共查询到19条相似文献，搜索用时 46 毫秒
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天体测量学是天文学中最古老的分支之一, 它是天文学的基础, 对天体物理学和大地测量学的许多方面至关重要.天体测量学的核心任务之一就是建立一个高精度天文参考系, 以便利用这样的惯性参照系来描述天体的位置和运动、研究银河系的运动学特征及对同一天体在不同波段的对应体进行位置认证和比较.当前的天文参考系是参照银河系外天体(主要是活动星系核)的位置来定义的, 称为国际天球参考系(ICRS).在实测上, 与之相对应的基本星表为国际天球参考架(ICRF), 它由甚长基线干涉测量(VLBI)技术在S/X、K和X/Ka波段的观测资料解算而得, 位置精度达到数十微角秒($\mathrm{\mu as}$)水平.另一方面, Gaia卫星的观测也将在光学波段建立类似精度的光学参考架(Gaia-CRF).ICRF与Gaia-CRF的连接成为天体测量领域需要解决的重大问题之一, 这要求对ICRF与Gaia-CRF参考架特性进行细致深入的分析. 首先, 分析了ICRF的整体特性.VLBI星表的内部符合精度估计值在$\mathrm{10\mu as}$和$\mathrm{40\mu as}$之间, 依赖于射电源的观测次数.这一结果一方面验证了ICRF3星表给出的位置噪声水平, 也说明了VLBI技术在天体测量方面的潜力.利用Gaia的河外源位置为参考, 分析了历代ICRF星表的外部符合精度, 指出ICRF3 X/Ka波段参考架存在约$\mathrm{200\mu as}$的系统误差.最后, 发明了一种评估射电源全天分布均匀性的量化指标并改进了ICRF定义源筛选策略, 结果表明相较于ICRF2而言, 这一方法能将ICRF轴指向稳定性提高2至3倍.这些工作很好地解释并补充了国际上ICRF3工作组的相关结果. 其次, 研究Gaia-CRF的参考架性质.使用了相对于依巴谷参考架的全局旋转和结合银河系动力学分析两种方法来评估Gaia-CRF1的惯性水平, 指出Gaia-CRF1可能存在约$\mathrm{0.3mas\cdot yr^{-1}}$的剩余旋转.对于Gaia-CRF2, 研究了其系统精度与河外源样本极限星等的依赖关系, 发现Gaia-CRF2的整体精度几乎不受星等差的影响.这一结果可作为未来ICRF与Gaia-CRF连接源选择的参考. 活动星系核的光学-射电位置差是影响参考架连接精度的重要因素之一.本文首次将光学-射电位置差研究延伸到K和Ka波段, 并研究其与河外源性质参数的相关性, 发现: 光学-射电位置差与星等的相关性是由于星等差而非真实的物理原因造成的, 因此在前人工作中被忽略的暗源也有可能作为ICRF与Gaia-CRF连接源.此外, 本文提出了一种新的参考架连接方法, 即在Gaia-CRF2框架下重新处理VLBI的历史观测资料.先期结果发现使用Gaia-CRF2来替代ICRF3尚不足以显著提高VLBI产品的精度, 但未来在Gaia-CRF参考架精度进一步提高后, 此方法仍值得进一步检验. 本文的研究, 一方面指出了ICRF与Gaia-CRF参考架中可能存在的种种问题, 另一方面也为将来光学与射电参考架连接提供了第一手的参考资料. 相似文献
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第三代国际天球参考架(the 3rd realization of the International Celestial Reference Frame, ICRF3)于2019年1月1日起,代替其前代参考架第二代国际天球参考架(the 2nd realization of the International Celestial Reference Frame, ICRF2)成为最新的国际天球参考架,与国际天球参考系(the International Celestial Reference System, ICRS)在ICRF2的误差范围内指向一致。ICRF3发表后,在诸多领域中都发挥着至关重要的作用。ICRF3的新特点也给其数据的使用带来了影响。详细介绍ICRF3的基本性质,并对ICRF3的使用方法进行说明,还将ICRF3内部三个波段参考架,以及ICRF3与Gaia-CRF3进行了比较,检验了ICRF3参考架的稳定性,讨论了其中可能存在的系统误差。 相似文献
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目前利用VLBIMK3系统确定的延迟测量的精度约为30ps,在这样的精度下,改善计算延迟的理论模型,考虑各种微扰改正（包含30ps量级）是非常重要的。在VLBI天休测量和测地计算的各种软件中,至今尚未计及射电源结构对延迟的影响。本文利用两子源模型对源结构延迟的大小及随时间的变化进行了计算,讨论了源结构延迟对VLBI天测和测地参数的影响,指出：（1）除对某些VLBI天测的射电源作长期的监测与研究,给出它们的双频综合图外,对大多数源可采用简单的两子源模型;（2）源结构对延迟的影响主要依赖于基线相对于源形态的主要特征的空间投影;（3）源结构延迟对天测和测地参数的影响达厘米和亚毫角秒量级。 相似文献
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通过比较地球定向参数（EOP）序列和对应的地因参考架，得到了依巴谷输入星表（HIC）和临时星表H37与国际地球自转服务（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，HIC和H37至ICRF的旋转分别为[7．4±1．1mas，70．0±1．2mas，86．8±6.9mas]和[－27.4±1.0mas，10.4±1．0mas，70．3±4．6mas]。由于光学仪器位置坐标精度较低，第三个旋转角的可信度较差。 相似文献
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卫星双向时间比对及其误差分析 总被引：26，自引：0，他引：26
介绍了卫星双向时间比对(TwsTT)方法的发展过程及其基本原理，讨论了TwsTT的误差源，分析了各误差源对比对精度的影响。得出影响TwSTT精度的主要误差源为设备时延误差和路径传播时延误差，而由于卫星和地面站运动引起的误差相对较小，从而给出了实际应用时不同比对精度下需要考虑的误差源及对误差源的精度要求。 相似文献
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介绍了差分VLBI技术确定空间飞行器位置的原理。在上海、乌鲁木齐和昆明站开展了对地球同步卫星的首次国内差分VLBI观测 ,实验中选择 3颗角距小于 15°的ICRF射电源作为参考源 ,克服了卫星观测的特殊性带来的困难 ,成功地获得了卫星信号的干涉条纹。基于条纹拟合的结果和系统差分析 ,估计双差单向测距的总误差约为 4 1cm ,双差单向测速的总误差约为 0 .14 8mm/s,相当于在地球同步轨道上 8m的位置误差和 2 .8mm/s的速度误差 相似文献
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《天文学进展》2018,(4)
为了提高甚长基线阵列(very long baseline array, VLBA)校准射电源位置的精度,建立新一代的国际天球参考架(international celestial reference frame, ICRF),VLBA开展了第二个历元校准源巡天观测(VLBA calibrator survey Ⅱ, VCS-Ⅱ)。BG219I是其中第8组观测,共有298颗射电源在S和X双波段被成功检测到,其中48颗是首次被检测到的射电源。给出了这298颗射电源的成图结果,并根据它们的亮度分布,用δ函数分量建模,计算出这些射电源的结构时延和结构指数。研究了致密度跟结构指数的关系,发现结构指数越小的射电源,具有越大的致密度。还统计了21颗谱指数小于-0.8的陡谱射电源,发现它们在单个波段或者两个波段的结构指数均超过3.0,表明这些射电源不够致密,因而不适合高精度的天体测量。最后,研究了射电源的位置精度与结构指数的关系,发现射电源的位置精度随着结构指数的变大而逐渐降低。 相似文献
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无源电视同步已用于天文台和时辰站主钟之间的时刻比对。电视同步的精度和准确度是适中的。本文初步分析了无源电视同步记录的实验数据,表明时刻同步精度可以与罗兰—C 方法相比拟。 相似文献
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Gérard Daigne Patrick Charlot Christine Ducourant Jean-François Lestrade 《Astrophysics and Space Science》2003,286(1-2):255-260
The question of positioning the optical counterparts of the ICRF quasars is outlined in the perspective of future space astrometry
missions, which ultimately will bring a new realization of the ICRS in the optical range. Ground-based interferometry with
a dual-field observing mode (PRIMA/VLTI),together with the missions DIVA and FAME, will have a key role in building an extragalactic
reference frame in the optical/near-IR range with about the same accuracy as that of the present (VLBI) primary frame.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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V. P. Ryl’kov N. V. Narizhnaya A. A. Dement’eva G. I. Pinigin N. V. Maigurova M. V. Martynov 《Kinematics and Physics of Celestial Bodies》2011,27(6):299-303
A compiled catalogue of 21 440 stars with magnitudes between 10 and 17 is prepared from original observations made at the end of the 20th century to the beginning of the 21st century. The catalogue contains 227 fields of the celestial sphere centered at ICRF extragalactic radio sources with declinations of ?17 to +89°. The field size is 40′ for both right ascension and declination. The internal accuracy of positions for both coordinates is no worse than 0.1″. A comparison of the stellar positions with the UCAC2 and CMC13 catalogues shows that the average external accuracy is approximately 0.05–0.15″. The positions of 10 795 stars with declinations to +50° are given for the epoch and equinox of J2000.0, whereas the positions of other stars are given for the epoch of observation. 相似文献
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Solar System Research - Finding and studying possible collisions of asteroids approaching the Earth requires a significant amount of computation. This paper describes the R0 program created to... 相似文献
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Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF31, were discovered, librating about the L5 Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ7, to be a Trojan, associated with the L4 Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND43) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW15 and 2000 TG2, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion. 相似文献
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In the text-books of astronomy, sections generally related to the Moon deal with the orbital elements of the Earth-Moon system such asa, e, i, ,
and the time of perigee passage. While the MEAN of the first of the three elements do not vary, mean longitude of the ascending node-mean longitude of the lunar perigee and the time of perigee passage undergoes secular as well as periodic changes due predominantly to the action of the Sun's gravitational attraction. While to a certain degree, explanations related to the calculation of the lunar orbit parameters are given, not a single graphical representation of these short- or long-periodic changes are presented. We allow the number of data related to these periodic changes must cover a large span of time; and if regression of the line of nodes or advances of the line of apses are to be graphically seen, data covering 18.61 and 8.85 yr, respectively, are needed. In this work we particularly aim at the graphical representation of the periodic changes of the line of nodes. 相似文献
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Magnetars are the neutron stars with the highest magnetic fields up to 1015–1016 G. It has been proposed that they are also responsible for a variety of extra-galactic phenomena, ranging from giant flares in nearby galaxies to fast radio bursts. Utilizing a relativistic mean field model and a variable magnetic field configuration, we investigate the effects of strong magnetic fields on the equation of state and anisotropy of pressure of magnetars. It is found that the mass and radius of low-mass magnetars are weakly enhanced under the action of the strong magnetic field, and the anisotropy of pressure can be ignored. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars. 相似文献