天球参考系实现中的问题评述

本文评述了在建立历表参考架和恒星参考架过程中所面临的问题和困难，回顾了建立河外射电天球参考架的发展历史，并介绍了其目前状况，讨论了河外射电天球参考架在与其他天球参考架连接过程中所遇到的问题及其可能的解决途径。     

关于天球参考报

章动序列计算和地球定向参数测定需要一个中间的天球参考极作参照，1984年，采用IAU1980章动理论，选取天球历书极作为参考极，利用改善岁差章动模型和由天文测地新技术确定地球定向参数实现的天球历书极，其精度可达0．1mas，随着理论和观测精度的提高，在微角秒量级下，章动和极移模型中周日和半周日成分分应被考虑，地球定向参数的高频成分已被测定，因此天球历书极的原先定义不再适用，需要更改，叙述了不同天球参考极的概念，天球历书极的定义，评述了天球历书极目前实现及其缺陷，介绍了新的天球参考极－天球中间极的定义及其实现。     

空间时代地面光学天体测量的意义

从基本天体测量的主要任务出发，介绍了绝对测定和相对测量之间的区别和不同用途，并针对河外射电源参考架和依巴谷参考架的高精度的不足之处，说明了地面光学天体测量的长期性和灵活性等优势正是克服这些不足之处所必须的，但这不应是传统的已有精度下的地面光学天体测量，而应是与空间测量精度可比的要求下的地面测量，两者配合起来，将能促进本学科和相关学科的发展。     

基于SLR精密轨道的天文定位精度分析

利用全球卫星激光测距服务系统(ILRS,International Laser Ranging Service)标准点资料对Ajisai卫星进行精密定轨,残差均方根(RMS)优于3 cm,得到该星的精密轨道.进而对长春站40 cm空间碎片光电望远镜获得的Ajisai卫星的天文定位资料进行精度分析,外符合精度约3″左右.单独利用天文定位数据进行轨道改进,内符合精度优于3″.改进轨道的x、y、z坐标3分量在观测数据覆盖范围内的精度在100 m之内.同样地对Jason-1卫星作数据分析,结果和Ajisai卫星精度相当.分析各个弧段的精度变化,发现定标星个数减少,会导致天文定位精度下降.据此提出可以把最少定标星比例作为评定数据质量的参考指标之一.     

最新规范的参考系及有关问题

在简要阐明参考系、参考架及其历史重大进程的基础上,对几种重要的、最新规范的参考系/参考架(质心天球参考系和地心天球参考系、国际天球参考系、国际地球参考系、太阳系动力学参考系等)的定义、实现和特点作了评述和分析,并对最新规范中与参考系、参考架有关的某些新概念的定义和新模式的应用(自2003年开始贯彻),如:天球中介极(CIP)、天球历书原点(CEO)、地球历书原点(TEO)、地球自转角的新定义、岁差-章动新模式的应用,作了阐述和讨论。     

天球和地球历书原点

国际天球参考系的使用、观测精度的提高和方法的改善要求采用与地球轨道运动无关的运动赤道上的起算点，Guinot提出的非旋转原点可作为这样一种选择。非旋转原点依赖于天球参考极。IAU决定从2003年起采用天球中间极作为天球参考极。非旋转原点在天球参考系的使用，可给出在天球中间极赤道上的天球历书原点，非旋转原点在地球参考系的使用，可给出在天球中间极赤道上的地球历书原点。回顾了非旋转原点的概念、以历书原点为参考的天球参考系和地球参考系的坐标变换，经出了在微角秒精度下天球参考极的坐标和历书原点的位置，讨论了采用历书原点对测定UT1的影响，指出当岁差章动模型、天极补偿、分点改正得到改善时，基于历书原点的UT1定义不需要更改，从而保证了UT1的连续。     

Techniques for positional measurements of telescopic meteor TV images

We present the results of our positional reduction of the observational material obtained using a meteor patrol based on a Schmidt telescope and a TV CCD detector. More that 1000 telescopic meteors were recorded in three years of meteor patrolling. Techniques for the cataloging and positional reduction of 3050 TV images with meteor trails are described. We have developed a technique for measuring the images of reference stars to determine the rectangular coordinates in the image frame. We discuss the achieved accuracy of determining the equatorial coordinates of reference and check stars by Turner’s method (of the order of a few arcseconds). We have developed software that allows the rectangular coordinates of meteor trajectory points to be determined after the meteor image reduction. These coordinates are used to determine the equatorial coordinates of the poles of the great circles of meteor trajectories (the angular length is not less than 15′ with an accuracy of at least 4′. We consider the possibility of using Stanyukovich’s method to determine the equatorial coordinates of radiants for non-basis meteor observations. The accuracy of determining the radiant coordinates has been estimated to be 4′–5′. Prospects for obtaining the kinematic characteristics of meteor particles are discussed.     

Distortion of the stellar velocity field parameters due to systematic variations of parallaxes over the celestial sphere

We study the effect of systematic variations in stellar parallaxes over the celestial sphere on the results of a kinematic analysis of stellar proper motions. Our approach is based on the representation of stellar parallaxes by scalar spherical harmonics and on the decomposition of stellar proper motions into a system of vector spherical harmonics. We derive theoretical relations that relate the coefficients of the decomposition of stellar proper motions into toroidal and spheroidal harmonics to the coefficients of the decomposition of stellar parallaxes into scalar spherical harmonics. We have established that the systematic variations of parallaxes over the celestial sphere distort all parameters of the linear Ogorodnikov-Milne model and can be responsible for the appearance of beyond-the-model harmonics. We have performed a kinematic analysis of the proper motions of blue-white and red giants based on Hipparcos data. The parallaxes of blue-white giants show a strong dependence on Galactic latitude (with predominant contraction along the Galactic equator). In contrast, the deviations of the parallaxes from the mean for red giants are localized only in two regions of the celestial sphere. For these samples, the effect of parallax variations over the celestial sphere on kinematic parameters has turned out to be comparable to their rms errors. The global solutions performed using both samples have revealed strong beyond-the-model kinematic effects described by second-order toroidal harmonics and third-order spheroidal harmonics. Using the solutions performed separately in the northern and southern Galactic hemispheres, we have established that not the systematic variations of parallaxes over the celestial sphere but the retardation of Galactic rotation with increasing distance of stars from the principal Galactic plane is mainly responsible for the appearance of these harmonics. Based on these samples of stars, we have estimated the magnitude of the vertical Galactic rotation velocity gradient to be 18.0±2.9 and 22.7±2.2 km s^?1 kpc^?1, respectively.     

自行与银河系研究的前沿

简述了精确测定相对自行的方法,特别介绍了在用2～3个历元的底片和CCD观测结果推导恒星自行的过程中如何消除光学视场畸变、星等差和色差的具体办法;并介绍了用星系把相对自行推算绝对自行的方法。还介绍了用自行资料研究银河系结构和演化的一些前沿课题,其中包括星团研究、与银河系兼并的矮星系的发现、暗物质的检测、外星行星的探测和银河系中心黑洞的质量估算等。最后评价了自行在研究银河系中的重要性,论述了我国研制4m光学/近红外望远镜的重要意义。     

近10年我国天体测量的发展

简述天体测量学研究的内各以及与各相关学科之间的关系；描述近10年来国际天体测量研究的进展和前沿课题；叙述我国天体测量研究的历史背景和研究基础，以及近10年来在国家自然科学基金委员会和其他科学组织支持下取得的成果，并对今后10～20年我国天体测量的发展提出初步看法。     

The Earth's rotation: Definition of the pole and of the angle of sidereal rotation

The use of new techniques for measuring the Earth's orientation in space and the intrinsic qualities of their attached terrestrial and celestial reference frames have now raised the accuracy of the computed polar coordinates and the angle of sidereal rotation to a level usually better than 0.001. The conceptual and conventional definitions of the Earth's pole of rotation and of the Universal Time UT1 must accordingly be given with the same order of precision. This paper gives a review of the past and present definitions of the celestial pole and UT1 as well as an evaluation of their deficiencies. Some necessary improvements in these definitions are proposed.     

On the variation of specific angular momentum among Main Sequence stars

The specific angular momentum is found to vary with mass for earlier and later-type Main Sequence stars. Of various plausible causes, the difference in the interior density distribution of earlier and later-type stars is not sufficient enough to explain the difference either in angular momentum or in its gradient between earlier and later-type stars. The non-rigid rotation, however, may account for this difference in specific angular momentum as well as its gradient, if faster angular velocity in the interior for later-type and/or slower angular velocity for earlier-type stars than the surface value is allowed. A few other possibilities have also been briefly considered to understand this difference.     

Pulsating sdB Stars: A New Approach to Probing their Interiors

Horizontal branch stars should show significant differential rotation with depth. Models that assume systematic angular momentum exchange in the convective envelope and local conservation of angular momentum in the core produce HB models that preserve a rapidly rotating core. A direct probe of core rotation is available. The nonradial pulsations of the EC14026 stars frequently show rich pulsation spectra. Thus their pulsations probe the internal rotation of these stars, and should show the effects of rapid rotation in their cores. Using models of sdB stars that include angular momentum evolution, we explore this possibility and show that some of the sdB pulsators may indeed have rapidly rotating cores.     

On the accuracy of approximation of motion of a small celestial body by intermediate perturbed orbits calculated on the basis of three position vectors and three observations

Intermediate perturbed orbits, which were proposed earlier by the first author and are calculated based on three position vectors and three measurements of angular coordinates of a small celestial body, are examined. Provided that the reference time interval encompassing the measurements is short, these orbits are close in the accuracy of approximation of actual motion to an orbit with fourth-order tangency. The shorter the reference time interval is, the better is the approximation. The laws of variation of the errors of methods for constructing such intermediate orbits with the length of the reference time interval are formulated. According to these laws, the rate of convergence of the methods to an exact solution in the process of shortening of the reference time interval is, in general, three orders of magnitude higher than that of conventional methods relying on an unperturbed Keplerian orbit. The considered orbits are among the most accurate of their class that is defined by the order of tangency. The obtained theoretical results are verified by numerical experiments on determining the orbit of 99942 Apophis.     

未来的国际天球参考架

本文简述了国际天球参考架的发展历史和现在射电参考架的现状—基准源选择的标准和参考架的稳定性。描述了地面上光学观测在依巴谷参考架的维持和加密的一系列工作。介绍由天体测量卫星GAIA和SIM给出的天球参考架可能逵到的精度。详述了在今后十年中地面天体测量的作用以及正在开展有关天球参考架的研究课题 ,同时也列出了我国正在和即将开展天体测量的几个研究课题     

Tidal Angular Momentum in Close Binary Systems in presence of Wind Driven Non-conservative Mass Transfer with Uniform Mass Accretion Rate

A very well-known property of close binary stars is that they usually rotate slowly than a similar type single star. Massive stars in close binary systems are supposed to experience an exchange of mass and angular momentum via mass transfer and tidal interaction, and thus the evolution of binary stars becomes more complex than that of individual stars. In recent times, it has become clear that a large number of massive stars interact with binary companions before they die. The observation also reveals that in close pairs the rotation tends to be synchronized with the orbital motion and the companions are naturally tempted to invoke tidal friction. We here introduce the effect of tidal angular momentum in the model of wind driven non-conservative mass transfer taking mass accretion rate as uniform with respect to time. To model the angular momentum evolution of a low mass main sequence companion star can be a challenging task. So, to make the present study more interesting, we have considered initial masses of the donor and gainer stars at the proximity of bottom-line main sequence stars and they are taken with lower angular momentum. We have produced a graphical profile of the rate of change of tidal angular momentum and the variation of tidal angular momentum with respect to time under the present consideration.     

Some Aspects of Relativistic Astrometry from Within the Solar System

In this article we outline the structure of a general relativistic astrometric model which has been developed to deduce the position and proper motion of stars from 1 µarcsecond optical observations made by an astrometric satellite orbiting around the Sun. The basic assumption of our model is that the Solar System is the only source of gravity, hence we show how we modeled the satellite observations in a many-body perturbative approach limiting ourselves to the order of accuracy of (v/c)². The microarcsecond observing scenario outlined is that for the GAIA astrometric mission.     

Equations of radiation gas dynamics in tetrad form for astrophysical applications

This paper deals with the representation of relativistic equations of gas dynamics with due regard to the general relativity theory effects in the form accepted and widely applied in the special relativity theory. With this purpose, a strict formal definition of a non-inertial co-moving reference frame without rotation is carried out on the basis of a tetrad formalism by use of the Fermi—Walker rules of transport of 4-frame. The equations of physical kinetics, relativistic collapse, Einstein's equations, equations of relatiivistic radiation gas dynamics for ideal and dissipative gases, Taub's equations for a shock wave, which allow for radiation and electron-positron pairs, are obtained in this reference frame. On the basis of the local Lorentz transformation and the Ricci rotation coefficients, these equations are written in the laboratory reference frame, in order to illustrate the fact that the general relativity effects can be simply taken into account in the equations having a form accepted in the special relativity theory.     

HIPPARCOS and the dynamics of the solar system

The HIPPARCOS program may contribute to dynamical astronomy in two different ways: by determining the positions of some bodies of the solar system or by improving the positions of the reference stars with respect to which observations of members of the solar system are made.It is shown that only minor planets may be observed validly by HIPPARCOS but these observations alone cannot contribute significantly to the determination of a reference frame. However, they can be useful for the improvement of orbits and as a complement to a major observational effort in preparation of a new determination of dynamical system of reference.HIPPARCOS will provide a new global reference frame and improved proper motions of stars. This may be used to rediscuss earlier observations and provide corrections to the theory of motion of the Moon and planets. Such corrections may be rather large and their possible effect is indicated for several cases. Furthermore, the celestial reference system of HIPPARCOS will allow to avoid, in future observations, many of the presently existing biases.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.     

Rotation Profiles of Solar-like Stars with Magnetic Fields

We investigate the rotation profile of solar-like stars with magnetic fields. A diffu-sion coefficient of magnetic angular momentum transport is deduced. Rotating stellar models with different mass incorporating the coefficient are computed to give the rotation profiles. The total angular momentum of a solar model with only hydrodynamic instabilities is about 13 times larger than that of the Sun at the age of the Sun, and this model can not reproduce quasi-solid rotation in the radiative region. However, the solar model with magnetic fields not only can reproduce an almost uniform rotation in the radiative region, but also a total angular momentum that is consistent with the helioseismic result at the 3 σ level at the age of the Sun. The rotation of solar-like stars with magnetic fields is almost uniform in the radiative region, but for models of 1.2-1.5 M⊙, there is an obvious transition region between the convective core and the radiative region, where angular velocity has a sharp radial gradient, which is different from the rotation profile of the Sun and of massive stars with magnetic fields. The change of angular velocity in the transition region increases with increasing age and mass.