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1.
“星系对”研究的飞速进展,得益于光谱红移巡天和多波段图像观测。选择的星系对数目不断增多,数据准确度和完备性不断提高,促进了与星系对相关的课题研究。首先介绍了星系对的选择情况,包括目前已选择的星系对数目和选择判据在实际应用过程中的改进和发展情况;讨论了数据的完备性对星系对选择和研究的影响,不同波段星系对选择的优缺点;其次概述了目前在星系对方面的研究课题;最后是对星系对研究的展望。 相似文献
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本文在前文[1]研究的基础上对判断分光双星自转的同步性在理论上做了进一步改进.对双谱分光双星用视向速度曲线的半振幅K_1和K_2代替质量比q.对单谱分光双星除前文给出一种判断同步性方法外又给出两种方法.另外,用改进的公式对6对分光双星的同步性做了计算和判断.最后对所得结果做了讨论并用结束语对此项研究工作做了回顾和展望. 相似文献
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对地球低轨道卫星 (LEO)轨道设计中的摄动力模型进行了分析 ,并估计了其量级。然后针对用于GPS无线电掩星的LEO卫星轨道设计对掩星地面测点稳定性的要求 ,对力学模型进行了取舍 ,同时估计了各摄动力模型对轨道设计目标的影响 相似文献
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LEO卫星轨道设计中的主要摄动源影响评估 总被引：3，自引：0，他引：3
对地球低轨道卫星（LEO）轨道设计中的摄动力模型进行了分析，并估计了其量级。然后针对用于GPS无线电掩星的LEO卫星轨道设计对掩星地面测点稳定性的要求，对力学模型进行了取舍，同时估计了各摄动力模型对轨道设计目标的影响。 相似文献
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针对FAST的天文观测要求,对其天文观测软件进行了设计与开发。首先介绍了FAST天文观测的原理,对天文观测软件进行了需求分析。而后提出了馈源天文运动轨迹规划算法,并进行了仿真。针对其轨迹要求给出了控制方法,对天文观测控制软件进行了设计与实现。最后通过现场实地实验,验证了本文所提的算法与软件的可行性。 相似文献
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首先回顾了火星重力场探测的历史、各有关探测器的轨道特征和获取的资料情况,特别对最成功的MGS项目的情况作了详细介绍。然后对确定火星重力场模型过程中的有关问题作了介绍,包括动力学模型、三体摄动问题、太阳光压和大气阻力模型等。重点介绍了其中的先验条件和求解重力场的算法,后者主要介绍GSFC采用的最小二乘法和先验约束方法及其数据定权和误差校准的经验。文中还对火星重力场与地形学进行了比较分析,并对火星重力场时变性的探测与研究作了重点讨论。最后对火星重力场探测中存在的主要问题作了详细讨论,并展望了我国第一颗火星探测器"萤火一号"对火星重力场研究的可能贡献。 相似文献
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讨论了激光测距仪测距本领的限制因素,找出了诸多限制因素的内在联系,得出了影响测距能力的关键因素是目标的照明概率.在前人已有的对激光测距仪最佳发散角的选取方法基础上,对其进行了改进.新得到的方法在选取最佳发散角时具有快速、简洁和精确度高等特点,并利用多项式拟合对其进行了简化,使其可用于粗略估算.最后,利用数值模拟对新方法进行了验证分析. 相似文献
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Manabu Yuasa 《Celestial Mechanics and Dynamical Astronomy》1992,54(1-3):291-293
The asteroids whose perihelion distances (q) are smaller than 0.983 AU and aphelion distances (% MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiqadgfagaqeaaaa!3D1C!\[\bar Q\]) are larger than 1.017 AU are called Apollo type objects. Similarly Amor type objects are defined by the conditions: 0.987 AU < % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiqadghagaqeaaaa!3D3C!\[\bar q\] < 1.382 AU and % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiqadgfagaqeaaaa!3D1C!\[\bar Q\] > 1.666 AU. Both types are peculiar asteroids and have common dynamical behaviors. So, we regard these two type asteroids as one group and try to search for families among them. 相似文献
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Properties, including the time duration, polarization, quasi-periodical oscillations and so on, of the microwave spike emissions observed at 2.5 GHz and 2.6 GHz during the solar flare of 1991 May 16 are analyzed statistically. The left-handed and right-handed circular polarizations of the spike emissions at 2.5, 2.6 and 3.1 GHz are reported in detail. At these 3 frequencies, most of the spikes are superposed on both the rising (and maximum) and the descending phase of the burst. It is noteworthy that spikes also appeared superposed on the small bursts that appeared after the main burst. The spike emission lasted 17 minutes. Polarization reversals on different timescales appearing in the spike emissions at 2.5 and 2.6 GHZ are described. Our statistical analysis indicates that the polarization reversals at 2.5 and 2.6 GHz differ in characters on average, the polarization reversal at 2.5 GHz is earlier than that of 2.6 GHz by about 1.5 minutes, and polarization reversal of the spike emission is more frequent at 2.5 GHZ. 相似文献
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Zamri Zainal Abidin Zainol Abidin IbrahimZulfazli Rosli Siti Fatin Fathinah MalimNorsuzian Mohd Anim Noorkhallaf Noorazlan 《New Astronomy》2012,17(2):61-64
In this paper, we investigated the radio frequency interference (RFI) that future Very Long Baseline Interferometer (VLBI) observations in Malaysia may encounter. Four frequency windows below 2.8 GHz were chosen for this study and their spectra were measured at four sites. The frequency windows are 322-328 MHz, 608-614 MHz, 1660-1660.5 MHz and 1660.5-1668.4 MHz. The measured averaged RFI floor noise levels in these windows are −99.992 (±0.570) dBm, −99.907 (±0.639) dBm, −100.220 (±0.4941) dBm and −100.359 (±0.110) dBm, respectively. We found that only two bands below 2.8 GHz are permitted for the purpose of radio astronomy in Malaysia. They are 608-614 MHz and 1660-1660.5 MHz. The RFI levels in these permissible bands at the best site (Langkawi) were also measured and concluded to be relatively low. Main sources of RFI in these bands in Malaysia were identified. We also reviewed several current VLBI observations in these two bands. 相似文献
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Thomas E. Corbin 《Celestial Mechanics and Dynamical Astronomy》1980,22(1):25-34
Systematic reductions of nineteenth century observations to the system of the FK4 are discussed. Reductions made on a nightly basis are described and compared with the results obtained through the use of conventional tables. The series of observations made at the Paris Observatory from 1837 to 1881 was used to compare the two methods, and a combined system of 24 000 FK4, FK4 Sup and AGK 3R positions and proper motions provided the reference stars. The results show that for Uranus the mean error of a single observation in right ascension is ±1..33 when tables are used for the reductions, and ±1.12 when nightly reductions are made, while in declination the corresponding mean errors are ±0.88 and ±0.80. The observations of Neptune show an even greater difference between the two methods; the mean errors for the tabular and nightly reductions are ±1.57 and ±1.09 in right ascension and ±0.88 and ±0.75 in declination. Secular rates in the (0–C)'s of Uranus of –0.029/year in right ascension and ±0.030/year in declination are present when the observations are reduced with tables. These rates are reduced to –0.007/year and +0.015/year, respectively, when nightly reductions are made.Presented at the Symposium Star Catalogues, Positional Astronomy and Celestial Mechanics, held in honor of Paul Herget at the U.S. Naval Observatory, Washington, November 30, 1978. 相似文献
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Robert F. Howard 《Solar physics》1991,135(2):327-337
Digitized Mount Wilson sunspot data from 1917 to 1985 are analyzed to examine meridional motion and rotation properties as a function of latitude and distance () from the average latitude of activity (0) in each hemisphere. Latitude dependence similar to previous results is found, but only for spot groups whose areas are decreasing from one day to the next. A previous study of active region magnetic fields, using this technique of motions as a function of the average latitude of activity, had shown meridional motions on average toward 0. In this analysis of spot data some evidence is seen for motion away from 0, with some slight evidence for faster rotation equatorward of 0 and slower motion poleward of 0, similar to the torsional oscillation phenomenon. For reasons that are not clear, both of these effects are significantly more pronounced for sunspot groups whose areas are decreasing.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation. 相似文献
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Nonlinear propagation of strong low-frequency waves, as emitted by pulsars or compact galactic nuclei at their rotation frequencies, in a magnetized plasma is investigated. It is shown that even rather small amplitude waves can drive electrons to ultrarelativistic energies. In the limit when the electrons are ultrarelativistic but the ions are immobile, two types of circularly polarized waves (i.e., ± modes) are excited. In the wave zone of the Crab pulsar, both the electric field ( 3 V m–1) and the wavelength (108 m) of the - mode are larger, by an order of magnitude, than those of the + wave mode. Both ± modes can become modulationally unstable due to their nonlinear interaction with density fluctuations induced by the electrostatic waves. 相似文献
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A new model for the aggregation of cometesimals in the primordial solar nebula is proposed. The simulation of the aggregation takes into account disruptive and sticking effects of impacts on the aggregates properties together with the temporal evolution of cohesive strength during accretion due to sintering processes. Different regimes of aggregation are obtained depending on the value of the homogeneity exponent, μ, that indicates the fraction of kinetic energy available for cohesive energy dissipation during an impact. Porous fractal aggregates with different cohesive strength blocks are formed for 0 < μ < 0.4, while they are compact with a layered structure of different strengths for 0.4 < μ < 0.6 and weak ‘rubble piles’ for 0.6 < μ < 1. Cohesive strength estimations of the final cometary nuclei obtained give values generally lower than 10 kPa. The layered aggregates present the highest global cohesive strength, increasing their probability to survive collisions or moderate tidal stress. These results compare well with the structural and cohesive properties of comets deduced from observations and laboratory simulations. 相似文献
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We have obtained spatially resolved spectra of Titan in the near-infrared J, H and K bands at a resolving power of ∼5000 using the near-infrared integral field spectrometer (NIFS) on the Gemini North 8 m telescope. Using recent data from the Cassini/Huygens mission on the atmospheric composition and surface and aerosol properties, we develop a multiple-scattering radiative transfer model for the Titan atmosphere. The Titan spectrum at these wavelengths is dominated by absorption due to methane with a series of strong absorption band systems separated by window regions where the surface of Titan can be seen. We use a line-by-line approach to derive the methane absorption coefficients. The methane spectrum is only accurately represented in standard line lists down to ∼2.1 μm. However, by making use of recent laboratory data and modeling of the methane spectrum we are able to construct a new line list that can be used down to 1.3 μm. The new line list allows us to generate spectra that are a good match to the observations at all wavelengths longer than 1.3 μm and allow us to model regions, such as the 1.55 μm window that could not be studied usefully with previous line lists such as HITRAN 2008. We point out the importance of the far-wing line shape of strong methane lines in determining the shape of the methane windows. Line shapes with Lorentzian, and sub-Lorentzian regions are needed to match the shape of the windows, but different shape parameters are needed for the 1.55 μm and 2 μm windows. After the methane lines are modeled our observations are sensitive to additional absorptions, and we use the data in the 1.55 μm region to determine a D/H ratio of 1.77 ± 0.20 × 10−4, and a CO mixing ratio of 50 ± 11 ppmv. In the 2 μm window we detect absorption features that can be identified with the ν5 + 3ν6 and 2ν3 + 2ν6 bands of CH3D. 相似文献
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In situ (mobile) sampling of 33 natural dust devil vortices reveals very high total suspended particle (TSP) mean values of 296 mg m−3 and fine dust loadings (PM10) mean values ranging from 15.1 to 43.8 mg m−3 (milligrams per cubic meter). Concurrent three-dimensional wind profiles show mean tangential rotation of 12.3 m s−1 and vertical uplift of 2.7 m s−1 driving mean vertical TSP flux of 1689 mg m−3 s−1 and fine particle flux of ∼1.0 to ∼50 mg m−3 s−1. Peak PM10 dust loading and flux within the dust column are three times greater than mean values, suggesting previous estimates of dust devil flux might be too high. We find that deflation rates caused by dust devil erosion are ∼2.5-50 μm per year in dust devil active zones on Earth. Similar values are expected for Mars, and may be more significant there where competing erosional mechanisms are less likely. 相似文献
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