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Light and cold extrasolar planets such as OGLE 2005‐BLG‐390Lb, a 5.5 Earth masses planet detected via microlensing, could be frequent in the Galaxy according to some preliminary results from microlensing experiments. These planets can be frozen rocky‐ or ocean‐planet, situated beyond the snow line and, therefore, beyond the habitable zone of their system. They can nonetheless host a layer of liquid water, heated by radiogenic energy, underneath an ice shell surface for billions of years, before freezing completely. These results suggest that oceans under ice, like those suspected to be present on icy moons in the Solar system, could be a common feature of cold low‐mass extrasolar planets. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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We investigate the effect of microlensing on parameters of the images of distant sources seen near the critical curves of complex gravitational lenses, which are represented as a sum of compact structures—microlenses (stars, star-like or planet-like bodies) and diffusely distributed matter (dust and gas clouds etc.). The observation of merging, cross-shaped, annular, or arc-shaped source images is an indication that the images are close to the critical curves of gravitational lenses. Our analysis and numerical solution have allowed us to determine the structures of the critical curves and caustics formed by macro-and microlenses, as well as to estimate the characteristic perturbations introduced by microlenses at their various positions relative to the critical curve of a regular gravitational lens. We show that, the closer are the microlenses to the critical curve, the larger is the discrepancy between our results and those obtained previously with standard (linearized) allowance for the effect of a regular gravitational lens. 相似文献
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该文综述了利用微引力透镜效应来搜寻银河系内重子暗物质的原理、观测方法和结果以及当前国际上几个小组的工作和主要进展。简要回顾了对重子暗物质的认识过程，其中广泛分布于星系之中的暗天体被称为晕族大质量致密天体（MACHO）。综述了一些关于引力透镜的一些基本概念和基本公式，其中简单讨论了强引力透镜、弱引力透镜和微引力透镜的区别，并列出微引力透镜的两个重要参数光深和光变时标的定义及表达式。详细阐述了对于MACHO探测的方法和一些观测效应细节。综述了目前几个小组的工作，包括MACHO小组和EROS小组等，其中MACHO小组近来的工作得出MACHO为银晕的重要组成部分，其质量比例约为20％；而EROS最近工作得出的质量比例上限为7％。 相似文献
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The effect of weak gravitational microlensing on the pulsar timing is considered. The residuals of the times of arrival due to this effect for the pulsar B1937+21 will be ～10 ns if the time span of observations is about 20 years. It has also been shown that the residuals due to this effect will be several microseconds in the same 20 years in future SKA (Square Kilometer Array) observations of pulsars located behind the bulge. 相似文献
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We consider the motion of the image of a distant radiation source microlensed by one and many point masses in the presence of an external background field, which produces a shear in the lens equation. The trajectories of the image brightness centroid (BC) in a Chang-Refsdal lens are very sensitive to the magnitude of the shear and to the direction of motion of the microlenses, allowing these parameters to be unambiguously determined from the BC motion. Stochastic motions of the BC for an extended source are simulated in a problem with a large number of randomly arranged microlenses. We derive dependences of the root-mean-square variations in BC velocity on microlense density, on external shear, and on the continuous component of the mass density, which may be related to dark matter in extragalactic lenses. 相似文献
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简述了第二个天体测量卫星Gaia(将于2013年3月发射)项目的科学意义,并给出了该项目的组织工作和最近的进展.描述了Gala观测资料处理的基本原理,以及与依巴谷观测资料处理的不同点.介绍了Gaia参考架构建的考虑,以及为了构建微角秒量级的参考架,应在自行中加入系统差改正,如长期光行差、引力波效应、宇宙膨胀各向异性的影响,弱的微引力透镜和微引力透镜噪声效应等.介绍了Gaia光学参考架与射电参考架ICRFL2之间建立联系过程中,选择河外射电源的准则,其中包括源的核漂移和光学长期变化监测等.最后,提出了我国现有设备参与支持Gaia的地基观测,以及正在研制的65 m射电天线在射电天体测量方面可以开展的若干课题. 相似文献
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A. M. Cherepashchuk M. V. Sazhin I. A. Trifalenkov 《Astrophysics and Space Science》1995,229(2):265-299
The observation of microlensing events towards the Large Magellanic Cloud and Galactic Bulge discovers a new population of our Galaxy which is that of dark bodies with masses of the order of 0.1M
. Astronomy has now a unique ability: one can use the microlensing as a space telescope with extremely high angular resolution. Here we discuss the opportunity of the application of this ability to observation of close binaries. Stars in a binary system move around their barycenter and as a result the apparent motion is modulated by binary motion. The light curve of this microlensing event becomes nonsymmetrical. If a binary has two stars with different spectral types, one can expect significant variation of color during microlensing effect. Accurate light curves for some typical binaries have been calculated and are presented here. The total fraction of binaries in our Galaxy is around 50%. Therefore one can expect half of the microlensing events to have nonsymmetrical and wavelength depending light curves which would indicate that background star is binary. Our opinion is that the absence of these light curves are due to some selection effect. This leads to an underestimation of the density of the dark body population in our Galaxy by a factor of about two. 相似文献
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