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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
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Y. Fenner M. T. Murphy B. K. Gibson 《Monthly notices of the Royal Astronomical Society》2005,358(2):468-480
At redshifts z abs ≲ 2 , quasar absorption-line constraints on space–time variations in the fine-structure constant, α, rely on the comparison of Mg ii and Fe ii transition wavelengths. One potentially important uncertainty is the relative abundance of Mg isotopes in the absorbers, which, if different from solar, can cause spurious shifts in the measured wavelengths and, therefore, α. Here we explore chemical evolution models with enhanced populations of intermediate-mass (IM) stars, which, in their asymptotic giant branch phase, are thought to be the dominant factories for heavy Mg isotopes at the low metallicities typical of quasar absorption systems. By design, these models partially explain recent Keck/HIRES evidence for a smaller α in z abs < 2 absorption clouds than on Earth. However, such models also overproduce N, violating observed abundance trends in high- z abs damped Lyman-α (DLA) systems. Our results do not support the recent claim of Ashenfelter et al. that similar models of IM-enhanced initial mass functions (IMFs) may simultaneously explain the HIRES varying-α data and DLA N abundances. We explore the effect of the IM-enhanced model on Si, Al and P abundances, finding it to be much less pronounced than for N. We also show that the 13 C/12 C ratio, as measured in absorption systems, could constitute a future diagnostic of non-standard models of the high-redshift IMF. 相似文献
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Michael Mayer Wolfgang J. Duschl 《Monthly notices of the Royal Astronomical Society》2005,358(2):614-631
We present newly calculated low-temperature opacities for gas with a primordial chemical composition. In contrast to earlier calculations, which took a pure metal-free hydrogen/helium mixture, we take into account the small fractions of deuterium and lithium as resulting from standard big bang nucleosynthesis. Our opacity tables cover the density range −16 < log ρ[g cm−3 ] < −2 and the temperature range of 1.8 < log T [K] < 4.6 , while previous tables have usually been restricted to T > 103 K . We find that, while the presence of deuterium does not significantly alter the opacity values, the presence of lithium gives rise to major modifications of the opacities, at some points increasing it by approximately two orders of magnitude relative to pure hydrogen/helium opacities. 相似文献
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利用核的壳层模型，讨论了电荷屏蔽对超新星的前身星阶段一些较丰的核在一些重要的温度－密度点的电子俘获率的影响，结果表明由于电荷屏蔽的作用基电子丰度变化率下降了10－20％。 相似文献
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D. G. Yakovlev L. Gasques M. Wiescher 《Monthly notices of the Royal Astronomical Society》2006,371(3):1322-1326
We study the pycnonuclear burning of 34 Ne in the inner crust of an accreting neutron star. We show that the associated energy production rate can be calculated analytically for any arbitrary temporal variability of the mass accretion rate. We argue that the theoretical time-scale for 34 Ne burning is currently very uncertain and ranges from a fraction of a millisecond to a few years. The fastest allowable burning may change the composition of the accreted crust while the slowest burning leads to a time-independent nuclear energy generation rate for a variable accretion. The results are important for constructing self-consistent models of the accreted crust and deep crustal heating in neutron stars which enter soft X-ray transients. 相似文献
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