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We show that for the discussed scenario of a neutron-star merger in highly neutronized ejecta (Y e ?0.1), neutron-induced fission plays a major role in the r-process cycling and is the main obstacle to the formation of superheavy elements. At the final stage of the r-process, when the free-neutron density is already too low to maintain rapid nucleosynthesis and only beta-decay and beta-delayed fission take place, the leading role in forming the final abundances of chemical elements passes to delayed fission. The latter ultimately changes the abundances of individual isotopes in the region before the second peak and heavier than lead, which, in particular, affects the determination of the age of the Galaxy. 相似文献
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N. H. M. Crighton J. K. Webb R. F. Carswell K. M. Lanzetta 《Monthly notices of the Royal Astronomical Society》2003,345(1):243-252
We report on a further analysis of the ratio of deuterium to hydrogen (D/H) using Hubble Space Telescope ( HST ) spectra of the z = 0.701 Lyman limit system towards the quasi-stellar object (QSO) PG1718+481. Initial analyses of this absorber found it gave a high D/H value, 1.8– 3.1 × 10−4 , inconsistent with several higher redshift measurements. It is thus important to critically examine this measurement. By analysing the velocity widths of the D i , H i and metal lines present in this system, Kirkman et al. report that the additional absorption in the blue wing of the Lyα line cannot be D i , with a confidence level of 98 per cent. Here we present a more detailed analysis, taking into account possible wavelength shifts between the three sets of HST spectra used in the analysis. We find that the constraints on this system are not as strong as those claimed by Kirkman et al. The discrepancy between the parameters of the blue wing absorption and the parameters expected for D i is marginally worse than 1σ.
Tytler et al. commented on the first analysis of Webb et al., reporting the presence of a contaminating lower redshift Lyman limit system, with log[ N (H i )] = 16.7 at z = 0.602 , which biases the N (H i ) estimate for the main system. Here we show that this absorber actually has log[ N (H i )] < 14.6 and does not impact on the estimate of N (H i ) in the system of interest at z = 0.701 .
The purpose of the present paper is to highlight important aspects of the analysis which were not explored in previous studies, and hence to help refine the methods used in future analyses of D/H in quasar spectra. 相似文献
Tytler et al. commented on the first analysis of Webb et al., reporting the presence of a contaminating lower redshift Lyman limit system, with log[ N (H i )] = 16.7 at z = 0.602 , which biases the N (H i ) estimate for the main system. Here we show that this absorber actually has log[ N (H i )] < 14.6 and does not impact on the estimate of N (H i ) in the system of interest at z = 0.701 .
The purpose of the present paper is to highlight important aspects of the analysis which were not explored in previous studies, and hence to help refine the methods used in future analyses of D/H in quasar spectra. 相似文献
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Hsu Wei-biao 《Chinese Astronomy and Astrophysics》2003,27(4):365-373
This paper reviews the evidence for short-lived radionuclides in the early solar system and evaluates the models of their origin. The stellar model requires that some freshly-nucleosynthesized radionuclides were injected into the proto-solar cloud shortly before it began to collapse. The spallation theory suggests that these nuclides were the products of interaction between energetic particles and gas/dust in the proto-solar cloud or solar nebula. A brief discussion is given to a new theory for the X-wind model of solar system formation. 相似文献
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Gary J. Sharpe 《Monthly notices of the Royal Astronomical Society》2001,322(3):614-624
The effect of curvature on detonation speed and structure for detonation waves in C–O is investigated. Weakly curved detonation fronts have a sonic point inside the reaction zone. In such waves the detonation speed depends on the detailed internal structure and not on simple jump conditions. Hence, in order to obtain the correct propagation speed and products of burning, the reaction length-scales must be resolved in any numerical simulation involving curved detonations in C–O. For each value of the initial density there is a corresponding extinction curvature above which quasi-steady detonations cannot propagate. For densities less than 2×107 g cm−3 , where the self-sustaining planar waves are Chapman–Jouguet, and for realistic values of the curvature, the sonic point moves from the end of silicon burning to the end of oxygen burning. Hence the effective detonation length, i.e. the length-scale of the burning between the shock and the sonic point which can affect the front, is several orders of magnitudes less than the planar waves predict. However, silicon burning, which occurs downstream of the sonic point, is increased in length by a few orders of magnitude owing to lower detonation speeds and temperatures. Therefore more intermediate-mass elements will be produced by incomplete burning if curvature is taken into account. Recent advances in detonation theory and modelling are also discussed in the context of Type Ia supernovae. 相似文献
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Yakiv V. Pavlenko Hugh R. A. Jones Andrew J. Longmore 《Monthly notices of the Royal Astronomical Society》2003,345(1):311-324
The behaviour of the Δν= 2 CO bands around 2.3 μm was examined by comparing observed and synthetic spectra in stars in globular clusters of different metallicity. Changes in the 12 C/13 C isotopic ratio and the carbon abundances were investigated in stars from 3500–4900 K in the galactic globular clusters M71, M5, M3 and M13, covering the metallicity range from −0.7 to −1.6. We found relatively low carbon abundances that are not affected by the value of oxygen abundance. For most giants, the 12 C/13 C ratios determined are consistent with the equilibrium value for the CN cycle. This suggests complete mixing on the ascent of the red giant branch, in contrast to the substantially higher values predicted across this range of parameters by the current generation of models. We found some evidence for a larger dispersion of 12 C/13 C in giants of M71 of metallicity [μ]=[M/H]=−0.7 in comparison with the giants of M3, M5 and M13, which are more metal deficient. Finally, we show evidence for lower 12 C/13 C in giants of globular clusters with lower metallicities, as predicted by theory. 相似文献
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Astronomy Letters - We discuss the possibility of elements heavier than iron being produced in the cooling central part of a low-mass supernova remnant in terms of a consistent kinetic model that... 相似文献