密云232MHz星表与6C星表的统计比较

我们对北京天台密云２３２ＭＨｚ星表和６Ｃ星表进行了系统的比较和研究，以期对密云星表的完备性和均匀性有一个定量的概念。     

密云232MHz星表的可靠性研究

利用密云综合孔径射电望远镜，在２３２ＭＨｚ频率，对于北纬３０°以上天区的巡天已经完成。除了银道面区域（│ｂ│〈１０°）的射电源外，密云总星表（ＭＧＣ）共包含了２６９５７颗射电源。ＭＧＣ的完整性和均匀性已在另讨论。本将利用所有处理完的ＭＳＲＴ资料和其它已发表的主要射电源表，研究密云总星表的可靠性。     

密云232MHz星表的可靠性研究(英文)

利用密云综合孔径射电望远镜，在232MHZ频率，对于北纬30°以上天区的巡天已经完成.除了银道面区域（|b|＜10°）的射电源外，密云总星表（MGC）共包含了26957颗射电源．MGC的完整性和均匀性已在另文讨论．本文将利用所有处理完的MSRT资料和其它已发表的主要射电源表，研究密云总星表的可靠性．     

FK5星表和依巴谷星表的比较

由ＦＫ５星表和依巴谷星表在不同历元上的比较、检测和讨论了ＦＫ５星表的系统差．结果表明，ＦＫ５星表的自行系统差可能是影响ＦＫ５星表位置系统差的主要来源．在一些研究工作中，例如在依巴谷星表系统中研究地球自转的长期变化或以前的照相观测结果的重新归算，需要考虑依巴谷星表自行个别误差的影响     

依巴谷星表和第谷星表的特征和意义

主要论述依巴谷星表和第谷星表的观测特征和天体测量特征,依巴谷卫星在短期内同时测定大量高精度的恒星位置,自行和视差等五个天体测量参数以及星等和色指数,依巴谷星表和第谷星表为建立高精度的光学参考系,为研究恒星的起源,演化,分布,质量,大小和光度等,为研究双星和聚星的分布和运动,为研究星系运动和星系动力学提供了大量的高精度资料,具有重要的科学意义。     

编制基本星表的方法简介

编制基本星表是用新的观测资料改进现有的基本星表系统。本文对编制基本星表的一般原理作了简述,并较为详细地介绍了系统改正时选取初始星表的方法,最后还介绍了确定每本初始星表相对权重的方法。     

天文星表入库的自动化

天文数据主要包括星表、星图、光谱、文献资料等,其中星表是包含天体信息的数据表格,是天文学家最常用到的天文数据。目前天文数据分布存储在全球各个数据中心。中国最大的天文数据中心是北京天文数据中心,其数据库的重要部分是天文星表数据库。本文阐述了建设天文星表数据库的意义,着重探讨了星表自动入库工具的实现,并介绍了在天文星表数据库基础上的数据融合和数据挖掘。     

天体测量星表与巡天观测的进展

该文简述了巡天观测和星表编制的历史和意义.介绍了天体测量星表与巡天观测的最新进展,如位置星表URAT、Pan-STARSS、LSST;自行星表LSPM、PM2000、BDKP;视差星表USNO,CTOPI、L和T型星的视差测定等.简略介绍了天体物理星表,其中包括测光星表GCPD、UBV、GSPC;光谱星表MSS、BDSS,SDSS和视向速度星表GCRV、CORALIE、RAVE.特别描述了恒星名至今仍在使用的20世纪初编制的Durchmusterung、Lowell、HenryDraper星表.描述了近年来普遍受到人们关注的联合星表编制的发展,如SKYMAP、距离太阳10 pc内的近距星表RECONS、描述了局部天区的HDF、双星星表等.另外还介绍了其他波段的巡天观测,如射电的NVSS、FIRST;近红外的IRAS PSC和FSS;X波段的WGCAT星表等.最后,对今后开展巡天观测和编制星表提出了应注意的几个问题.     

星表的系统误差和偶然误差

本文从星表系统误差和偶然误差的来源出发,叙述了初始星表和基本星表处理这些误差的方法,并着重介绍了确定系统差的数值图解法和分析法。     

中国古代星表数据的误差

对影响中国古代星表数据的各种误差进行了讨论。指出利用现代的数据处理方法剔除数据中的明显差错后，大部分系统误差可以通过现代的星表处理方法得到削弱，从而能对星表的精度水平有一个相对客观的了解。     

On the origin of the solar system and the exceptional position of the Sun in the Galaxy

The solar system's position in the Galaxy is an exclusive one, since the Sun is close to the corotation circle, which is the place where the angular velocity of the galactic differential rotation is equal to that of density waves displaying as spiral arms. Each galaxy contains only one corotation circle; therefore, it is an exceptional place. In the Galaxy, the deviation of the Sun from the corotation is very small — it is equal to ΔR/R _⊙≈0.03, where ΔR=R _c ?R _⊙,R _c is the corotation distance from the galactic center andR _⊙ is the Sun's distance from the galactic center. The special conditions of the Sun's position in the Galaxy explain the origin of the fundamental cosmogony timescalesT ₁≈4.6×10⁹ yr,T ₂?10⁸ yr,T ₃?10⁶ yr detected by the radioactive decay of various nuclides. The timescaleT ₁ (the solar system's ‘lifetime’) is the protosolar cloud lifetime in a space between the galactic spiral arms. The timescaleT ₂ is the presolar cloud lifetime in a spiral arm.T ₃ is a timescale of hydrodynamical processes of a cloud-wave interaction. The possibility of the natural explanation of the cosmogony timescales by the unified process (on condition that the Sun is near the state of corotation) can become an argument in favour of the fact that the nearness to the corotation is necessary for the formation of systems similar to the Solar system. If the special position of the Sun is not incidental, then the corotation circles of our Galaxy, as well as those of other galaxies, are just regions where situations similar to ours are likely to be found.     

Perturbations by the oblateness of the Earth and by the planets in the motion of the Moon

Perturbations in the motion of the Moon are computed for the effect by the oblateness of the Earth and for the indirect effect of planets. Based on Delaunay's analytical solution of the main problem, the computations are performed by a method of Fourier series operation. The effect of the oblateness of the Earth is obtained to the second order, partly adopting an analytical evaluation. Both in longitude and latitude are found a few terms whose coefficient differs from the current lunar ephemeris based on Brown's theory by about 0.01. While, concerning the indirect effect of planets, several periodic terms in the current ephemeris seem to have errors reaching 0.05.As for the secular variations of and due to the figure of the Earth and the indirect effect of planets, the newly-computed values agree within 1/cy with Brown's results reduced to the same values of the parameters. Further, the accelerations in the mean longitude, and caused by the secular changes in the eccentricity of the Earth's orbite and in the obliquity of the ecliptic are obtained. The comparison with Brown shows an agreement within 0.3/cy² for the former cause and 0.02/cy² for the latter. An error is found in the argument of the principal term for the perturbations due to the ecliptic motion in the current ephemeris.Proceedings of the Conference on Analytical Methods and Ephemerides: Theory and Observations of the Moon and Planets. Facultés universitaires Notre Dame de la Paix, Namur, Belgium, 28–31 July, 1980.     

On the model of the accumulation of the moon compatible with the data on the composition and the age of lunar rocks

It is suggested that the overall early melting of the lunar surface is not necessary for the explanation of facts and that the structure of highlands is more complicated than a solidified anorthositic ‘plot’. The early heating of the interior of the Moon up to 1000K is really needed for the subsequent thermal history with the maximum melting 3.5 × 10⁹ yr ago, to give the observed ages for mare basalts. This may be considered as an indication that the Moon during the accumulation retained a portion of its gravitational energy converted into heat, which may occur only at rapid processes. A rapid (t < 10³ yr) accretion of the Moon from the circumterrestrial swarm of small particles would give necessary temperature, but it is not compatible with the characteristic time 10⁸ yr of the replenishment of this swarm which is the same as the time-scale of the accumulation of the Earth. It is shown that there were conditions in the circumterrestial swarm for the formation at a first stage of a few large protomoons. Their number and position is evaluated from the simple formal laws of the growth of satellites in the vicinity of a planet. Such ‘systems’ of protomoons are compared with the observed multiple systems, and the conclusion is reached that there could have been not more than 2–3 large protomoons with the Earth. The tidal evolution of protomoon orbits was short not only for the present value of the tidal phase-lag but also for a considerably smaller value. The coalescence of protomoons into a single Moon had to occur before the formation of the observed relief on the Moon. If we accept the age 3.9 × 10⁹ yr for the excavation of the Imbrium basin and ascribe the latter to the impact of an Earth satellite, this collision had to be roughly at 30R, whereR is the radius of the Earth, because the Moon at that time had to be somewhere at this distance. Therefore, the protomoons had to be orbiting inside 20–25R, and their coalescence had to occur more than 4.0x10⁹ yr ago. The energy release at coalescence is equivalent to several hundred degrees and even 1000 K. The process is very rapid (of the order of one hour). Therefore, the model is valid for the initial conditions of the Moon.     

On the theory of the oblateness of the Sun

In this paper we first emphasize why it is important to know the successive zonal harmonics of the Sun's figure with high accuracy: mainly fundamental astrometry, helioseismology, planetary motions and relativistic effects. Then we briefly comment why the Sun appears oblate, going back to primitive definitions in order to underline some discrepancies in theories and to emphasize again the relevant hypotheses. We propose a new theoretical approach entirely based on an expansion in terms of Legendre's functions, including the differential rotation of the Sun at the surface. This permits linking the two first spherical harmonic coefficients (J ₂ and J ₄) with the geometric parameters that can be measured on the Sun (equatorial and polar radii). We emphasize the difficulties in inferring gravitational oblateness from visual measurements of the geometric oblateness, and more generally a dynamical flattening. Results are given for different observed rotational laws. It is shown that the surface oblateness is surely upper bounded by 11 milliarcsecond. As a consequence of the observed surface and sub-surface differential rotation laws, we deduce a measure of the two first gravitational harmonics, the quadrupole and the octopole moment of the Sun: J ₂=−(6.13±2.52)×10⁻⁷ if all observed data are taken into account, and respectively, J ₂=−(6.84±3.75)×10⁻⁷ if only sunspot data are considered, and J ₂=−(3.49±1.86)×10⁻⁷ in the case of helioseismic data alone. The value deduced from all available data for the octopole is: J ₄=(2.8±2.1)×10⁻¹². These values are compared to some others found in the literature. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005238718479     

Accounting for the viscosity of the fluid core in the problem of the physical libration of the moon

A two-component theoretical model of the physical libration of the Moon in longitude is constructed with account taken of the viscosity of the core. In the new version, a hydrodynamic problem of motion of a fluid filling a solid rotating shell is solved. It is found that surfaces of equal angular velocity are spherical, and a velocity field of the fluid core of the Moon is described by elementary functions. A distribution of the internal pressure in the core is found. An angular momentum exchange between the fluid core and solid mantle is described by a third-order differential equation with a right-hand side. The roots of a characteristic equation are studied and the stability of rotation is proved. A libration angle as a function of time is found using the derived solution of the differential equation. Limiting cases of infinitely large and infinitely small viscosity are considered and an effect of lag of a libration phase from a phase of action of an external moment of forces is ascertained. This makes it possible to estimate the viscosity and sizes of the lunar fluid core from data of observations.     

On some problems concerning the calculation of the form of the magnetopause and the electric field on the magnetopause in the framework of the continuum medium model

In order to understand the reason of the existence of the electric field in the magnetosphere, and for the theoretical evaluation of its value, it is necessary to find the solution of the problem of determination of the magnetosphere boundary form in the frameworks of the continuum medium model which takes into account part of the magnetospheric plasma movement in supporting the magnetospheric boundary equilibrium. A number of problems for finding the distribution of the pressure, the density, the magnetic field and the electric field on the particular tangential discontinuity is considered in the case when the form of discontinuity is set (the direct problem) and a number of problems for finding the form of the discontinuity and the distribution of the above-mentioned physical quantities on the discontinuity is considered when the law of the change of the external pressure along the boundary is set (for example, with the help of the approximate Newton equation). The problem which is considered here, which deals with the calculation of the boundary form and with the calculation of the distribution of the corresponding physical quantities on the discontinuity of the 1st kind for the compressible fluid with the magnetic field with field lines which are perpendicular to the plane of the flow in question, concerns the last sort of problems. The comparison of the results of the calculation with the data in the equatorial cross-section of the magnetosphere demonstrates that the calculated form of the boundary, the value of the velocity of the return flow and the value of the electric field on the magnetopause, agree satisfactorily with the observational data.