共查询到20条相似文献，搜索用时 31 毫秒
1.
Zhi-qiang Shen Tong-shan Wan Xiao-yu Hong Dong-rong Jiang Shi-guang Liang 《Chinese Astronomy and Astrophysics》1996,20(4):415-425
This paper describes a 5 GHz VLBI survey in the southern hemisphere. The first observation of 23 extragalactic radio sources was conducted in November 1992. Twenty VLBI images were obtained, of which 15 sources show core-jet structure, one has a two-sided jet, and three sources are unresolved. No compact double source was found. Eleven of the 16 sources with core-jet (including a two-aided jet) show evidence of jet bending. In addition, four sources appear to be superluminal, of which three sources are new. 相似文献
2.
本文报道南天区5GHzVLBI普查式观测结果．首次观测是在1992年11月期间进行的，共观测了23个河外射电源，获得了20个河外射电源的VLBI高分辨率的射电图象．有15个射电源呈现核喷流结构，1个有双向喷流，3个未分解，末发现有致密观源．在16个核喷流（包括一个双向喷流源）源中有11个呈现弯曲喷流现象．此外还首次发现有3个源中可能有超光速运动现象． 相似文献
3.
The spectroscopic red shifts of seven optical objects whose coordinates coincide with those of radio sources in the IVS (International
VLBI Service for Geodesy and Astrometry) program list are determined from observations with the 6-m BTA telescope at the Special
Astrophysical Observatory (SAO) of the Russian Academy of Sciences. A comparison of these spectra and red shifts with data
in the radio frequency range shows that four of the objects discussed here are correctly identified, while the other three
require further study. The distances to the radio sources derived from our measurements yield more accurate estimates of the
cosmological model parameters than those based on the proper motions of these objects derived from geodesic VLBI observations. 相似文献
4.
空间VLBI与天文地球动力学 总被引：5，自引：0，他引：5
介绍了空间VLBI的精密定轨及其在天文地球动力学应用研究中的最新进展．指出因为空间VLBI的时延和时延率观测量同时涉及到射电参考系、动力学参考系和地固参考系,所以特别适合于参考系的直接连接工作．对为评价参考系连接的精度而发展的协方差分析理论也作了介绍,还分析了将时延和时延率资料用于精密定轨时遇到的困难及其解决办法． 相似文献
5.
A. E. Volvach V. I. Kostenko M. G. Larionov L. N. Volvach D. M. Mucha A. S. Nabatov A. M. Reznichenko 《Bulletin of the Crimean Astrophysical Observatory》2012,108(1):158-162
As part of the scientific cooperation between Ukraine and Russia, a series of studies on the preparation of the ground segment of the RadioAstron mission has been carried out. A scientific program of measurements to be performed using the 22-m RT-22 radio telescope (Crimean Astrophysical Observatory) has been prepared. A substantial part of this program is the study of compact structures in extragalactic sources. Ground-based VLBI test experiments at 6 and 18 cm intended for testing a model of the ground segments of the RadioAstron mission have been carried out at RT-22 of the Crimean Astrophysical Observatory in Simeiz and RT-70 (P-2500) in Evpatoriya. The processing of the data recorded by each antenna resulted in obtaining and calibrating responses of cross-correlation functions using the ASC LPI correlator. The results of the experiment demonstrate the readiness of RT-22 and RT-70 to participate in the ground-space radio interferometer sessions in the RadioAstron mission. 相似文献
6.
Space VLBI is a new observing technique which will be available in the second half of this decade by radio telescopes as interferometer elements in orbit. Besides the main astronomical interests, this new development has some very interesting potential applications in satellite dynamics, geodesy and geodynamical research which qualify space VLBI a potential new technique in space geodesy. A geodesy demostration experiment (GEDEX) is being proposed for the Japanese space VLBI satellite-VSOP, with the main objectives of reference frame interconnections and orbit accuracy improvement of the space radio telescope. The paper gives a review of the special characteristics of space VLBI and a general background of the GEDEX proposal. 相似文献
7.
The results of observations of 46 radio stars carried out with the Repsold meridian circle of the Kyyiv University Observatory in 1984–1985 and 1989–1991 are presented. The main goal of these observations is to improve the optical positions of radio stars for determination of a relationship between the optical and VLBI reference frames. The standard errors of averaged positions in two catalogues amount to 0.2 arcsec. These results were compared with those obtained with the Bordeaux meridian circle. 相似文献
8.
ＴｈｅＹａｌｅ／ＳａｎＪｕａｎ南天自行计划简ＳＰＭ。ＳＰＭ是美国里克天文台北天自行计划在南天的延伸。根据ＳＰＭ计划，最终在南天相对的星系测定出大约一百万颗天体的绝对自行、位置、星等和颜色。ＳＰＭ最初目的是研究角河系结构。 相似文献
9.
本文简述了国际天球参考架的发展历史和现在射电参考架的现状—基准源选择的标准和参考架的稳定性。描述了地面上光学观测在依巴谷参考架的维持和加密的一系列工作。介绍由天体测量卫星GAIA和SIM给出的天球参考架可能逵到的精度。详述了在今后十年中地面天体测量的作用以及正在开展有关天球参考架的研究课题 ,同时也列出了我国正在和即将开展天体测量的几个研究课题 相似文献
10.
O. A. Titov 《Astronomy Letters》2007,33(7):481-487
According to the most recent geodetic VLBI data, some of the radio sources that define the fundamental celestial reference frame are astrometrically unstable. In contrast to the stellar proper motions described by a linear function, the apparent proper motions of quasars are more complex. Therefore, they are difficult to approximate by a particular model. Being disregarded, the positional instability of the defining quasars can lead to a bias in the estimates of other parameters from observations, for example, the nutation angle corrections. 相似文献
11.
The distribution of systematic errors in the coordinates of 1217 extragalactic radio sources included in the latest version of the ICRF2 (International Celestial Reference Frame) reference catalog has been mapped for the first time by processing VLBI observations from international astrometric and geodetic programs spanning the period 1980–2012. These errors are shown to reach ±1.0 mas (milliarcseconds). However, for a sample of 752 sources observed more than 100 times, these errors do not exceed ±0.2 mas, suggesting that ICRF2 is inhomogeneous. In addition, the individual stability of dozens of extragalactic radio sources and ground-based stations included in the latest version of the International Terrestrial Reference Frame, ITRF2005, has been investigated. Significant linear trends and anomalous shifts reaching ±20 µas (microarcseconds) have been detected for many of the sources. Significant systematic shifts have also been found for some of the reference stations. The results obtained stimulate a search for new methods of analyzing VLBI observations and ways of their global adjustment that would provide greater homogeneity and stability of the ICRF and ITRF. This is needed both to increase the accuracy of determining the astrometric, geodetic, and geodynamic parameters derived from these observations and to facilitate their physical interpretation. The work has been performed with the QUASAR multifunction software package developed at the Institute of Applied Astronomy of the Russian Academy of Sciences. 相似文献
12.
S. J. Tingay R. A. Preston B. G. Piner M. L. Lister D. L. Jones D. W. Murphy T. J. Pearson A. C. S. Readhead H. Hirabayashi H. Kobayashi M. Inoue 《New Astronomy Reviews》1999,43(8-10)
The VSOP Space VLBI mission uses the HALCA spacecraft, launched from Japan in February 1997, in conjunction with ground radio observatories around the world to create a high resolution radio-wavelength imaging facility. We are using this unique facility to observe a sub-sample of Pearson-Readhead Survey sources at 4.8 GHz to determine core brightness temperatures and pc-scale jet properties. We will highlight one of the sources that has been observed using a combination of the HALCA spacecraft and the EVN, 1642+690, and describe the preliminary brightness temperature distribution for the sub-sample, based on all data analyzed to date. 相似文献
13.
1979-1999全球天测与测地VLBI观测资料处理结果与讨论 总被引：1，自引：0，他引：1
采用国际地民服务（ＩＥＲＳ）１９９６年规范和上海天文台甚长基线干涉测量（ＶＬＢＩ）资料分析软件,对自１９７９年８月以来全球约２９００次天测与测地ＶＩＢＬ实验进行了综合归算,得到６０１颗河外射电源在Ｊ２０００．０的坐标、１０１台站在Ｊ１９９７．０的坐标和运动速度、以及约２０年地地球定向参数序列。与国际相关结果的比较表明,归算结果不存在显著系统差。通过对归算结果的分析,指出目前国际上评估天球参考架局部 相似文献
14.
Using a new version of the QUASAR domestic multifunction software package, we have simultaneously processed all of the available
VLBI observations performed on global networks of stations over the period 1979–2009. New improved and extended versions of
the international reference systems of coordinates of extragalactic radio sources and ground-based VLBI stations and a new
independent series of Earth orientation parameters have been obtained. Analysis of the accuracy of these results shows that
they are at the level of the best determinations at national and international VLBI data analysis centers. 相似文献
15.
由于遥远的天体发出的无线电信号极其微弱,信噪比极低,VLBI系统要想得到较高的测量精度,必须尽量加大测量带宽和提高采样位数,但是这样会导致VLBI终端(比如数字基带转换器)产生的观测数据激增。传统的VLBI终端数据传输系统采用VSI接口,数据最高传输速率限制在2 Gbps,且数据记录设备必须采用定制的Mark5B设备,极其不灵活,因此已经不能适应现在VLBI系统的观测需求。为了提高数据传输速率,增加数据记录设备的灵活性,上海天文台新研制的基于多相滤波器组和快速傅里叶变换方式的数字基带转换器的数据传输系统采用了高速灵活的10 G网络接口。10 G网络系统中数据传输采用报文交换方式,因此数据到达接收端的时间不是精确可靠的,这要求数据在进入10 G网络接口之前必须已经具有标准的VLBI数据格式,所以在10 G网络前端设计了Mark5B格式器。详细介绍了基于现场可编程门阵列的Mark5B格式器及10 G网络传输系统的设计原理,并在文章的最后通过三组实验验证了其功能的正确性和性能的稳定性。 相似文献
16.
Several recent global and Space VLBI surveys of quasars, Active Galactic Nuclei of other types and star-burst galaxies provide a wealth of material on milli- and sub-milliarcsecond radio structures in hundreds of sources. Results of these projects are presented with an emphasis on the statistics of redshift- and angular-scale-dependent properties of the milli- and sub-milliarcsecond radio structures. These studies make possible disentanglement of intrinsic (possibly, evolutionary) phenomena of parsec-scale radio structures and the imprints of the cosmological model. The studies indicate a very promising potential of high-resolution applications of the Square Kilometer Array. Based on our pilot projects we estimate that a sample containing of the order of 104 faint radio sources in the luminosity range 1022–1026 W/Hz can be surveyed by a high-resolution SKA with the milliarcsecond resolution at cm wavelengths. Such the high resolution radio survey, including those conducted jointly by SKA and Space VLBI missions, in conjunction with data from other domains, will provide a new ground for extragalactic studies. 相似文献
17.
We investigated the archival ground-based VLBI images of the extragalactic radio sources included in both the Wilkinson Microwave Anisotropy Probe (WMAP) and the Planck catalogues, and selected 49 bright and compact sources as potential targets for space Very Long Baseline Interferometry (VLBI) observations at mm wavelengths. These sources have a flat radio continuum spectrum between 33 and 94 GHz. They are identified as core-dominated active galactic nuclei (AGN), located at declinations above ?40°, and have never been observed with ground-based VLBI at 86 GHz. The radio properties of the 49 new sources are presented. We compare this new sample with similar samples of compact AGN available from earlier studies. The new candidates, together with the existing bright compact AGN sample identified from 86-GHz ground-based VLBI imaging surveys, form a catalogue of more than 160 AGN. These could be primary targets for mm-VLBI observations on the ground, as well as for future mm-wavelength space VLBI missions such as the project with two satellites currently under study in China. 相似文献
18.
We consider a method of reconstructing the structure delay of extended radio sources without constructing their radio images. The residuals derived after the adjustment of geodetic VLBI observations are used for this purpose. We show that the simplest model of a radio source consisting of two point components can be represented by four parameters (the angular separation of the components, the mutual orientation relative to the poleward direction, the flux-density ratio, and the spectral index difference) that are determined for each baseline of a multi-baseline VLBI network. The efficiency of this approach is demonstrated by estimating the coordinates of the radio source 0014+813 observed during the two-week CONT14 program organized by the International VLBI Service (IVS) in May 2014. Large systematic deviations have been detected in the residuals of the observations for the radio source 0014+813. The averaged characteristics of the radio structure of 0014+813 at a frequency of 8.4 GHz can be calculated from these deviations. Our modeling using four parameters has confirmed that the source consists of two components at an angular separation of ~0.5 mas in the north–south direction. Using the structure delay when adjusting the CONT14 observations leads to a correction of the average declination estimate for the radio source 0014+813 by 0.070 mas. 相似文献
19.
通过主要在短厘米波长的全球VLBI观测,已经发现强射电类星体4C39.25在十秒差距尺度结构中的视超光速运动,其运动学图景表明该源是一个很特殊的视超光速源.近几年已提出了若干模型,试图解释这特殊的运动图景.报道不多的百秒差距尺度的VLBI观测,很可能有助于检验提出的模型.本文介绍用欧洲网及上海25m天线,在18cm波长对4C39.25所作的VLBI 成象观测的初步结果,显示百秒差距尺度复杂结构及可能存在的视超光速运动. 相似文献
20.
银河系光行差,或称为长期光行差漂移,是由于太阳系质心绕着银河系中心做轨道运动的加速度引起的视自行效应,量级大约为5μas·yr~(-1).在21世纪之前,由于观测精度尚未达到如此高的程度,人们很少讨论银河系光行差效应.随着甚长基线干涉(Very Long Baseline Interferometer,VLBI)在基本天文学中的广泛应用和欧洲空间局(European Space Agency,ESA)的第2代微角秒天体测量卫星Gaia的问世,该效应显得逐渐重要.由于河外源的分布不均匀,银河系光行差效应会使得河外源天球参考架缓慢旋转,进而需要修正地球岁差参数,其中岁差速率的改正值大约为1μas·yr~(-1).对于微角秒精度的VLBI和Gaia参考架,银河系光行差将会引起框架扭曲,在两者的连接过程中,也是必须考虑的系统效应. 相似文献