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41.
Johan Holmberg Birgitta NordstrÖm Bjarne Rosenkilde Jørgensen Johannes Andersen 《Astrophysics and Space Science》2003,284(2):685-688
The evolution of the Solar neighbourhood is followed using a unique, magnitude complete and kinematically unbiased sample
of 14,000 F, G, and K dwarfs. Metallicity, age, space motion and galactic orbits have been determined for all stars. The result
is a detailed view of the complex evolution of the local Milky Way, which must be matched by any model for the chemical and
dynamical evolution of the Galactic disk. E.g., such models must explain the shape and large scatter in the age-metallity
relation as well as the overall metallicity distribution; the evolution of stellar kinematics with age; the distribution of
stars in velocity space; and the contributions from the thick and thin disks to all these relations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
42.
Stefan J. Wijnholds A. Ger De Bruyn Jaap D. Bregman Jan Geralt Bij De Vaate 《Experimental Astronomy》2004,17(1-3):59-64
The thousand element array (THEA) system is a phased array system consisting of 1 m2 tiles having 64 Vivaldi elements each, arranged on a regular 8-by-8 grid, which has been developed as a demonstrator of technology and applicability for SKA. In this paper we present imaging results of Galactic neutral hydrogen with THEA. Measurements have been taken using a dense 2-by-2 array of four tiles as a four tile adder. The results are compared with results from the Leiden-Dwingeloo Survey, showing qualitative agreement, but also indicating that further studies are needed on the instrumental characteristics. 相似文献
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Marc Fouchard Christiane Froeschlé Giovanni Valsecchi Hans Rickman 《Celestial Mechanics and Dynamical Astronomy》2006,95(1-4):299-326
We introduce a model for integrating the effects of Galactic tides on Oort cloud comets, which involves two procedures, according to the values of the osculating semi-major axis a and eccentricity e. Ten simulations of the dynamics of 106 comets over 5 Gyr are performed using this model. We thus investigate the long-term effects of the Galactic tide with and without a radial component, the effects of the local density of the Galactic disk, and those of the Oort constants. Most of the results may be understood in terms of the integrability or non-integrability of the system. For an integrable system, which occurs for moderate semi-major axes with or without radial component, the dynamics is explained by periodic variation of the cometary perihelion, inducing the depletion of the outer region of the Oort cloud, a constant flux from the inner region after 500 Myr, and the quick formation of a reservoir of comets with argument of perihelion near 26.6°. When the system is non-integrable, the efficiency of the tide in reducing the cometary perihelion distance is enhanced both by replenishing the Oort cloud domain from which comets are sent toward the planetary system, and by reducing the minimal value that the perihelion distance may reach. No effects of varying the Oort constants were observed, showing that the flat rotation curve is a satisfactory approximation in Oort cloud dynamics. 相似文献
46.
多目标的地质大调查 ——21世纪勘查地球化学的战略选择 总被引：12，自引：0，他引：12
21世纪勘查地球化学面临发展问题.2001～2005年勘查地球化学以国家其基础性公益性地质工作为主导,以经济社会发展需求为动力,以资源与环境并重为方针,实施多目标的地质大调查,取得一系列重要成果,标志勘查地球化学进入全面发展阶段.这是勘查地球化学的战略选择.在现代科学技术取得最新成就起点上,构建理论体系、方法体系和质量体系,在各项工作中采取科学态度和积极有效措施,推动勘查地球化学不断达到新的高度. 相似文献
47.
We studied the particle growth in a protoplanetary disk in a high-ionization environment and found that icy planet formation is inactive for a disk with an ionization rate 100 times higher than that of the present Solar System. In particular, in the case of M 10~(-7.4)M_☉yr~(-1), only rocky planet formation occurs. In such a case, all the solid materials in the disk drift inward, eventually reach the inner MRI front,and accumulate there. They form a dense, thin sub-disk of solid particles, which undergoes gravitational instability to form rocky planetesimals. The planetesimals rapidly grow into a planet through pebble accretion. Consequently, rocky planets tend to be much larger than planets formed through other regimes(tandem planet formation regime and dispersed planet formation regime), in which icy planet formation actively takes place. These rocky planets may evolve into hot Jupiters if they grow fast enough to the critical core mass of the runaway gas accretion before the dispersal of the disk gas, or they may evolve into super-Earths if the gas dispersed sufficiently early. 相似文献
48.
中国地质科学院所属的地质研究所、矿产资源研究所、地质力学研究所、水文地质环境地质研究所、岩溶地质研究所、地球物理地球化学勘查研究所及院机关在对其2013年度承担的总计1022个科技项目进行所级选拔择优的基础上, 于2014年1月9—10日在北京召开了中国地质科学院2013年度科技成果汇报交流暨十大科技进展评选会, 对推荐出的21项优秀科技成果进行汇报交流。来自国土资源部、教育部、中国科学院、中国地震局、中国石油化工集团公司等部门的42位院士专家组成的评选委员会, 经过认真、严谨的评审和投票, 评选出了中国地质科学院2013年度十大科技进展并逐一进行了点评。获奖成果涉及学科领域包括基础地质、矿产资源、水文地质工程地质与环境地质和技术方法, 代表了中国地质科学院的最新、最高研究水平。 相似文献
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获得完备的样本一直是类星体统计分析工作中至关重要的第一步。类星体巡天选择候选体的方法主要有射电波段筛选、色指数筛选、无缝光谱筛选、X射线波段筛选、对红外源或变源进行筛选和零自行的方法。单独运用任一方法都有选择效应,采用多波段方法可以极大地提高样本的完备性。阐述了使用多波段方法选择活动星系核样本的研究现状,提出多波段类星体巡天方法和选源判据,给出ROSAT巡天中F.1002,F.Coma,F.836和F.Leo 4个天区以及空源的15年来X射线选活动星系核的选源和光学新证认的AGN结果,表明多波段类星体巡天方法能有效地提高观测效率。 相似文献