共查询到20条相似文献,搜索用时 15 毫秒
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M. A. Garrett R. W. Porcas A. Pedlar T. W. B. Muxlow S. T. Garrington 《New Astronomy Reviews》1999,43(8-10)
We discuss the technique of Wide-field imaging as it applies to Very Long Baseline Interferometry (VLBI). In the past VLBI data sets were usually averaged so severely that the field-of-view was typically restricted to regions extending a few hundred milliarcseconds from the phase centre of the field. Recent advances in data analysis techniques, together with increasing data storage capabilities, and enhanced computer processing power, now permit VLBI images to be made whose angular size represents a significant fraction of an individual antenna's primary beam. This technique has recently been successfully applied to several large separation gravitational lens systems, compact Supernova Remnants in the starburst galaxy M82, and two faint radio sources located within the same VLA FIRST field. It seems likely that other VLBI observing programmes might benefit from this wide-field approach to VLBI data analysis. With the raw sensitivity of global VLBI set to improve by a factor 4–5 over the coming few years, the number of sources that can be detected in a given field will rise considerably. In addition, a continued progression in VLBI's ability to image relatively faint and extended low brightness temperature features (such as hot-spots in large-scale astrophysical jets) is also to be expected. As VLBI sensitivity approaches the μJy level, a wide-field approach to data analysis becomes inevitable. 相似文献
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Martin A. Slade Robert A. Preston Alan W. Harris Lyle J. Skjerve Donovan J. Spitzmesser 《Earth, Moon, and Planets》1977,17(2):133-147
A program of ALSEP-Quasar Very Long Baseline Interferometry (VLBI) is being carried out at the Jet Propulsion Laboratory. These observations primarily employ a 4-antenna technique whereby simultaneous observations with two antennas at each end of an intercontinental baseline are used to derive the differential interferometric phase between a compact extragalactic radio source (usually a quasar) and a number of ALSEP transmitters on the lunar surface. A continuous ALSEP-quasar differential phase history over a few hour period will lead to milliarcsecond angular accuracy in measuring the lunar position against the quasar reference frame if suitable calibration measurements are obtained. Development of this application of the 4-antenna technique has been underway at JPL for more than a year and is now producing high quality data utilizing Deep Space Network (DSN) stations in Australia, Spain, and Goldstone, California as well as the STDN Apollo station at Goldstone. These high accuracy observations are of value to tie the lunar ephemeris to a nearly inertial extragalactic reference frame, to test gravitational theories, and to measure the Earth-Moon tidal friction interaction.This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS 7-100, sponsored by the National Aeronautics and Space Administration. 相似文献
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A. R. Whitney 《New Astronomy Reviews》1999,43(8-10)
Magnetic tape recording, disc recording, and global electronic networks are advancing rapidly, promising both evolutionary and revolutionary impacts on the way VLBI is conducted. In this paper, we will examine the state-of-the-art technologies that may have application to VLBI and consider the current and projected costs in each of these areas. 相似文献
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R. T. Schilizzi W. Aldrich B. Anderson A. Bos R. M. Campbell J. Canaris R. Cappallo J. L. Casse A. Cattani J. Goodman H. J. van Langevelde A. Maccafferri R. Millenaar R. G. Noble F. Olnon S. M. Parsley C. Phillips S. V. Pogrebenko D. Smythe A. Szomoru H. Verkouter A. R. Whitney 《Experimental Astronomy》2001,12(1):49-67
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空间VLBI的研究现状 总被引:2,自引:0,他引:2
评述了过去近三十年中空间VLBI的发展.其内容包括空间VLBI的简短发展历史,空间VLBI与地面VLBI的不同、空间VLBI的目前状况和空间VLBI的未来展望。着重介绍了作为首次空间VLBI的VSOP的各个方面情况,并给出了VSOP的连续谱、谱线普查样本,供参考。 相似文献
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《New Astronomy Reviews》1999,43(8-10):509-513
We present recent VLBI observations of HI and CO gas in AGN, emphasising the variety of phenomena probed by this technique. Broad (>100 km s−1) HI absorption in ellipticals appears to be commonly associated with circumnuclear gas in a TORUS (Thick Obscuration Required by Unified Schemes) at radii of 50–500 pc from the central engine. Examples include Cygnus A and the CSO 4C31.04. In both of these sources recent HST imaging appears to confirm the presence of a TORUS. However, not all broad absorption HI is TORUS related. In 3C 236, for instance, it seems to be due to a jet-cloud interaction. Narrow <100 km s−1 HI absorption lines also appear to be caused by a variety of different phenomena. For instance, VLBI observations show that the narrow, rapidly in-falling HI absorption gas in 4C31.04 is probably associated with High Velocity Clouds similar to those in-falling into our own Galaxy. In contrast, in 1413+135, the narrow HI and molecular absorption is probably due to a foreground molecular cloud in the host's galactic disk which fortuitously lies along the line of sight to the radio nucleus. 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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L.I. Matveenko 《Astronomische Nachrichten》2007,328(5):411-419
This article gives story of interferometer with independent elements (Very Long Baseline Interferometer) in Russia. At the end of February 1962 the author discussed with G.Ya. Gus'kov, DSN Station, Evpatorija a new type of radio interferometer and proposed an experiment between two DSN stations. In September 1962 he reported the new method and proposed a VLBI experiment at seminar of Radio Astronomical Laboratory, Pushino, and then at a seminar of Astronomical Institute GAISH which recommended to take out a Patent. In December GAISH sent documents to the Patent Bureau. In summer 1963 the author discussed with B. Lovell in Evpatorija the VLBI method of and we signed memorandum an Ev‐JB experiment at λ = 32 cm. In December 1963 the Patent Bureau permitted publication, and the paper was sent to Radiofizika. Really VLBI in the USSR began with the proposal of M. Cohen and K. Kellermann, February 1968, to do an experiment between 22‐m antenna Pushino and 43‐m Green Bank. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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J.-F. Desmurs 《Astrophysics and Space Science》2004,292(1-4):365-368
Magnetic field is believed to play an important role in the evolution of compact HII regions where massive stars are formed. In fact, it exists very few methods to measure it. One of the best method used, is based on the Zeeman effect: under the effect of the magnetic field, a line can be split into two separated lines of opposite circular polarization. The separation in frequency between the lines is directly proportional to the intensity of the magnetic field. One of the difficulty of the method, is to made a correct identification of the Zeeman pairs. The very high resolution achievable by VLBI allows us to demonstrate whether the pairs are spatially coincident (as expected in true Zeeman pairs) or not. The OH emission traces the densest pockets of the neutral gas environment. In addition, because of its non zero electronic angular momentum, the OH radical is a natural magnetometer allowing us to determine both the intensity and the direction of the magnetic field in the outer layers of the compact HII regions. In this poster I reported on the possibilities of VLBI observations of OH masers in the first excited state (J = 5/2) lying at 6 GHz. 相似文献
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K. F. Tapping 《Solar physics》1986,104(1):199-206
Very Long Baseline Interferometry offers the only technique for resolving the transient compact sources which, according to an increasing weight of observational and theoretical evidence, occur during solar flares. In this paper we discuss the problems of applying VLBI to observing the Sun, the results obtained so far and how the technique may be effectively employed in future studies of compact emission structures in solar flares.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
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VLBI标准接口是近年来在VLBI技术中诞生的一个新概念,它旨在解决多年来各VLBI数据传输系统不兼容的问题.该文阐述了VLBI数据传输系统的发展历史,包括传统的记录/回放系统和新兴的网络数据传输两方面的内容;说明了VLBI标准接口的作用和意义;并分别介绍了VLBI标准接口规范3方面的内容:VLBI标准接口件规范(VSI-H)、VLBI标准接口软件规范(VSI-S)和VLBI标准接口网络规范(VSI-E). 相似文献
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The first VLBI experiment between Shanghai and Effelsberg, West Germany, was carried out at 1430 MHz in November 1981. The observations lasted 54 hours and the Mark II recording system and hydrogen masers were used at both stations. Fourteen extragalactic sources covering a wide range of declination were duly observed. The Shanghai-Effelsberg baseline vector was determined to an estimated formal precision of 2–3 metres and the positions of the sources 1739 + 52 and 1928 + 73, to in each coordinate, with the effects of the ionosphere not removed. The source of 1928 + 73 was found to be double with a component separation of . 相似文献
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对VLBI(Very Long Baseline Interferometry)台站电磁兼容性的特点及其影响因素进行了分析;在对几种常用的评估方法对系统的适用性论证的基础上,借鉴网络层次分析法(ANP)中建模及求解权重的原理,结合理想点排序法(TOPSIS)的优点,并运用权系数确定的区间调整法降低主观因素的影响,提出一种适用于系统电磁兼容性的改进的ANP-TOPSIS综合评估方法;建立了系统网络层次评估模型;具有十分重要的理论及工程应用价值。 相似文献
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空间VLBI研究的现状和未来 总被引:4,自引:0,他引:4
空间VLBI卫星VSOP/HALCA是日本宇航科学研究所(ISAS)的飞行任务,已经在1997年2月升空。它拥有8m直径的射电望远镜,远地点达22000km。和地面的射电望远镜联合观测(干涉观测),其最高分辨率比地面VLBI提高了3倍。该项空间VLBI观测由NSAS的地面跟踪站支持。第一批VLBI图像已经在因特网上发表。RadioAstron项目由俄罗斯科学院列别捷夫物理研究所天文空间中心(ASC 相似文献