无人值守GNSS方法测定射电望远镜参考点

为解决常规射电望远镜归心测量工作耗时耗力的问题,引入GNSS (Global Navigation Satellite System)同步监测技术实现了一种针对射电望远镜参考点的无人值守监测方法.设计了针对GNSS靶标点观测数据的归算方法,包括数据匹配、数据检核以及后续精度评估等步骤,并对2018年佘山25-m射电VLBI (Very Long Baseline Interferometry)望远镜的GNSS靶标点实测数据开展了数据预处理、解析与归心解算等,证明了该方法的可行性.结果表明基于该方法,采用单日内部分(5%)数据(约7600个靶标点),所测定的VLBI望远镜参考点的点位形式精度可达3 mm.总结了针对射电望远镜采用GNSS开展无人值守归心测量先行试验中的一些经验教训,明确了利用该方法测量过程中应该注意的问题,为今后更高精度射电望远镜参考点无人值守归心监测提供重要参考.     

IVS分析中心EOP产品及精度评估

介绍了国际测地/天体测量学甚长基线干涉测量服务(International Very Long Baseline Interferometry (VLBI) Service for Geodesy and Astrometry, IVS)组织机构及下属分析中心概况.系统归纳了目前IVS发布的地球定向参数(Earth Orientation Parameters, EOP)产品类型及不同观测类型的用途.利用2010—2019年公开发布的观测资料,对IVS不同分析中心的EOP日常监测和服务能力进行了评估.通过构造观测台站所构成的几何体积,分析了EOP精度与测站数量、测站网分布的关系,统计了IVS不同观测类型的EOP解算精度.此外,综合公开发布的美国、欧洲等区域网观测数据,分析了不同地区区域网的常规及加强观测结果与IVS结果的差异.结果表明:EOP的解算精度与观测台站的分布密切相关, IVS常规观测确定的极移分量的外符合精度优于0.2 mas,世界时(Universal Time, UT1)与协调世界时(Coordinated Universal Time,UTC)之差(UT1-UTC)的精度在0.015 ms左右,加强观测的UT1-UTC值与国际自转服务组织(International Earth Rotation Service, IERS)的C04之间存在0.02–0.03 ms的差异.区域观测网的精度受观测网形和基线长度制约,总体劣于IVS观测精度,其中,美国甚长基线干涉阵列(Very Long Baseline Array, VLBA)的常规及加强观测结果与IVS全球观测结果最接近.     

天王星5颗主要卫星CCD定位观测试验

使用云南天文台1 m望远镜连续4个夜晚观测得到的248幅CCD图像对天王星5颗主要卫星(Ariel、Umbriel、Titania、Oberon和Miranda)进行了精确的位置测量.在位置归算过程中,采用了最新发布的Gaia DR1(Data Release 1)作为参考星表,并将卫星的观测值和理论计算值作比较.卫星的理论位置参考JPL(Jet Propulsion Laboratory)历表(其中天王星理论位置参考了DE431行星历表).结果显示:5颗卫星在赤经和赤纬方向的O-C平均值(观测值-理论值)均不超过0.027′′(天卫一Ariel:0.027′′和-0.007′′;天卫二Umbriel:0.024′′和-0.003′′;天卫三Titania:0.021′′和0.020′′;天卫四Oberon:0.024′′和-0.001′′;天卫五Miranda:0.021′′和0.001′′).前4颗卫星两个方向的测量精度均好于0.015′′,Miranda的精度可达到0.030′′.     

利用GPS数据标校水汽辐射计的方法研究

对流层是影响各类对地观测、地对空观测精度的主要因素之一.目前GNSS(Global Navigation Satellite System)技术由于其时空分辨率和精度方面的优越性,成为大气延迟和水汽监测的主要手段之一.水汽辐射计WVR (Water Vapor Radiometer)是传统的大气探测手段,由于其观测原理和灵敏度等方面的特点,也有其特殊的用途. WVR在正式投入使用前必须根据各个测站的具体情况进行标校,一般采用探空数据来进行,但探空数据采样频率低、数据量小, GNSS具有相对的优势.利用分布于北京(BJMY)、上海(SHAO)、昆明(YNKM)、乌鲁木齐(URUM) 4个VLBI (Very Long Baseline Interferometry)台站的GPS和水汽辐射计数据,开展了利用GPS数据标校WVR的方法研究,探讨了各个台站WVR的数据预处理方法,分析了影响水汽辐射计测量精度的因素.利用2015–2016年的4个并置台站的GPS和WVR观测数据,验证水汽辐射计数据的稳定性与可靠性.采用归一化处理方法,利用GPS数据对水汽辐射计进行了校准,为水汽辐射计的标校提供了一种新的思路和方法.     

多种空间大地测量技术内综合方法研究及精度分析

详细地叙述了国际空间大地测量技术服务组织ILRS(International Laser Ranging Service),IVS(International VLBI Service),IGS(International GNSS Service)和IDS(International DORIS Service)分别采用SLR(satellite laser ranging),VLBI(very long baseline interferometry),GPS(global positioning system)和DORIS(Doppler orbitography and radio-positioning intergrated by satellite)四种技术,并由多家分析中心的站坐标和地球定向参数的SINEX(solution in independent exchange format)周解(或24 h观测解)进行技术内综合解算的方法,包括技术内综合模型的建立、参考架基准约束问题和不同分析中心解的定权方法等主要内容,并对ILRS,IVS,IGS和IDS提供的技术内综合周(日)解的长期序列进行了站坐标和地球定向参数(earth orientation parameters,EOP)的精度评估,分析了地球参考架基准参数的长期特性。由地球参考架基准定义可知,SLR技术内SINEX综合解相对于ITRF2014的平移参数时间跨度最长,且没有明显的偏差或漂移;GPS技术的三个方向平移参数虽然弥散度最低,但是在X方向和Y方向存在长期的线性变化,在Z方向存在跳变;DORIS技术也有类似GPS技术的现象。这些结果说明ITRF2014选择SLR定义的地心作为参考架原点是有道理的。通过分析台站坐标精度可知,利用各种技术对核心站和非核心站进行区分非常重要,所分别得到的精度有明显的不同。由于GNSS(global navigation satellite system)台站多且分布广,因此地球定向参数的确定精度要高于其他三种技术。     

上海天文台VLBI，SLR和GPS站的归心结果与分析

本文重新处理了最近几年来利用GPS技术测定上海天文台GPS站坐标的资料，给出了GPS站相对于VLBI，SLR站的基线矢量，并与利用常规方法归心的最新结果进行了比较和,是到了IGS‘92联测中上海天文台GPS技术解算的SH01站坐标，与VLBI技术解算的结果比较，两者相差小于2.6cm，同时得到GPS技术归心的符精度好于1cm。     

用激光测月资料检测板块运动初探

本文讨论了用现有激光测月资料检测板块运动的可能性。用多站资料,通过解算基线变化来研究板块运动。由于激光测月网形成时间不久,共同观测时段的资料积累不多,凭现有资料尚不足以研究这一问题。利用单站资料解算地球自转参数中的(UT1—UTC),并将各站所得的序列同BIH(国际时间局)的综合解序列(1988年为IERS—国际地球自转服务的结果)相比较,间接地检测台站的经度方向运动,精度在厘米量级,与AM_(1-2)模型的预测值符合得较好。     

中国SLR区域网定轨精度的分析

该文利用中国SLR网的实测资料,以SHORDE软件独立解算卫星的轨道和地球定向参数(EOP),并与全球SLR网解算的结果进行了比较。结果表明:中国SLR网30天弧段观测拟合轨道的中误差优于2cm。与全球SLR网解算结果相比,定轨的位置精度可优于50cm;5天弧段测定EOP的精度,Xp、Yp可优于5mas,Dr优于0.2ms。     

利用IVS加强观测确定UT1的分析研究

首先对IVS(International VLBI Service for Astrometry and Geodesy)UT1加强观测的历史发展和总体情况进行了比较详细的介绍,对目前加强观测中存在的问题进行了比较全面的分析;在此基础上对IVS从1984年2月到2011年8月全部的加强观测数据进行了综合处理,进一步分析了加强观测解算UT1的历史改进和目前的解算能力,对比分析不同类型加强观测的UT1结果,发现不同观测网之间存在数十微秒水平的差异;并着重分析了上海佘山站参与的加强观测的解算结果,分析表明上海佘山站在IVS加强观测中与其他参与台站具有相同的测量能力.总体而言,目前IVS加强观测确定的UT1与IERS(International Earth Rotaion Service)C04之间存在约10μs水平的不确定性.     

姿态卡尔曼滤波对FAST馈源舱 BDS/SINS组合导航位姿精度的提高

500 m球面射电望远镜(The Five-hundred-meter Aperture Spherical radio Telescope, FAST)馈源舱位置和姿态测量精度直接影响望远镜接收机的对准精度.为了提高馈源舱位姿精度,提出姿态卡尔曼滤波算法,采用北斗导航系统的多天线技术解算馈源舱姿态,将它与捷联惯导解算的馈源舱姿态对比,两者的差值作为姿态卡尔曼滤波的量测量.为了降低北斗导航系统解算姿态的复杂度,采用了罗德里格矩阵解算方法.以望远镜跟踪观测模式时,北斗导航系统和捷联惯导解算的实际导航结果作为测试数据,测试结果表明采用姿态卡尔曼滤波的组合导航结果精度优于传统卡尔曼滤波的组合导航结果,尤其在航向角和yf轴的位置精度上.     

Composite spectra XIX: HD 208253, a long‐period binary whose hot secondary has enhanced strontium and barium

We separate and analyse the component spectra of the composite‐spectrum binary HD 208253. We find that the cool primary is an evolving star of spectral type G7 III, while its hot secondary is an early‐A dwarf. The giant is currently near the lowest point of the red‐giant branch and is slightly less luminous than its dwarf companion. We provide a set of precise radial‐velocity measurements for both stars. The double‐lined orbit which we derive from them shows that the component mass ratio is close to unity (q = 1.05 ± 0.01). We deduce the physical properties of both stars, determine their respective masses to be 2.75 ± 0.07 Me (giant) and 2.62 ± 0.07 Me (dwarf), and show that the orbit's inclination is within a degree or two of 68°. The spectrum of the A‐type component has quite component has quite narrow lines (we infer a rotational velocity of 18 km s^–1), though since the period of the orbit is well over 1 year that component cannot be in synchronous rotation. An intriguing property of the dwarf is its enhanced Sr and Ba, though it does not exhibit the other spectral peculiarities that would signal a classical Am star. While by no means unique amongst the multitude of oddities exhibited by A and early‐F stars, this dwarf which we have uncovered in a long‐period binary offers valuable constraints and challenges to stellar‐evolution theory. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

导航卫星精密定轨与时间同步技术进展

全球卫星导航系统(Global Navigation Satellite System, GNSS)通过播发卫星钟差和精密轨道信息实现时间和空间基准信息向导航用户的传递.随着高精度原子钟等导航卫星载荷、星间链路等天基/地基监测手段以及数据处理方法等技术的不断更新,卫星轨道和钟差产品的精度和实时性也逐步提升. 2018年12月,北斗三号卫星导航系统正式开通,为"一带一路"国家提供实时高精度、高可靠的基本导航定位服务.综述了北斗导航系统从北斗二号区域系统到北斗三号全球系统精密定轨与时间同步处理面临的困难和挑战,针对上述问题,阐述了北斗运行控制系统的解决途径和实现指标.与GPS等其他GNSS系统进行比较,分析了不同导航系统技术特点.最后展望了精密定轨与时间同步技术未来的发展路线图,为更高精度的GNSS导航定位授时服务提供参考.     

上海天文台新SLR站精密定位和归心测量

为使上海天文台新SLR站尽早投入全球SLR网的运行,根据中国SLR网的有关要求,对该站进行了精密定位和归心测量。测量中安置了特制的对中滑块设备,在小范围内采用三角测量的高差替代大地高差的近似,取得了较好的效果。测量结果表明:上海天文台新SLR站相对于上海IGS站归心测量精度可优于5 mm,由上海IGS站引得的点位精度可优于10 mm。     

Hansen系数及其导数的直接计算方法

回顾总结了7种Hansen系数及其导数的直接计算方法,比较分析了这些方法的计算效率和计算稳定性.研究表明:Hansen系数的递推关系可以用来判别计算结果的稳定性.最后指出, Wnuk方法(双精度计算)和McClain方法(4精度计算)是稳定的,可以用来计算人造卫星轨道摄动.由于大多数人造卫星采用小偏心率轨道,需要计算无奇点摄动,推荐使用McClain方法1 (4精度计算).     

A uvbyβ photometric analysis of the Monoceros star‐forming field

This investigation presents a new analysis of the spatial distribution of the bright early‐type stars in the field of Northern Monoceros. A database of all O–B9 stars with available uvbyβ photometry is collated and a homogeneous distance scale is established for the clusters and layers of field stars. We provide revised distances for NGC 2264 and NGC 2244 of 833±38 (s.e.) pc and 1585±60 (s.e.) pc, respectively. We present arguments that there might be substructures in the clusters projected along the line of sight. According to the present sample the classical Mon OB2 association at 1.6 kpc is represented by a relatively compact group at 1.26 kpc in the vicinity of NGC 2244 and a layer of massive stars located between 1.5 and 3 kpc (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tropospheric Delay from VLBI and GNSS Measurements

Using an updated version of the QUASAR software package developed at the Institute of Applied Astronomy of the Russian Academy of Sciences, we have processed the VLBI observations within the international CONT14 program (May 6–20, 2014), in which a global network of 17 stations was involved (a total of ~250 000 observations). The package update concerned the optimization of data structure and the refinement of stochastic models for the random variations in wet tropospheric delay and atomic clock difference. The main goal of this paper is to compare the VLBI determinations of the tropospheric delay with its independent determinations using global navigation satellite systems (GNSS). We show that both these determinations agree well between themselves only in the case of a global analysis of the VLBI observations, where the VLBI station coordinates are also refined, along with the tropospheric delay and the clock synchronization and Earth orientation parameters. If, alternatively, the station coordinates are insufficiently accurate and are not refined from VLBI observations, then it is appropriate not to determine the tropospheric delay from these observations, but to take it from the publicly accessible independent GNSS data. However, this requires that the VLBI and GNSS techniques operate simultaneously at a common observing site. We have established the shortcomings of the universally accepted method of stabilizing the global solution associated with the absence of a criterion for choosing reference stations and radio sources. Two ways of their elimination are proposed: (i) introducing a coordinated list of weight factors for the errors in the coordinates of such stations and sources into the stabilization algorithm and (ii) adopting a coordinated list of stations and sources the refinement of whose coordinates is not required at all for a certain time.     

Weekly inter-technique combination of SLR,VLBI,GPS and DORIS at the solution level

Constructing and maintaining a stable terrestrial reference frame(TRF) is one of the key objectives of fundamental astronomy and geodesy. The datum realization for all the global TRF versions,such as ITRF2014 and its predecessor ITRF2008, assumes linear time evolution for transformation parameters and then imposes some conditions on these Helmert transformation parameters. In this paper,we investigate a new approach, which is based on weekly estimation of station positions and Helmert transformation parameters from a combination of the solutions of four space-geodetic techniques, i.e.,Satellite Laser Ranging(SLR), Very Long Baseline Interferometry(VLBI), Global Positioning System(GPS) and Doppler Orbitography and Radiopositioning Integrated by Satellite(DORIS). For this study,an interval of one week is chosen because the arc length of the SLR solutions is seven days. The major advantage of this weekly estimated reference frame is that both the non-linear station motions and the non-linear origin motion are implicitly taken into account. In order to study the non-linear behavior of station motions and physical parameters, ITRF2008 is used as a reference. As for datum definition of weekly reference frame, on one hand SLR is the unique technique to realize the origin and determine the scale together with VLBI, and on the other hand the orientation is realized via no net rotation with respect to ITRF2005 on a subset of core stations. Given the fact that without enough collocations an inter-technique combined TRF could not exist, the selection and relative weight of local ties surveyed at co-location sites are critical issues. To get stable results, we first assume that, if there were no events such as equipment changes between the measurement epoch of the local tie and that of the spacegeodetic solution, the relative position between the two co-located stations should be invariant and this local tie could be used for computing the inter-technique combined reference frame in those weeks during the stable period of this tie. The resulting time series of both station positions and transformation parameters are studied in detail and are compared with ITRF2008. The residual station positions in the weekly combined reference frame are usually in the range of two millimeters without any periodic characteristic, but the residual station positions, when subtracting the regularized station position in ITRF2008, may reach a magnitude of a few centimeters and seem to have a significant annual signal.The physical parameter series between the weekly reference frame and ITRF2008 also show the obvious existence of an annual signal and reach a magnitude of one centimeter for origin motion and two parts per billion(ppb) for scale.     

The young open cluster Trumpler 3

We present a photometric and spectroscopic study of the poorly investigated open cluster Trumpler 3. Basic parameters such as the age of 70 ± 10 Myr, the color excess E (B – V) = 0.30 ± 0.02 mag, the distance of 0.69 ± 0.03 kpc and the limiting radius of 12′ were redetermined and compared with previous preliminary studies. The distance of 0.65 ± 0.09 kpc was determined independently by spectral parallaxes. Simultaneously, our analysis allowed us to estimate a total number of members to be N_tot = 570 ± 90 and a total mass of the cluster to be M_tot = 270 ± 40 M_⊙. We also determined a state of cluster's dynamical evolution. We conclude that Trumpler 3 is a young low‐massive stellar ensemble with a typical mass function slope, located near to the outer edge of the Galaxy's Orion Spur. As a result of a wide‐field search for short period variable stars, 24 variables were discovered in the cluster's area. Only one of them – a variable of the γ ‐Dor type – was found to be a likely cluster member (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)