VLBI at the Hartebeesthoek radio astronomy Observatory

The Hartebeesthoek Radio Astronomy Observatory has played a key role in the development of very long baseline interferometry (VLBI) in the southern hemisphere since 1971. This paper describes how the VLBI programme evolved and the instrumentation used. Contributions to high resolution mapping of compact radio sources are described, for both the Southern Hemisphere VLBI Experiment, SHEVE, and for Global networks, where HartRAO has made significant improvements in the N-S resolution. The unique geographical location of the telescope has been used to establish the terrestrial reference frame in the southern hemisphere and to measure tectonic motions over the past nine years. The Observatory has also been a fundamental station in extending the celestial reference frame defined by extragalactic radio sources to the southern hemisphere, and results of these programmes are given.     

三颗河外射电源第一历元的VLBI图像

本文给出利用上海、乌鲁木齐、意大利ＮＯＴＯ和南非ＨａｒｔＲＡＯ射电望远镜,对三颗河外射电源（１５３２＋０１６,２３２００２０,２３５１１５４）,在５ＧＨｚ频率上的第一历元ＶＬＢＩ观测成图结果     

The Rhodes/HartRAO 2326-MHz radio continuum survey

We have made scanning observations with the HartRAO 26-m radio telescope to obtain a pencil-beam map of 67 per cent of the sky at 2326 MHz. This is the highest resolution and highest frequency radio continuum map of this type made of such a large area of sky.   In this paper we describe the observations and data reduction procedures used to produce the survey. The resulting map has an angular resolution (HPBW) of 20 arcmin, and the rms pointing accuracy is 1.2 arcmin. The rms noise fluctuations are less than 30-mK T _FB over the whole map. We estimate that the uncertainty in the temperature scale is less than 5 per cent, and that the error in the absolute zero level is better than 80-mK T _FB in any direction.   High-contrast half-tone images of the data with a model of the diffuse galactic background subtracted are presented. These images show many complex emission structures up to and beyond 50° latitude, and illustrate the quality of the data. Extracts from the survey data are available via FTP by arrangement with the authors.     

Radio astronomy and very large telescopes

The current achievements of the observational abilities of radio astronomy is briefly reviewed putting emphasis on the imaging capability. The new projects in radio astronomy are discussed in connection with the new generation of optical/IR telescope projects.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 1988.     

Hydrodynamic Instability of Ionization Front in HII Regions: From Linear to Nonlinear Evolution

A sample of 54 6.7-GHz methanol maser sources was monitored at HartRAO for 4 years, and 11 12.2-GHz methanol masers for 3 years. The majority of the maser features display a significant degree of variability but with a wide range of timescales and behaviors. Some maser features remained unvarying throughout the monitoring programme, while others showed sporadic flares or sudden drops in flux density. Yet another group show quasi-periodic and periodic variations. In some cases the maser features dropped below the detection limit for a significant length of time before increasing in intensity and reappearing.     

Site evaluation and RFI spectrum measurements in Portugal at the frequency range 0.408–10 GHz for a GEM polarized galactic radio emission experiment

We probed for radio frequency interference (RFI) at three potential galactic emission mapping experiment (GEM) sites in Portugal using custom made omnidirectional disconic antennas and directional pyramidal horn antennas. For the installation of a 10-m dish dedicated to the mapping of polarized galactic emission foreground planned for 2005–2007 in the 5–10 GHz band, the three sites chosen as suitable to host the antenna were surveyed for local radio pollution in the frequency range 0.01–10 GHz. Tests were done to look for radio broadcasting and mobile phone emission lines in the radio spectrum. The results show one of the sites to be almost entirely RFI clean and showing good conditions to host the experiment.     

10颗近赤道弱源MK2VLBI观测结果

本文给出利用中国、意大利、南非射电望远镜对一个近赤道源样本在５ＧＨｚ频率上进行ＭＫ２ＶＬＢＩ普测中１０颗弱源的相关流量和其中部分源用ＨａｒｔＲＡＯ望远镜观测的总流量值，作为进一步的ＭＫ３或ＶＬＢＡ记录系统的ＶＬＢＩ观测依据．     

Surveys of compact extragalactic radio sources

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.     

Phaseless VLBI mapping of compact extragalactic radio sources

The problem of phaseless aperture synthesis is of current interest in phase-unstable VLBI with a small number of elements when either the use of closure phases is not possible (a two-element interferometer) or their quality and number are not enough for acceptable image reconstruction by standard adaptive calibration methods. Therefore, we discuss the problem of unique image reconstruction only from the spectrum magnitude of a source. We suggest an efficient method for phaseless VLBI mapping of compact extragalactic radio sources. This method is based on the reconstruction of the spectrum magnitude for a source on the entire UV plane from the measured visibility magnitude on a limited set of points and the reconstruction of the sought-for image of the source by Fienup's method from the spectrum magnitude reconstructed at the first stage. We present the results of our mapping of the extragalactic radio source 2200+420 using astrometric and geodetic observations on a global VLBI array. Particular attention is given to studying the capabilities of a two-element interferometer in connection with the putting into operation of a Russian-made radio interferometer based on Quasar RT-32 radio telescopes.     

Software Development For The Square Kilometre Array

Software development costs for the Square Kilometre Array are likely to be very large – in the range of 1000–2000 person-year a total. This level of software effort is unprecedented in radio astronomy. Consequently the risk associated with software development is very large. This is common to many large science projects and so we can learn from such projects how to best mitigate against the risk. We present a shopping list of suggestions drawn from the experience in other projects.     

恒星射电耀发6cm波段偏振观测试验

利用新疆天文台南山基地25m射电望远镜在6cm波段对恒星V772 Her和βPer进行了偏振观测试验.通过数据处理和校准得到恒星的射电光变曲线.探测到V772 Her的射电耀发现象,耀发时的线偏振度约达30%,偏振位置角约4°;探测到βPer的缓变成份及叠加其上的快速耀发,βPer耀发时线偏振很弱.     

Mapping the sun with the RTF-32 radio telescopes

The possibilities of using the RTF-32 radio telescopes of the interferometric QUASAR network for solar observations are investigated. A technique of solar radio mapping with the RTF-32 telescopes is presented. The software developed at the Institute of Applied Astronomy, Russian Academy of Sciences, for reducing such observations is described. The maps of the Sun at 1.35 cm, derived from observations at the Zelenchukskaya observatory November 4–14, 2004, are presented.     

未来的国际天球参考架

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     

Radio astronomy at the University of Sydney

The recent improvements to the radio telescopes at the Molonglo (MOST) and Fleurs (FST) Observatories are described along with some of the astronomical projects.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Multi-Wavelength Studies on H2O Maser Host Galaxies

H₂O maser emissions have been found in external galaxies for more than 30 years. Main sciences associated with extragalactic H₂O masers can be summarized roughly into three parts: maser emission itself, AGN sciences and cosmology exploration. Our work in this field focusses on two projects: X-ray data analysis of individual maser source using X-ray penetrability to explore maser host obscured AGN; multi-wavelength statistical properties of the whole published H₂O maser sample. Here their nuclear radio properties were investigated in detail, based on their 6-cm and 20-cm radio observation data. Comparing the radio properties between maser-detected sources and non-detected sources at similar distance scale, we find that: (1) maser host galaxies tend to have higher nuclear radio luminosity; (2) the spectral index of both samples is comparable (～0.6), within the error ranges. In addition, for AGN-maser sources, the isotropic maser luminosity tends to increase with rising radio luminosity. Thus we propose the nuclear radio luminosity as one good indicator for searching AGN-masers in the future.     

Magnetic fields in galaxies

Summary Recent years have seen an amazing development in our knowledge of the magnetic fields in the universe. The last ten years were crucial in our realization of the importance of the magnetic fields in galaxies. While a lot of the earlier data on our Galaxy depended on optical observations, the bulk of the recent results depend on radio measurements. The radio Zeeman effect gave us new information on magnetic fields in molecular clouds. The mapping of galaxies at several radio frequencies resulted in new knowledge about the large-scale magnetic fields in these basic building blocks of the universe. These exciting observations have led to new theoretical developments. In particular, the dynamo theory of flat objects received much attention since the observed large-scale structures can best be explained through the action of the dynamo effect. This review will attempt to summarise the observational evidence and to give viable explanations for the magnetic fields in galaxies.     

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     

Solar brightness distribution and its variability at 3 millimeter wavelength

Solar mapping at 3.4 millimeter wavelength has shown the existence of various spatial structures in brightness distribution. The most prominent structure is presented by the local sources of the slowly varying component of the solar radio emission. Usually they coincide with active regions. Some sources have no corresponding optical counterparts. Using synoptic radio maps, latitudinal belts of enhanced brightness were detected at the north and south hemispheres. These belts seem to coincide with sunspot zones, but the enhanced emission exists independently of sunspot group appearance. Comparison of our maps with XUV images shows a noticeable resemblance. Sources above active regions and latitudinal belts of enhanced brightness are seen in both ranges as well as coronal holes.     

CO Clouds around SNR G21.8-0.6 and G32.8-0.1

We made the first CO(I—0) mapping to SNR G21.8-0.6 and SNR G32.8-0.1, both associated with OH 1720 MHz maser.Based on the morphological correspondence and velocity and position agreement between the radio remnant and the CO clouds,we tentatively identify the clouds that are respectively interacting with the two SNRs.     

Measuring supermassive black holes via reverberation mapping in the UV

Over the past three decades the reverberation mapping technique was used to measure the central regions of Active Galactic Nuclei (AGN), their size, velocity field, and the mass of the black hole in the center. This technique was used mainly in the optical with several studies in the UV. Reverberation mapping in the UV adds essential information to the AGN studies. This paper reviews these recent studies done in the UV, presents results from the recent HST campaign toward NGC?5548, and discuss two projects of reverberation mapping of UV emission lines in high-luminosity quasars. The advantages of reverberation mapping in the UV will be discussed as well as the needs from new UV missions in order to be able to advance UV reverberation mapping campaigns.