发生在1～2GHz的Ⅲ型爆发

对北京天文台动态频谱仪1996～1999年观测到的68群Ⅲ型爆发作了统计分析,并对这些事件的频率漂移、持续时间、偏振和带宽的基本特性作了定性分析.     

Projection Effects on Physical Parameters Obtained from Solar Vector Magnetograms

1 INTRODUCTION Magnetic field plays an important role in solar activity. The stressing and subsequent partialrelaxation of magnetic fields in the active regions are generally accepted to be the energy sourceof solar flares. To quantitatively study the extent of stressed magnetic field as distinct from itspotential field, Hagyard et al. (1984) defined a magnetic shear angle膖he azimuth differencebetween the observed transverse magnetic field vector and the computed potential field vectorth…     

中性大气折射映射函数和大气折射母函数方法

回顾了作为实用天文学和大地测量学中基本研究课题之一的大气折射函数研究的最新进展;介绍了近几年发展的大气折射母函数方法。对如今广泛地应用在空间测量技术中的几种映射函数,如ＣｆＡ２．２、ＭＴＴ等模型作出评述;特别分析了ＮＭＦ模型的优点和不足之处。还介绍了由大气折射母函数方法引出的大气延迟新连分式映射函数和天文大气折射的映射函数方法,利用ＶＬＢＩ实验中高度截止角与基线长变化的关系和探空气球（ｒａｄｉｏｓ     

A Possible Means of Improving the Accuracy of Refraction Delay Correction of Neutral Atmosphere

The space geodetic technology requires an accurate model of correction of refraction delay by the neutral atmosphere that varies from one observing station to another, and from one azimuth to the next. It is pointed out that under the present condition the astronomical refraction can not yet be directly determined, any correction model because of its high dependence on the assumed atmospheric distribution, is incapable of achieving the required accuracy or of improving the cut-off altitude. In this paper, based on the special properties of the lower latitude meridian circle at Yunnan Observatory and our experience of determining atmospheric refraction therewith, a new method is proposed for improving the accuracy of refraction delay correction. Namely, the measured data of astronomical refraction of an observing station from near zenith to low altitudes in different azimuths are used to evaluate the refractivities and the parameters of the mapping functions, thereby establishing a model of atmospheric refraction delay correction that varies with the observing station and the azimuth. Since it is unnecessary for the new method to adopt any atmospheric distribution model, application of this new method will improve correction accuracy of refraction delay to better than 1mm at zenith and to centimeters at low altitudes, and improve the cut-off altitude to below 5 degrees.     

大气折射母函数方法、大气折射解析解和映射函数

回顾了作为实用天文学和大地测量学中基本研究课题之一的大气折射映射函数研究的进展。介绍了近几年上海天文台发展的大气折射母函数方法 ,以及由此导出的大气折射解析解。对如今广泛地应用在空间测量技术中的几种映射函数做出评述 ;分析了NMF模型的优点和不足之处。介绍了由大气折射母函数方法引出的大气延迟新连分式映射函数和天文大气折射的映射函数方法。利用VLBI实验中高度截止角与基线长度重复率的关系、探空气球 (radiosonde)观测资料、PRARE资料比较了各种映射函数的结果。特别指出了映射函数方法对天文大气折射和光学波段测距精度的改进。讨论了大气折射计算中的主要误差源。     

提高中性大气折射延迟改正精度的可能途径

针对空间大地测量技术对中性大气折射延迟改正精度的要求,阐述了折射延迟改正值应随测站和随方位而异的必要性．指出,在尚不能直接测定天文大气折射值的情况下,现有的各种改正模型对大气分布模型的依赖性,不能达到预期的精度和降低观测的截止角．根据云南天文台低纬子午环的特殊结构,和测定大气折射的实践,提出了提高折射延迟改正精度的新方法,即：利用各观测站不同方位从天顶附近直到低地平高度角的天文大气折射实测数据,求解得到折射率差和映射函数的参数,从而建立随测站和随方位而异的大气折射延迟改正模型．这一新方法的实施,将能在不需采用大气分布模型的情况下,把天顶延迟的改正精度提高到1 mm以内,低地平高度角的折射延迟改正精度提高到厘米级,并且把截止高度角压缩到5°以内．     

Signal loss due to imperfect fringe rotation in VLBI correlators revisited

This not new problem is analysed in view of discrepancies met in the literature. Practical formulae for calculation of the signal-to-noise ratio losses caused by quantization of the lobe rotation function in digital VLBI correlators are derived. Examples are given for a few simpler rotation schemes.     

Improvement on Atmospheric Hydrostatic Delay Correction at Low Elevation Angles

Observation made at low evelation angles is the trend of development of GPS (Global Positioning System) meteorology, wherein the development of highly accurate atmospheric hydrostatic delay corrections at low elevating angles is the main key technique. The comparison among three methods for calculating the atmospheric hydrostatic delay correction of the radio waves from space to the ground-based receiver is made: (1) the atmospheric hydrostatic delay obtained from the path integration of the sounding balloon data under the assumption of atmospheric spherical symmetry, (2) the atmospheric hydrostatic delay acquired from the reanalyzed data of the NCEP (National Centers for Environmental Prediction) under the assumption of atmospheric spherical symmetry and (3) the atmospheric hydrostatic delay got from Niell's atmospheric hydrostatic mapping function. The results of the comparison of them with the atmospheric hydrostatic mapping function obtained from the calculation carried out by taking advantage of the data acquired at 89 sounding balloon stations in China in 2001 show that the accuracy of the method of the path integration of the reanalyzed data of NCEP at low elevating angles (bellow 5°) is about 5 times better than that of the Niell mapping function model.     

On Astronomical Atmospheric Refraction

Through a comparison between the series expression and mapping function expression of the astronomical refraction, we believe that, as far as a specific atmospheric refraction model is concerned, the computational accuracy is not lower in the former than in the latter, and that the convergence is poorer in the theoretically derived series expression, because of the different approximations made. From an analysis of the method of generating function of the atmospheric refraction mapping function it is considered that this kind of method can not embody the characteristics of geophysics and atmospheric physics. It is pointed out from the comparison that the atmospheric refraction model which is constructed by adopting the specific atmospheric distribution of a certain place does not apply to all other places and cannot be used to evaluate the other atmospheric refraction models. For improving the correction accuracy the key lies in the adoption of an effective method by which the instantaneous refraction values at different positions are directly determined to construct a local, position-dependent model of atmospheric refraction observation.     

Path Bending Correction for Refraction Delay of Electromagnetic Waves

Focusing on lowering the cut-off elevation in the neutral atmosphere refraction delay correction and on raising the accuracy of the correction, we derive the formulae for calculating the correction for the bending of the light path caused by atmospheric refraction. This is the sort of correction that is given after the principal term in theoretical models of neutral atmospheric refraction delay correction, but is often neglected because it is a small quantity. However, in practice, for a not too low elevation like 15°, this term reaches 1 cm order of magnitude and can not be neglected. Li Yan-xing et al. specially gave a derivation of this correction and a computational method by successive approximation and some calculated values. Yan Hao-jian also proposed a formula of direct calculation but his calculated result was more than 3 times smaller than that of Li Yan-xing, which shows that further study of this correction is called for. Here we give a simple, convenient and reliable formula for calculating the correction.     

A new simple method for the analytical solution of Kepler's equation

A new simple method for the closed-form solution of nonlinear algebraic and transcendental equations through integral formulae is proposed. This method is applied to the solution of the famous Kepler equation in the two-body problem for elliptic orbits. The resulting formulae are quite elementary and, beyond their analytical interest, they can also provide quite accurate numerical results by using Gausstype quadrature rules.     

IERS1996规范中地球引力势模型和测量模型的改进

简要而系统地介绍ＩＥＲＳ１９９６规范采用的地球引力势模型和各种测量模型,着重叙述了其与ＩＥＲＳ１９９２标准相比所作的改进。规范用ＪＧＭ－３地球引力势模型取代ＧＥＭ－Ｔ３模型,在计算地球潮汐形变产生的附加势时展开到３阶,并考虑了地幔的滞弹效应。在测站位移的计算中,规范引入了３倍洛夫数,计及地幔的滞弹性,引入了计算冰后期回弹的ＩＣＥ－４Ｇ模型,列出了改正ＶＬＢＩ观测中天线形变改正的公式。关于地球自转和     

低纬子午环配备CCD的误差理论分析

本文对ＬＬＭＣ＋ＣＣＤ仪器系统的误差理论进行了综合性的探讨。文中所涉及的误差主要来自两方面：其一是来自仪器系统本身的误差，其二是来自仪器系统以外的误差。论文的第一章对ＣＣＤ器件的特性及其在天文学上的应用作了扼要介绍；第二章阐述了低纬子午环配备ＣＣＤ的观测方法，还简述了低纬子午环的结构及观测原理；第三章对十七种不同类型误差的测定或消除方法作了详尽的探讨和分析；第四章推导了星径曲率改正；第五章对小角度天体测量技术和大角度天体测量技术进行了评估。     

发射线星系[OⅡ]λ3727/Hα谱线流量比的研究

利用从斯隆数字巡天(Sloan Digital Sky Survey,简称SDSS)第4次释放的光谱数据中选取的10~5个发射线星系样本,研究了[O_Ⅱ]λ3727/Hα流量比与星系尘埃消光、气体电离态和金属丰度的关系.发现尘埃消光改正对[O_Ⅱ]λ3727/Hα谱线流量比影响显著,消光改正前、后的[O_Ⅱ]λ3727/Hα谱线流量比的中值分别为0.48和0.89;尘埃消光改正后,F([O_Ⅱ]λ3727)-F(Hα)的弥散显著减小.贫金属星系的[O_Ⅱ]λ3727/Hα谱线流量比随星系气体的电离度增高而减小,而富金属星系不存在这种关系.另外,[O_Ⅱ]λ3727/Hα流量比与星系金属丰度相关.当12+lg(O/H)8.5时,星系[O_Ⅱ]λ3727/Hα流量比随金属丰度增加而下降;12+lg(O/H)8.5的星系,谱线流量比与金属丰度正相关.最后,利用气体电离度参数和星系的金属丰度,给出了计算不同类型星系[O_Ⅱ]λ3727/Hα流量比的公式.LAMOST望远镜将观测到大量红移z0.4的星系光谱,利用该公式可以给出星系的[O_Ⅱ]λ3727/Hα流量比,从而可以利用[O_Ⅱ]λ3727谱线流量计算z0.4星系的恒星形成率.     

Satellite prediction formulae for Vinti's model

For Vinti's dynamical problem, there is proposed a new form of solution wherein all three coordinates are expressed in terms of one independent variable. The formulae for the three co-ordinates are clear generalizations of the corresponding formulae for the Kepler problem while the independent variable corresponds to the true anomaly. The solution is completed by the relation connecting the independent variable with time: the latter is a generalization of the well known Kepler time-angle relationship. From the form and method of solution the main qualitative features of the motion are readily derived.     

Modelling RR Lyrae pulsation: mission (im)possible?

In order to make an in-depth comparison between theory and observations, we analyse the light and velocity curves of various hydrodynamical models simulating RRab stars. The observations are represented by empirical formulae, derived in this and our earlier papers. It is shown that the overwhelming majority of the models tested do not follow the empirical relations regarding the shape of the light curves and the physical parameters. In almost all cases the luminosities predicted from the model light curves are significantly lower than the corresponding model values. The overall discrepancy of the models is an important indication of the limitation of the applicability of the present theoretical light and velocity curves in the determination of the physical parameters of these stars. In transforming the theoretical data to the observed light curves in V colour and in computing the observed radial velocities, it is shown that both bolometric correction and tracing the line-forming regions have considerable effects on the evaluation of the observed quantities. In an effort to resolve the discrepancy between theory and observations, it is suggested that a proper evaluation of the bolometric correction and radial velocity based on complete dynamical atmosphere models may be a useful step in this direction.     

折射延迟改正模型

在分析了一些主要的天顸延迟改正模型，并对几种连分式形式的映射函数模型作了归纳后，认为：前者只能都基于大气球对称分布模型，采用差不多相同的各向同性的改正模型，各种映射函数模型的连分式之间，差别仅是形式上的，没有实质性差异。文章利用普尔科沃大气折射表的表列数据作模拟计算，求解折射率差和映射函数的参数证明，可以用天文大气折射定值作模拟处理，得到折射延迟改正模型中的所有参数，并得出结论：映射函数的形式是次要的，随着项数的增加，都能提高模拟精度。文章给出了模拟过程。