FK5星表系统差讨论

比较了Ｊ２０００．９年的ＦＫ５和依巴谷结果的位置和自行,表明了ＦＫ５星表有较大的系统差。另外,我们亦将在ＦＫ５系统中的运动中和上海天文光电等高星表和依巴谷测作了比较,同样反出类似的ＦＴ５星表系统差。     

利用地球定向参数确定依巴谷输入星表与射电天球参考架之间的旋转

通过比较地球定向参数（ＥＯＰ）序列和对应的地固参考架，本文得到了依巴谷输入星表（ＨＩＣ）和国际地球自转服务（ＩＥＲＳ）基于甚长基线干涉测量（ＶＬＢＩ）建立的河外天球参考架（ＩＣＲＦ）之间的旋转参数，在Ｊ２０００．０历元，前者至后者的旋转参数为［８．４±１．１ｍａｓ，４６．７±１．１ｍａｓ，４５．５±１．５ｍａｓ］，其时间变率为［－０．１４±０．０５ｍａｓ／ａ，３．２２±０．０５ｍａｓ／ａ，５．７０±０．０７ｍａｓ／ａ］。依巴谷输入星表是完全基于ＦＫ５系统的，本文得到的旋转参数与ＩＣＲＦ和ＦＫ５之间的系统差异情况相符     

FK5相对于依巴谷星表的系统差及其对EOP的影响

依巴谷星表在建立时已做到与以河外射电源定义的国际天球参考系（ICRS）相符合,而ICRS系统与由FK5星表实现的由J2000.0平赤道和平春分点定义的赤道坐标系统相一致。估计依巴谷星表的系统误差小于0.1mas,因此,依巴谷星表成为描述光学观测确定的地球定向参数（EOP）的一个更为均匀的参考系。本文主要讨论了FK5和依巴谷星表之间的星表系统差（FK5－Hip）,并用中国光电等高星表来检验（FK5－Hip）星表系统差的结果,并估算了星表系统差（FK5－Hip）对EOP的影响。     

观测射电星联系依巴谷星表和地面光学星表自行的精度估计

用蒙特卡罗方法对佘山40厘米望远镜射电星的观测模拟，由照相测定的自行来估计依巴谷星表和光学星表自行间联系的精度。结果表明由90颗星估计的联系精度为0″.16／百年。     

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。     

测定天文大气折射和建立电磁波折射延迟实测模型(Ⅱ)-采用依巴谷星表作为工作星表

叙述了测定大气折射对工作星表的要求和星表系统误差的影响,并通过FK5星表相对于依巴谷星表的系统误差,来说明以往的各种基本星表都不适用的原因;文章说明了依巴谷星表所列星位置不含随天区而异的系统误差的特性,分析了该星表问世时的精度和十多年后的今天仍能达到的精度,说明它可以作为这种测定的工作星表,从而为直接测定天文大气折射值和折射率差提供了一个重要的条件;文章还介绍了依巴谷星表的星等分布,认为只需选用亮于6mag的依巴谷星,这一星等范围,为制定专用测量仪器终端的设计方案提供了依据。     

依巴谷天文卫星及其输入星表数据库

本文简要介绍了欧洲空间局通过阿利亚那火箭发射的依巴谷天文卫星,也概述了为依巴谷卫星探测计划服务,并积累和编辑其观测资料的输入星表数据库。     

国际天球参考系

阐述了１９９８年１月４日起ＩＡＵ采用的天球参考系的定义,以及它与以往采用的光学天球参考架ＦＫ５的关系。介绍了国际天球参考系在射电波段的实现过程,其稳定性的维持方法和它与依巴谷星表之间的关系。重点描述了影响国际天球参考架稳定性的物理因素－河外射电源的结构及其变化,射电源喷流的视超光速现象和由银河系盘星和大质量致密晕的引力透镜效应引起的视自行等。     

依巴谷参考架惯性特征

通过分析和比较依巴谷自行系统与FK2．0自行系统之间的关系，研究了依巴谷系统的惯性问题，指出该系统可能然存在较大的非惯性剩余旋转。     

用依巴谷星表归算光电等高仪I型在伊尔库茨克的观测

陕西天台（ＣＳＡＯ）和俄罗斯东西伯利亚物理技术和无线电工程测量研究所（ＶＳＮＩＦＴＲＩ）之间进行的高等仪合作观测研究已进行了三年多,到１９９９年上半年完成了两部纳要的观测,获得了两部无赤续盲区的等高仪星表,主要介绍两部纲要的观测精度（相对依巴谷星表系统）,星入正精度和某些系统误差的分析。从各个方面来看,都达到了预期的合作目标。     

空间参考系自行系统与地面自行系统

针对地面FK5和空间依巴谷自行系统 ,采用银河系运动学分析方法发现 ,即使考虑了岁差改正的影响 ,两种自行系统之间仍存在很大差异。用建立在FK5系统上的PPM和ACRS自行与依巴谷自行比较 ,发现FK5自行系统内部存在非刚性运动 ;同时无法用VLBI及LLR所测定的岁差改正值来解释FK5与依巴谷自行系统的关系。     

岁差常数改正及 FK5和Hipparcos自行系统

许多研究结果表明,FK5和Hipparcos自行系统的关系,与VLBI和LLR所测定的岁差常数改正值不相符合．利用建立在FK5系统上的PPM和ACRS自行数据的分析,通过多个子样本的考察,发现不论由PPM或ACRS自行资料,都无法给出一致的岁差改正值和分点运动改正值．从而表明,FK5自行内部的系统差是产生这种问题的主要因素．     

Error analysis of proper motions in decination obtained for 807 Hipparcos stars from PZT observations over many decades

After publication of the Hipparcos catalogue (in 1997), a few new astrometric catalogues have appeared (TYCHO‐2, ARIHIP, etc.), as a good combination of the Hipparcos satellite and ground‐based data, to get more accurate coordinates and proper motions of stars than the Hipparcos catalogue ones. There are also investigations on improving the Hipparcos coordinates and proper motions by using the astrometric observations of latitude and universal time variations (via observed stars referred to Hipparcos catalogue), together with Hipparcos data, carried out during the last few years. These kind of ground‐based data were collected at the end of the last century by J. Vondrák. There are about 4.4 million optical observations made worldwide at 33 observatories and with 47 instruments during 1899.7–1992.0; our Belgrade visual zenith telescope data (for the period 1949.0‐1986.0) were included. First of all, these data were used to determine the Earth Orientation Parameters – EOP, but they are also useful for the opposite task – to check the accuracy of coordinates and proper motions of Hipparcos stars which were observed from the ground over many decades. Here, we use the latitude part of ten Photographic Zenith Tubes – PZT data (more than 0.9 million observations made at 6 observatories during the time interval 1915.8–1992.0), and combine them with the Hipparcos catalogue ones, with suitable weights, in order to check the proper motions in declination for 807 common PZT/Hipparcos stars (and to construct the PZT catalogue of μ_δ for 807 stars). Our standard errors in proper motions in declination of these stars are less than or equal to the Hipparcos ones for 423 stars. The mean value of standard errors of 313 stars observed over more than 20 years by PZT is 0.40 mas/yr. This is 53% of 0.75 mas/yr (the suitable value from the Hipparcos catalogue). We used the Least Squares Method – LSM with the linear model. Our results are in good agreement with the Earth Orientation Catalogue – EOC‐2 and the new Hipparcos ones. The main steps of the method and the investigations of systematic errors in determined proper motions (the proper motion differences with respect to the Hipparcos values, the EOC‐2 ones and the new Hipparcos ones, as a function of α, δ, and magnitude) are presented here. A comparison of the four catalogues by pairs shows that there is no significant relationship between the differences of their μ_δ values and magnitudes and color indices of the common 807 stars. All catalogues have relatively small random and systematic errors which are close to each other. However, the comparison shows that our formal errors are too small. They are underestimated by a factor of nearly 1.7 (for EOC‐2, it is 2.0) if we take the new Hipparcos (or Hipparcos) data as reference (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

星表系统差及其计算方法

本文对星表系统差的性质进行了讨论，并分析和评估了目前常用的星表系统差计算方法的优、缺点，从而提出了一个新的星表系统差计算方法．同时也提出了星表系统差计算精度的检验标准．最后对用不同方法计算的系统差进行了分析比较．结果表明，新方法的系统差计算精度好于目前常用的解析方法．     

Comparison of the four catalogues by pairs,the Hipparcos,new Hipparcos,EOC‐2 and IL,by using μδ for the common 1120 stars

We present comparison results of our Independent Latitude (IL) catalogue of μ_δ determinations for 1120 bright stars with the Hipparcos, new Hipparcos and Earth Orientation Catalogue (EOC‐2) values. Also, we took into consideration the EOC3 and EOC4 (recent versions of EOC catalogues). Our μ_δ values are based on zenith telescope observations from seven Independent Latitude (IL) observatories. The IL measures are spanning a time baseline of up to 90 years which is the key advantage to the accurate determination of μ_δ. The short interval of the Hipparcos satellite observations is a disadvantage for a good accuracy of stellar proper motion, especially in the case of double and multiple stars. For this reason many astrometric catalogues have appeared after the publication of the Hipparcos including our IL catalogue. These catalogues are an appropriate combination of the Hipparcos satellite and ground‐based data which yields more accurate stellar coordinates and/or their proper motions. Among various types of ground‐based observations the latitude and universal time variations obtained from several million observations of stars reduced to the Hipparcos reference system were used for this purpose. These observations were obtained during almost the entire last century and were originally used to determine the Earth Orientation Parameters. It is also possible to use these data in the inverse task of checking the accuracy of stellar coordinates and/or their proper motions listed in the Hipparcos Catalogue. Such latitude and universal time variations data are the basis of the EOC and IL catalogues. In this paper, we computed the differences in μ_δ values between pairs of catalogues and analyzed the results to characterize the μ_δ errors for the four catalogues with a special focus on our IL catalogue. The standard errors of μ_δ for IL stars observed over more than 20 years are mostly smaller than or equal to the Hipparcos errors, and close to the accuracy level of the EOC‐2 (EOC‐3, EOC‐4) and the new Hipparcos. The resulting investigations of errors of differences of μ_δ, show that all four catalogues have relatively small random and systematic errors which are close to each other meaning that the corresponding μ_δ values have a high accuracy. Our sample also contains detected double and multiple stars for which the effects of the orbital and proper motions are difficult to separate. The differences of μ_δ values for these stars generally exceed those obtained for single stars. Also, these discrepancies could be attributed to effect of possible, still unrecognized, astrometric binaries. These investigations about the proper motions and double stars are in line with the activity of the IAU Working Group on Astrometry by Small Ground‐Based Telescopes. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Duplicity amongst HIPPARCOS stars

Stars observed by the astrometry satellite Hipparcos may be unknown double stars. A subsample of those are dangerous for the extragalactic link of Hipparcos proper motions by long-term photographic proper motions, if the time base of Hipparcos is too short to detect the orbital motion. The probability of these cases and the typical size of the photocentric orbital motion are estimated by Monte Carlo simulations for the sample of 33 stars used in the Bonn extragalactic link. Both are found to be considerable: about 16% and 9 mas/yr respectively.     

Binary statistics from Hipparcos data – a progress report

The Hipparcos data are an important source for constraining the statistical distribution functions for the binaries in the general field. The present study uses the resolved binaries (separation 0.1‐10 arcsec, magnitude‐differences below 4 mag) to check directly the frequency of main‐sequence binaries with (linear) separations 30‐500 a.u. and mass‐ratios 0.6‐1.0. Complete Hipparcos samples have limiting apparent magnitudes brighter than mag 8, and contain therefore rather few stars. By modelling the completeness using the Tycho observations (complete to mag 10), we may increase substantially the number of useable Hipparcos stars while keeping a tolerable level of systematic uncertainty. The results, for stellar masses not much above solar, show binary frequencies typically a factor two above those usually assumed. Also, although the mass‐ratio distribution function generally decreases towards larger q, there is a definite narrow peak at q = 1. In order to use the Hipparcos data to full advantage, a more indirect approach is necessary. By modelling both the local Galaxy and the Hipparcos observations, one may put constraints also on the number of closer binaries which show up in the Hipparcos Catalog as non‐linear proper motions.     

Proper motions in the field of the globular cluster NGC 6934

We measured relative proper motions with a typical accuracy of 1.0 milliarcsec/year (mas/a) for 2000 stars in a 1°4 × 1°4 field around the low-latitude globular cluster NGC 6934. Four plates taken with the Bonn double refractor, spanning an epoch difference of 62 years, were digitized completely. Within the tidal radius of the cluster, we find 106 stars with proper motion errors less than 5 mas/a. Membership probalilities are computed taking into account the individual proper motion errors and the radial distances to the cluster centre. We derive the mean relative proper motion of NGC 6934 using stars with high membership probabilities from radial velocities (Smith and Bell 1986) or from their location in the colour-magnitude diagram (Harris and Racine 1973). The relative proper motions of four Hipparcos stars in the field will be used to obtain the absolute proper motion of NGC 6934 once the extragalactically calibrated Hipparcos Output Catalogue is available.     

The proper-motion signal of unresolved binaries in the Hipparcos catalogue

We present an investigation of the differences between quasi-instantaneous stellar proper motions from the Hipparcos catalogue and long-term proper motions determined by combining Hipparcos and the Astrographic Catalogue. Our study is based on a sample of about 12000 stars of visual magnitude from 7 to 10 in two declination zones on the northern and equatorial sky. The distribution of the proper-motion differences shows an excess of large deviations. This is caused by the influence of orbital motion of unresolved binary systems. The proper-motion deviations provide statistical evidence for 360 astrometric binaries in the investigated zones, corresponding to about 2400 such binaries in the entire Hipparcos catalogue, in addition to those already known. In order to check whether the observed deviations are compatible with standard assumptions on the basic parameters of binary stars, we model the impact of orbital motion on the observed proper motions in a Monte Carlo simulation. We show that the simulation yields an acceptable approximation of the observations, if a binary frequency between 70% and 100% is assumed, i.e.if most of the stars in the sample are assumed to have a companion. Thus Hipparcos astrometric binaries confirm that the frequency of non-single stars among field stars is very high. We also investigate the influence of the mass function for the secondary component on the result of the simulation. A constant mass function and mass functions with moderate increase towards low masses lead to results, which are compatible with the observed proper-motion effects. A high preponderance of very-low-mass or substellar companions as produced, for example, by a M^—1 power law is not in agreement with the frequency of proper-motion deviations in our sample of stars.