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21.
U. Ott 《Journal of Earth System Science》1998,107(4):379-390
An overview is given of the identified surviving presolar grains in primitive meteorites. Two of these phases are discussed
in more detail: (a) Presolar silicon carbide, with special emphasis on heavy element isotopic compositions which trace the
slow neutron capture process (s-process) of nucleosynthesis. It is argued that there are problems either with the grain or
neutron capture cross section data or with current basic understanding of heavy element nucleosynthesis, (b) Presolar diamonds,
where new developments are discussed concerning the origin of the (supernova) Xenon-HL component thought to be contained within
them; in addition, arguments are presented in favor of diverse carrier phases for the various Xe components observed in diamond
separates. 相似文献
22.
Carlos Abia Jordi Isern & Ute Lisenfeld 《Monthly notices of the Royal Astronomical Society》1998,299(4):1007-1012
The observed Be and B relationships with metallicity clearly support the idea that both elements have a primary origin and that they are produced by the same class of objects. Spallation by particles accelerated during gravitational supernova events (SNII, SNIb/c) seems to be a likely origin. We show, in the context of a model of chemical evolution, that it is possible to solve the Li, Be and B abundance puzzle with the yields recently proposed by Ramaty et al., provided that SNII are unable to accelerate helium nuclei significantly and that different mechanisms are allowed to act simultaneously. 相似文献
23.
Richard J. Stancliffe Maria Lugaro Claudio Ugalde Christopher A. Tout Joachim Görres Michael Wiescher 《Monthly notices of the Royal Astronomical Society》2005,360(1):375-379
In the light of recent recalculations of the 19 F(α, p)22 Ne reaction rate, we present results of the expected yield of 19 F from Wolf–Rayet (WR) stars. In addition to using the recommended rate, we have computed models using the upper and lower limits for the rate, and hence we constrain the uncertainty in the yield with respect to this reaction. We find a yield of 3.1 × 10−4 M⊙ of 19 F with our recommended rate, and a difference of a factor of 2 between the yields computed with the upper and lower limits. In comparison with previous work we find a difference in the yield of a factor of approximately 4, connected with a different choice of mass loss. Model uncertainties must be carefully evaluated in order to obtain a reliable estimate of the yield, together with its uncertainties, of fluorine from WR stars. 相似文献
24.
E. M. Drobyshevski 《Monthly notices of the Royal Astronomical Society》2000,311(3):L1-L3
We start from the hypothesis that the dark matter of the Galactic disc contains Planckian particles carrying a negative electric charge of up to Z =10, which we call dark electric matter objects (daemons). Daemons are capable of catalysing proton-fusion reactions, which may account for the observed solar neutrino deficiency. The inevitable poisoning of the catalytic property of daemons as they capture heavy nuclei ( A 20) in the interior of the Sun is used to estimate the decay time of a daemon-containing nucleus (nucleon) in quantum-relativistic processes, which remain largely unknown. This time is τ ex ∼10−7 s. This may mean that the lower limit on the mass of an intranucleonic particle interacting with a daemon is ∼108 –1010 GeV and, possibly, even ∼1014 –1015 GeV. The desirability of a search for multiple events occurring with an interval ∼ τ ex along the 'slow' daemon trajectories on operating installations dedicated to detection of the proton decay is pointed out. 相似文献
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26.
Anne Decourchelle 《Astrophysics and Space Science》2002,281(1-2):271-274
Supernovae and their remnants play an essential role in the Interstellar Medium as one of the main sources of mechanical energy
and heavy element production and as cosmic-ray accelerators. X-ray spectro-imagery is a key approach to look at these issues,
as the collision of high velocity ejecta with the ambient medium generates high temperatures of the order of ten million degrees.
I present recent results from the XMM-Newton and Chandra X-ray satellites on the elemental composition of young supernova
remnants, on the spatial distribution of these synthesized elements and on the constraints obtained on the efficiency of particle
acceleration at the shocks.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
27.
Greg Ushomirsky Robert E. Rutledge 《Monthly notices of the Royal Astronomical Society》2001,325(3):1157-1166
Transiently accreting neutron stars in quiescence ( L X ≲1034 erg s−1 ) have been observed to vary in intensity by factors of few, over time-scales of days to years. If the quiescent luminosity is powered by a hot neutron star core, the core cooling time-scale is much longer than the recurrence time, and cannot explain the observed, more rapid variability. However, the non-equilibrium reactions which occur in the crust during outbursts deposit energy in isodensity shells, from which the thermal diffusion time-scale to the photosphere is days to years. The predicted magnitude of variability is too low to explain the observed variability unless – as is widely believed – the neutrons beyond the neutron-drip density are superfluid. Even then, the variability due to this mechanism in models with standard core neutrino cooling processes is less than 50 per cent – still too low to explain the reported variability. However, models with rapid core neutrino cooling can produce a variability by a factor as great as 20, on time-scales of days to years following an outburst. Thus, the factors of ∼ few intensity variability observed from transiently accreting neutron stars can be accounted for by this mechanism only if rapid core cooling processes are active. 相似文献
28.
High signal-to-noise ratio spectra were obtained of 10 high-proper-motion stars having −1 ≲[Fe/H] < 0 , and a comparable number of disc stars. All but two of the high-proper-motion stars were confirmed to have [Fe/H] > −1.0 , some approaching solar metallicity, but, even so, earlier measurements overestimated the metallicities and velocities of some of these stars. Models of stellar populations were used to assign membership probabilities to the Galactic components to which the high-velocity stars might belong. Many were found to be more probably thick-disc than halo objects, despite their large space motions, and two might be associated with the inner Galaxy. It may be necessary to reassess contamination of previous halo samples, such as those used to define the metallicity distribution, to account for contamination by high-velocity thick-disc stars, and to consider possible subcomponents of the halo.
The change in [α/Fe] ratios at [Fe/H]≃−1.0 is often used to constrain the degree and timing of Type Ia supernova nucleosynthesis in Galactic chemical-evolution models. [Ti/Fe] values were measured for eight of the high-velocity stars. Both high- and low-[Ti/Fe] halo stars exist; likewise high- and low-[Ti/Fe] thick-disc stars exist. We conclude that the [Ti/Fe]'break' is not well defined for a given population; nor is there a simple, continuous evolutionary sequence through the break. Implications for the interpretation of the [α/Fe] break in terms of SN Ia time-scales and progenitors are discussed. The range of [Ti/Fe] found for high -velocity (low rotation) thick-disc stars contrasts with that for the low -velocity (high rotation) thick-disc sample studied by Prochaska et al. 相似文献
The change in [α/Fe] ratios at [Fe/H]≃−1.0 is often used to constrain the degree and timing of Type Ia supernova nucleosynthesis in Galactic chemical-evolution models. [Ti/Fe] values were measured for eight of the high-velocity stars. Both high- and low-[Ti/Fe] halo stars exist; likewise high- and low-[Ti/Fe] thick-disc stars exist. We conclude that the [Ti/Fe]'break' is not well defined for a given population; nor is there a simple, continuous evolutionary sequence through the break. Implications for the interpretation of the [α/Fe] break in terms of SN Ia time-scales and progenitors are discussed. The range of [Ti/Fe] found for high -velocity (low rotation) thick-disc stars contrasts with that for the low -velocity (high rotation) thick-disc sample studied by Prochaska et al. 相似文献
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恒星尘埃的实验室研究--实验天体物理学 总被引：1，自引：0，他引：1
原始球粒陨石含有来自恒星的微小固体颗粒(微米级),这些尘埃的同位素组成与太阳系物质截然不同,它们是目前唯一能直接获得的恒星固体样品．已发现的恒星尘埃有金刚石、石墨、碳化硅、刚玉、尖晶石、氮化物、和硅酸盐等,它们的母体恒星包括红巨星,AGB恒星、新星和超新星．对恒星尘埃的研究,使得更深入地了解星系的化学演化历史、恒星内部的核反应和湍流机制、恒星大气中尘埃的形成、星际介质物理现象等．恒星尘埃把天体物理领域延伸到了微观世界,它有机地结合了地球化学实验技术和天体物理理论,开辟了一门崭新的天文学分支实验天体物理学． 相似文献