper, the basic theory of nuclear reactions in stars and sketch the general rules of stellar evolution are presented, and the subject of supernova explosions both by core collapse in massive stars and carbon-deflagration in binary systems when one of the components is a White Dwarf accreting mass from the companion stars (type Ia).
Abstract: We present the basic theory of nuclear reactions in stars and sketch
the general rules of stellar evolution. Then we shortly review the
subject of supernova explosions both by core collapse in massive
stars (type II) and carbon-deflagration in binary systems when one
of the components is a White Dwarf accreting mass from the companion
(type Ia). We also present elementary notions of s- and r-process
nucleo-synthesis. Finally, we shortly review the topic of galactic
chemical evolution and highlight some simple solutions aimed at
understanding the main observational data on abundances and
abundance ratios.
Posted Content•
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TL;DR: In this article, the basic ingredients of galactic chemical evolution and the mechanisms of galaxy formation were described and compared using both analytical and numerical models, and the results for the Milky Way, Dwarf Irregulars, Quasars and Intra-Cluster Medium with abundances derived from emission lines.
Abstract: In this series of lectures we first describe the basic ingredients of galactic chemical evolution and discuss both analytical and numerical models Then we compare model results for the Milky Way, Dwarf Irregulars, Quasars and the Intra-Cluster- Medium with abundances derived from emission lines These comparisons allow us to put strong constraints on the stellar nucleosynthesis and the mechanisms of galaxy formation
01 Mar 2007
TL;DR: In this article, a simple galactic evolution model for producing and preserving the observed mass-independent oxygen isotope variations in solar system materials is described, which is the current favorite mechanism for explaining the mass independent fractionation of O isotopes in primitive meteorites.
Abstract: Introduction: The three isotopes of oxygen (O, O and O) are produced by different nucleosynthetic processes. The major isotope, O, is produced in supernovae and is the most abundant product of primary galactic nucleosynthesis. The two more abundant elements, H and He, were produced by the Big Bang nucleosynthesis. Clayton et al. [1] discovered large, mass independent variations in O relative to both O and O in primitive meteorites. Solar System oxygen is now known to be isotopically heterogeneous on all spatial scales, from sub-micron-sized grains to planets. The origin of this isotopic heterogeneity is still unresolved. The lack of correlated nucleosynthetic anomalies in isotopes of major elements such as Mg and Si along with the lack of O-pure presolar grains lead Clayton [2] to abandon the original idea that the mass independent fractionation line results from mixing with a O pure supernova end member. The current favorite mechanism for explaining the mass independent fractionation of O isotopes in primitive meteorites is selfshielding of carbon monoxide during UV photo dissociation at different astrophysical settings [2, 3, 4]. Here we describe a simple galactic evolution model for producing and preserving the observed mass-independent oxygen isotope variations in solar system materials. Condensation of Oxygen: Condensation from a gas of average galactic composition produces three major oxygen reservoirs relevant to this study: (1) hightemperature Al, Ca, Ti-enriched refractory phases (~ 1 % of total O) commonly referred to as CAIs, (2) a ‘silicate dust’ (~ 14 % of total O) consisting mainly of ferromagnesian silicates, olivine and low-Ca pyroxene, and products of their hydration formed in the mid-and low-temperature range, and (3) the residual gas enriched in H, He, O, C, and N (~86 % of total O), with the last three elements capable of condensing as ices at very low temperatures. Because stellar nucleosynthesis led to predictable changes in the average Galactic elemental abundances with time [5], it is instructive to study whether and how such changes would affect the partitioning of O among different reservoirs. Figure 1 shows the condensation curves of oxygen from a gas of galactic average composition at 100 Ma, 1 Ga and 10 Ga (time of Solar System formation) after the Galaxy formation. These were calculated at total pressure of 10 bar using ZONMET [6]. The calculation at 10 Ga uses the composition of the Solar System [7] while for earlier times the average Galaxy compositions were obtained from [5]. The overall condensation trend of O remains the same; a shift of condensation curves to higher temperatures as the Galaxy gets older is due to the increase of ‘metal’/H+He ratio with time.
TL;DR: Nuclear fusion reactions generate the energies by which stars stabilize during their long lives in hydrostatic equilibrium as discussed by the authors, and during core collapse of massive stars nuclear reactions mediated by the weak force are essential.
31 Oct 2007
TL;DR: A review of the current literature on the LEPP and derived abundance pattern as a function of mass number is given in this article. But the LPP process is not considered in this paper.
Abstract: Observations of metal‐poor stars in the last decade have revealed an abundance pattern that have recently been explained as the result of two nucleosynthesis processes, a strong r‐process that creates most of the Z⩾56 and some 38⩽Z⩽47 abundances and a light element primary process (LEPP) responsible for creating the remaining 38⩽Z⩽47 abundances and some small contribution to heavier elements. We review some of the current literature on the LEPP and show a derived abundance pattern as a function of mass number.
Book Chapter•
01 Jan 2007
TL;DR: In this paper, the primary and secondary contributions to the arriving abundances for isotopes of elements between B and Ni were extracted by using measurements of cosmic-ray elemental and isotopic composition obtained from the Advanced Composition Explorer (ACE) spacecraft, a data base of measured and calculated fragmentation cross sections, and a leaky box model of interstellar propagation.
Abstract: The arriving abundances of a variety of cosmic-ray nuclides consist of comparable amounts of primary material produced by stellar nucleosynthesis and secondary matter resulting from fragmentation of heavier nuclei by collisions during interstellar propagation. In order to utilize such species in studies of cosmic-ray source composition it is necessary to determine the secondary fraction present in the arriving material and to assess the uncertainty in this determination. We have extracted the primary and secondary contributions to the arriving abundances for isotopes of elements between B and Ni by using 1) measurements of cosmic-ray elemental and isotopic composition obtained from the Cosmic Ray Isotope Spectrometer (CRIS) instrument on the Advanced Composition Explorer (ACE) spacecraft, 2) a data base of measured and calculated fragmentation cross sections, and 3) a leaky box model of interstellar propagation. We present derived decompositions and discuss their implications for studies of the composition of cosmic-ray source material. This work was supported by NASA at Caltech (under grant NAG5-12929), JPL, Washington University, and GSFC.
Posted Content•
TL;DR: In this paper, the authors calculate the contribution from the neutron-rich pockets in the hot convective bubbles of a core-collapse supernova and show that they do not contribute significantly to the total nucleosynthesis.
Abstract: Recent nucleosynthesis calculations of Type II supernovae using advanced neutrino transport determine that the early neutrino winds are proton-rich. However, a fraction of the ejecta emitted at the same time is composed of neutron-rich pockets. In this paper we calculate the nucleosynthesis contribution from the neutron-rich pockets in the hot convective bubbles of a core-collapse supernova and show that they do not contribute significantly to the total nucleosynthesis.
26 Nov 2007
TL;DR: In this article, the effect of variation of fundamental couplings and mass scales on primordial nucleosynthesis was analyzed in a systematic way, and the response of primordial element abundances to the variation of a large number of nuclear physics parameters, including nuclear binding energies, was established.
Abstract: We analyze the effect of variation of fundamental couplings and mass scales on primordial nucleosynthesis in a systematic way The first step establishes the response of primordial element abundances to the variation of a large number of nuclear physics parameters, including nuclear binding energies We find a strong influence of the n‐p mass difference, of the nucleon mass and of A = 3,4,7 binding energies A second step relates the nuclear parameters to the parameters of the Standard Model of particle physics The deuterium, and, above all, 7Li abundances depend strongly on the average light quark mass We calculate the behaviour of abundances when variations of fundamental parameters obey relations arising from grand unification We also discuss the possibility of a substantial shift in the lithium abundance while the deuterium and 4He abundances are only weakly affected
TL;DR: In this paper, the effect of electron screening on the Gamow-Teller resonant transition was investigated based on the shell model of nuclei, and it was shown that the electron screening increases the β-decay rate evidently at low temperatures and high densities.