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31.
Hans Zinnecker 《Astrophysics and Space Science》2002,281(1-2):147-157
In this brief report we summarise the most important points raised in the course of a two-hour evening discussion session
on the above topic, organised by the author. Major questions that were debated included the universality of the IMF, the history
of the star formation rate in the solar neighorhood, the star formation efficiency in molecular clouds, and the role of triggered
star formation. The issue of a threshold gas surface density for star formation to occur was also critically discussed.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
32.
在Li&Yang (2 0 0 1 )所给出的局部对流理论的基础上 ,我们进一步采用梯度型方案给出了非局部对流理论 ,并将它用于太阳模型中。这一理论考虑了恒星对流区内的非局部效应 ,它得到了一个与原来用混合长理论或局部理论给出的结果有所区别的对流区 ,扩散效应很明显。但是 ,目前我们的理论还不能处理时间相关的对流以及对流超射等问题。这些问题将在后续工作中加以考虑。当把这一理论应用于太阳模型中时 ,我们发现它对标准太阳模型的改正非常微小。我们讨论了这一现象 ,并对其加以解释 相似文献
33.
对疏散星团进行统计研究时,场星的混淆可能是一个严重问题,必须认真对待。本文详细讨论了在估算疏散星团维里(Virial)质量时,正确利用成员概率的重要性。分析表明,只有利用大概率的成员星才能得到合理的星团Virial质量。重新计算后M11的Virial质量为5094μ_⊙,与直接观测到的光度质量的最新结果(4671μ_⊙)符合得很好,维里系数为0.9。 相似文献
34.
The fast neutron capture process (the r-process) occurs in the neutron-rich circumstance. However its concrete physical environment is not very clear. With recent progress in observations, many extremely metal-poor halo stars have been discovered. They have two characteristics: one is the overabundance of fast neutron elements with the relative abundance consistent with that of the sun; the other is that fast neutron element contents in stars at the same metal abundance have a very large dispersion. This provides a particular way to study the origin of the r-process. Simulation was used to study the galaxy's evolution process and the resulting dispersion of fast neutron nuclide contents in stars. The model of galaxy evolution obtained in this way not only contains spontaneous star formation in the gas region, but also includes the star formation excited by the supernova explosion. It is shown from our results that the supernovae at the low mass end should be the place producing the fast neutron nuclides. In addition, it is also shown that the non-uniformity of the galaxy evolution caused by the supernova explosion is not enough to explain the observed dispersion of fast neutron element contents in halo stars. This problem should be further studied. 相似文献
35.
Xue-Bing Wu Wen-Wen Zuo Qian Yang Wei-Min Yi Chen-Wei Yang Wen-Juan Liu Peng Jiang Xin-Wen Shu and Hong-Yan Zhou 《天文和天体物理学研究(英文版)》2012,(9):1185-1190
Quasars with redshifts greater than 4 are rare, and can be used to probe the structure and evolution of the early universe. Here we report the discovery of six new quasars with i-band magnitudes brighter than 19.5 and redshifts between 2.4 and 4.6 from spectroscopy with the Yunnan Faint Object Spectrograph and Camera (YFOSC) at the Lijiang 2.4 m telescope in February, 2012. These quasars are in the list of z > 3.6 quasar candidates selected by using our proposed J K/i Y criterion and the photometric redshift estimations from the SDSS optical and UKIDSS near-IR photometric data. Nine candidates were observed by YFOSC, and five among six new quasars were identified as z > 3.6 quasars. One of the other three objects was identified as a star and the other two were unidentified due to the lower signal-to-noise ratio of their spectra. This is the first time that z > 4 quasars have been discovered using a telescope in China. Thanks to the Chinese Telescope Access Program (TAP), the redshift of 4.6 for one of these quasars was confirmed by the Multiple Mirror Telescope (MMT) Red Channel spectroscopy. The continuum and emission line properties of these six quasars, as well as their central black hole masses and Eddington ratios, were obtained. 相似文献
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Public concern about earthquakes linked to wastewater injection from fracking operations is rising. However, few have examined how “induced seismicity” is acted upon by state officials. For some, an incremental response to smaller quakes can be viewed as an acceptable risk policy orientation because of the sizeable economic benefits that accompany drilling activities while others prefer risk mitigation policies (such as the use of “threshold policies”) as a better way to address quake-related problems. To account for state response to induced seismicity impacts, we examine three factors: the emergence of quakes as focusing events, the economic importance of oil and gas to state jobs and revenue, and selected characteristics of earthquakes as a policy issue, i.e., complexity and categorical precedence. Using information drawn from documentary sources, we consider which factors are most helpful in accounting for agency decisions aimed at reducing seismic risks linked to nearby injection wells. 相似文献