共查询到20条相似文献，搜索用时 31 毫秒
1.
D. C. V. Mallik 《Journal of Astrophysics and Astronomy》1981,2(2):171-185
The current rate of nucleosynthesis in the solar neighbourhood is re-evaluated on the basis of Arnett’s (1978) stellar yields,
the mass loss models of Chiosi, Nasi and Sreenivasan (1978) and the initial mass function determined by Lequeux (1978). If
massive stars are held responsible for most of the metals we observe, a higher birthrate of these stars in the past is indicated
in view of the low current rate of nucleosynthesis. The intermediate mass stars may not supply the bulk of the metals unless
total disruption of their carbon core takes place.
While a declining birthrate is in conflict with the result obtained from the age-metallicity relation of stars, it is supported
by some galactic evolution models which interpret successfully the white dwarf mass distribution data. If the constraint of
a nearly time-invariant birthrate were strictly accepted, then models of the prompt initial enrichment type are required to
explain the observed abundances in terms of nucleosynthesis in massive stars. 相似文献
2.
I. V. Panov I. Yu. Korneev G. Martinez-Pinedo F. -K. Thielemann 《Astronomy Letters》2013,39(3):150-160
The formation of heavy elements in the neutron star merger scenario is considered. In such a scenario, the duration of the r-process is long and when the nucleosynthesis wave passes through the region of actinides, beta-delayed, neutron-induced, and spontaneous fission are added to the main r-process reaction channels. The dependence of the formation of superheavy elements on spontaneous fission model is investigated numerically. The formation of nuclei lighter than the cadmium-peak elements and cosmochronometer nuclei is shown to depend on strongly on the spontaneous fission model used in nucleosynthesis calculations. The regions of nuclei with short spontaneous fission half-lives prevent the formation of superheavy elements in the r-process, but the prediction of their yields is so far inaccurate because of an insufficient accuracy of calculating a number of transactinide parameters. The relative contributions from neutron-induced, beta-delayed, and spontaneous fission have been determined for various spontaneous fission models in the nucleosynthesis scenario considered. 相似文献
3.
Donald D. Clayton 《Meteoritics & planetary science》1992,27(1):5-17
Abstract— The science of nucleosynthesis was substantially inspired by chemical analyses of meteorites. As if in repayment, that theory now imbues meteoritics with enlarged meaning. I recount the emergence of four great issues for nucleosynthesis—issues that received decades of my own attention; and I describe unexpected abundance patterns within meteorites that were suggested by the resolution of those issues. The latter have altered the information content of meteoritic science. The issues are: 1. a quantitative s-process theory 2. cosmoradiogenic chronology 3. explosive nucleosynthesis and gamma-ray astronomy 4. cosmic chemical memory Starting from historical origins for each issue, I comment upon both the broad cultural canvas in which they lie and my own work in their establishment. Examples of predicted (or rationalized) meteoritic measurements illustrate our surprised delight at the expansion of the range and power of meteoritic science. 相似文献
4.
The chemical enrichment in the galactic halo is studied, on the basis of the numerical model developed in Paper I, with paricular attention to the overabundances of O and light elements with respect to Fe shown by metal poor stars. Some representative nucleosynthesis pictures for stars of both Population I and Population II are considered and their yields are compared with observations of relative abundances in the Sun and in the halo, to identify the possible reasons of the observed compositional differences. It is found that solar elemental ratios can be reproduced if intermediate mass stars are allowed to give some contribution to the production of Fe by type-I supernovae, while the ratios of abundances observed in the halo are more similar to the relative yields produced by massive stars. These features are shared by all the nucleosynthesis schemes which have been considered. Using the best model of Paper I, we show that the steep star formation induced by the collapse has a decisive effect in maintaining the overabundances of light elements during the whole evolution of the halo. The relevance of this conclusion is discussed also in the light of a possible interpretation of the differences between the two abundance scales for globular clusters. 相似文献
5.
We study the effects of possible deviations of fundamental physical constants on the yields of light nuclides, 2D, 3He, 4He, 7Li, and others during primordial nucleosynthesis. The deviations of fundamental constants from their current values are considered in the low-energy approximation of string theories; the latter predict the existence of a scalar field, which, apart from the tensor gravitational field, determines the space geometry. A two-parameter (η, δ) model is constructed for primordial nucleosynthesis: η = n B /n γ is the baryon-to-photon density ratio, and Ω is the relative deviation of fundamental physical constants at the epoch of primordial nucleosynthesis from their current values. A dependence of η on the deviation of coupling constants Ω has been derived on condition that the primordial helium abundance is Y p = f(η, δ) = const, where const corresponds to experimental values. We thus showed that the relative baryonic density (and hence ΩB could vary over a much wider range than allowed by the standard nucleosynthesis model. Considering this result, we discuss the recently found mismatch between ΩB obtained from an analysis of CMBR anisotropy and from the standard primordial nucleosynthesis model. 相似文献
6.
《New Astronomy Reviews》2000,44(4-6):321-327
We have extended our evolutionary synthesis models for Star Forming Regions to the γ-ray domain. Applying different yields to the resulting synthetic populations, we obtain lightcurves of γ-ray line emission due to the radioactive decay of stellar nucleosynthesis products, such as 26Al and 60Fe. We present here this time evolution and the application of the models to regions of star formation in our galaxy. 相似文献
7.
综述了近扯为ＡＧＢ星核合成的理论研究情况，包括轻，重核素核合成理论，ＡＧＢ星的分类，ＡＧＢ星的演化特征，ＡＧＢ星内的元素核合成理论的研究及外赋ＭＳ，Ｓ 双星吸积机制的研究情况。 相似文献
8.
We analyse two recent computations of Type II supernova nucleosynthesis by Woosley & Weaver (hereafter WW95) and Thielemann, Nomoto & Hashimoto (hereafter TNH96), focusing on the ability to reproduce the observed [Mg/Fe] ratios in various galaxy types. We show that the yields of oxygen and total metallicity are in good agreement. However, TNH96 models produce more magnesium in the intermediate and less iron in the upper mass range of Type II supernovae than WW95 models. To investigate the significance of these discrepancies for chemical evolution, we calculate simple stellar population yields for both sets of models and different initial mass function slopes. We conclude that the Mg yields of WW95 do not suffice to explain the [Mg/Fe] overabundance either in giant elliptical galaxies and bulges or in metal-poor stars in the solar neighbourhood and the Galactic halo. Calculating the chemical evolution in the solar neighbourhood according to the standard infall model, we find that, using WW95 and TNH96 nucleosynthesis, the solar magnesium abundance is underestimated by 29 and 7 per cent, respectively. We include the relaxation of the instantaneous mixing approximation in chemical evolution models by splitting the gas component into two different phases. In additional simulations of the chemical evolution in the solar neighbourhood, we discuss various time-scales for the mixing of the stellar ejecta with the interstellar medium. We find that a delay of the order of 108 yr leads to a better fit of the observational data in the [Mg/Fe]–[Fe/H] diagram without destroying the agreement with solar element abundances and the age–metallicity relation. 相似文献
9.
10.
在提出的贫金属星中子俘获元素丰度的计算模型基础上研究1999年新发表的21颗贫金属星的中子俘获元素丰度分布。结果表明，对较重的中子俘获元素理论预测曲线与观测值符合得很好，而对较轻的中子俘获元素二者有所偏离。这表明在贫金属环境下，对较重的中子俘获元素各核合成过程产生的丰度分布与太阳系中相应过程的丰度分布相似，但贡献比例与太阳系不同；而对较轻的中子俘获元素丰度分布与太阳系的丰度分布有所偏离；这也说明较轻的和较重的中子俘获元素的核合成场所不同，即具有不同的核合成机制。同时还特别讨论了丰度观测误差对表征各核合成过程的分量系数的影响。 相似文献
11.
Wen-Yuan Cui Bo Zhang Ya-Min Quan Gui-De Zhou Yan-Ping Chen 《Astrophysics and Space Science》2008,314(4):351-359
Taking account of the metallicity dependence of the s-process nucleosynthesis in the AGB stars, we adopted the wind accretion
model with the condition of total angular momentum conservation and used the Monte-Carlo method to study the variations and
the distributions of the orbital elements of the mild and strong Ba stars. The calculated results show that the level of heavy-element
overabundance in a Ba star depends on the orbital period. Since there is a strong dependence of s-process yields on the initial
stellar metallicity of the AGB star and a strong increase of the s-process yields in AGB stars with decreasing metallicity,
the calculated results strongly suggest that the initial metallicity of the Ba star systems is another important parameter
for the level of heavy-element overabundance in a Ba star. The strong Ba stars generally have lower metallicities than mild
Ba stars. The masses of AGB progenitor and Ba star are other two parameters which also have some impact on the heavy-element
overabundance in the Ba star. 相似文献
12.
13.
We have determined the solar abundances of the rare earths (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Tm, Yb, Lu) on the basis of measurements made on new high-resolution tracings of the solar spectrum obtained at the International Scientific Station of the Jungfraujoch (Switzerland) by L. Delbouille, L. Neven and G. Roland. Our results (Table XV) are compared with those of other authors for the sun and meteorites as well as with the abundances predicted by nucleosynthesis theories. 相似文献
14.
Zhe Chen Jiang Zhang YanPing Chen WenYuan Cui Bo Zhang 《Astrophysics and Space Science》2006,306(1-2):33-39
The supernova yields of r-process elements are obtained as a function of the mass of their progenitor stars from the abundance patterns of extremely metal-poor stars on the left-side [{Ba/Mg}]--[{Mg/H}] boundary with a procedure proposed by Tsujimoto and Shigeyama. The ejected masses of r-process elements associated with stars of progenitor mass M
ms ≤ 18 M
⊙ are infertile sources and the SNe II with 20 M
⊙ ≤ M
ms ≤ 40 M
⊙ are the dominant source of r-process nucleosynthesis in the Galaxy. The ratio of these stars 20 M
⊙ ≤ M
ms ≤ 40 M
⊙
with compared to the all massive stars is about∼ 18%. In this paper, we present a simple model that describes a star's [r/Fe] in terms of the nucleosynthesis yields of r-process elements and the number of SN II explosions. Combined the r-process yields obtained by our procedure with the scatter model of the Galactic halo, the observed abundance patterns of the metal-poor stars can be well reproduced. 相似文献
15.
Takuji Tsujimoto Toshikazu Shigeyama Yuzuru Yoshii 《Astrophysics and Space Science》2002,281(1-2):221-222
Following our hypothesis that each supernova (SN) event triggers star formation in the swept-up gas, so that newly formed
stars inherit the elemental abundance pattern of individual SNe, we deduce the production sites and yields for r-process elements. We further show that a strong evidence for the origin of r-process nucleosynthesis products was just there in our backyard - supernova SN1987A -, and conclude that 20 M
⊙ SNe are the predominant production sites for r-process elements.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
16.
We study the nucleosynthesis and the induced mixing during the merging of massive stars inside a common envelope. The systems
of interest are close binaries, initially consisting of a massive red supergiant and a main-sequence companion of a few solar
masses. We apply parameterized results based on hydrodynamical simulations to model the stream-core interaction and the response
of the star in a standard stellar-evolution code. Preliminary results are presented illustrating the possibility of unusual
nucleosynthesis and post-merging dredge-up which can cause composition anomalies in the supergiant's envelope.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
17.
《New Astronomy Reviews》2002,46(8-10):541-545
We examine the isotope production in star forming regions through a model of stellar-group population synthesis evolution. From this we obtain the light-curves of γ-ray line emission due to radioactive decay of 26Al, 60Fe and the e−e+ annihilation line. We discuss in particular, the effects of the dispersion due to the discreteness of the stellar populations. We conclude that when predicted γ-ray line observations are combined with other multi-wavelength measurements, one can efficiently constrain the age of a stellar population, and help to identify the primary nucleosynthesis sources of the radio-isotopes. 相似文献
18.
A. G. W. Cameron 《Astrophysics and Space Science》1982,82(1):123-131
An effort has been made to determine the contributions of the S- and R-processes of nucleosynthesis to the abundances of the heavy element isotopes. It has been concluded that the general previous assumption concerning the exclusive assignment of isobars to one or the other of these processes is probably in error. The R-process abundances are characterized by relatively small fluctuations in the abundances of odd and even mass numbers. If this is always true, and such is assumed here, then there are substantial S-process contributions to the abundances of R-process isobars. This is consistent with transient flashing episodes in the S-process neutron production processes. The primary tool for the separation of the abundances due to the two processes therefore had to be achievement of a reasonably smooth and monotonically-decreasing curve of the abundance of the S-process yields times the neutron capture cross-sections versus mass number. Tables of the separate yields are given. 相似文献
19.
I. S. Shklovskii 《Journal of Astrophysics and Astronomy》1984,5(1):13-18
It is argued that the iron nucleosynthesis rate in the universe due to SNI outbursts is dependent on the mass function of
star formation. Since the mass function depends on the chemical composition and since the masses of SNI precursors have upper
limits, the iron nucleosynthesis rate was low at an earlier evolutionary epoch of the universe when mainly massive stars were
formed. The iron nucleosynthesis rate should reach a maximum near z ∼ 0.5. At such or similar value of z the well-known ‘step’
in the cosmic γ-ray background spectrum may be explained by the presence of γ-gray quanta accompanying the radioactive56Co →56Fe decay. An argument is presented against the identification of the hidden mass of the universe with black-hole remnants
of ‘type III’ stars. 相似文献
20.
Ravi Subrahmanyan 《Journal of Astrophysics and Astronomy》1997,18(4):251-255
The discovery of the 3K microwave background radiation (MBR) and its interpretation as a relict of the hot big bang was probably the most important
observation that led to the elevation of the hot big bang model to the status of a ‘Standard Model’. The temperature of this
background is consistent with the primordial nucleosynthesis hypothesis. Detailed measurements of the spectrum and angular
anisotropy of this radiation background have been found — within the measurement errors - to be consistent with the expectations
of the Standard Model and with the formation of structure from the gravitational growth of primordial seed density perturbations
within this framework. 相似文献