The development of radio astronomy at Hartebeesthoek

The development of radio astronomy at the Hartebeesthoek Radio Astronomy Observatory in South Africa is described. The Hartebeesthoek site was established originally by NASA as one of three Deep Space Stations equipped with 26-m parabolic reflector antennas. It was first used for radio astronomy by South Africa in terms of the NASA host nation agreement which allowed for its use at times when the facility was not needed for its primary purpose of tracking space probes. After NASA withdrew from South Africa in 1975, the South African Council for Scientific and Industrial Research took over the site and the 26-m parabolic reflector antenna, which NASA had abandoned in position, and established it as a national observatory. The development of the facility to the stage where it could support a variety of observing programmes such as continuum observations and mapping, spectroscopy and pulsar timing is described as well as the role played by the Observatory in global programmes of very long baseline interferometry.     

Spectroscopic research with the Hartebeesthoek radio telescope

Research into star-forming regions, evolved HII regions, late-type stars with circumstellar dust shells and comet Halley using spectroscopic observations made with the Hartebeesthoek radio telescope is reviewed.     

On post-SKA radio astronomy

It is suggested that the development of the SKA will drastically change the face of radio astronomy in the 21st Century. A FAST-style SKA would admit observations of low contrast features, and would be the best design for studying the `dark ages' of the Universe (x≫ 1) where sub-arcmin total power instruments can usefully be employed. To date there have been no proposals for post-SKA, billion square-metra instruments; we speculate that mobile communication systems can be used. In the very distant future, SKA multi-beam systems could be used to collect signals reflected by Solar system bodies such as the asteroid belt. This revised version was published online in July 2006 with corrections to the Cover Date.     

Early Cambridge radio astronomy

Radio astronomy started in Cambridge immediately after the hostilities of the World War II have ceased. Martin Ryle was the inspiring leader of a small group that started to develop interferometry techniques at the Cavendish Laboratory. From this development came the numerous Cambridge radio source surveys culminating in the Nobel prize awarded to Martin Ryle for invention of aperture synthesis. The history of this early development is the subject of the present paper. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The development of radio astronomy

Following the detection of extraterrestrial radio waves in 1932 by Karl Jansky, radio astronomy developed quickly after World War II. It established itself soon as a new branch of astronomy with today's outstanding record in the detection of new phenomena in space. These have been honoured by a number of Nobel prizes. Radio astronomy largely depends on technical developments in receiver technology, antenna systems, electronics and computing power. Ever shorter wavelengths down to the submm‐wavelength range became accessible, resulting in new exciting discoveries. However, now and in future care must be taken, in particular for the lower frequency range, of harmful man‐made interferences, which might mask the weak signals from space. New international facilities with orders‐of‐magnitude higher sensitivity like ALMA and SKA are planned or under construction. Space‐borne observatories like PLANCK will detect weak fluctuations of the cosmic microwave background, which will constrain cosmological models with an unprecedented accuracy.     

Analysis of radio astronomy bands using CALLISTO spectrometer at Malaysia-UKM station

The e-CALLISTO system is a worldwide network that aims to observe solar radio emission for astronomical science. CALLISTO instruments have been deployed worldwide in various locations that together can provide continuous observation of the solar radio spectrum for 24 h per day year-round. Malaysia-UKM is a strategic equatorial location and can observe the Sun 12 h per day. This paper gives an overview of the spectrum allocation for radio astronomy, which falls in the specified operating frequency band of the CALLISTO spectrometer. The radio astronomy bands are analyzed at the Malaysia-UKM station according to the International Telecommunication Union recommendations. Some observational results are also presented in this paper.     

The faint radio sky: radio astronomy becomes mainstream

Radio astronomy has changed. For years it studied relatively rare sources, which emit mostly non-thermal radiation across the entire electromagnetic spectrum, i.e. radio quasars and radio galaxies. Now, it is reaching such faint flux densities that it detects mainly star-forming galaxies and the more common radio-quiet active galactic nuclei. These sources make up the bulk of the extragalactic sky, which has been studied for decades in the infrared, optical, and X-ray bands. I follow the transformation of radio astronomy by reviewing the main components of the radio sky at the bright and faint ends, the issue of their proper classification, their number counts, luminosity functions, and evolution. The overall “big picture” astrophysical implications of these results, and their relevance for a number of hot topics in extragalactic astronomy, are also discussed. The future prospects of the faint radio sky are very bright, as we will soon be flooded with survey data. This review should be useful to all extragalactic astronomers, irrespective of their favourite electromagnetic band(s), and even stellar astronomers might find it somewhat gratifying.     

Frequency selective surfaces for radio astronomy

Frequency selective surfaces (FSSs) with the Jerusalem-cross array configuration have been developed for simultaneous observations of radio astronomical sources at the 40GHz and 80GHz bands. For supporting material, PET(polyethylene terephthalate: 200×220mm large, 12m thick, permittivity 3.0) was used, and copper was used for the conducting array. The measured characteristics were in good agreement with the calculated ones. The fabricated FSS has low insertion losses of less than 0.2dB and little distortion of polarization for each band. The characteristics of the developed FSS satisfy radio astronomical requirements.     

GPU accelerated radio astronomy signal convolution

The increasing array size of radio astronomy interferometers is causing the associated computation to scale quadratically with the number of array signals. Consequently, efficient usage of alternate processing architectures should be explored in order to meet this computational challenge. Affordable parallel processors have been made available to the general scientific community in the form of the commodity graphics card. This work investigates the use of the Graphics Processing Unit in the parallelisation of the combined conjugate multiply and accumulation stage of a correlator for a radio astronomy array. Using NVIDIA’s Compute Unified Device Architecture, our testing shows processing speeds from one to two orders of magnitude faster than a Central Processing Unit approach.     

Estimating the size of a radio quiet zone for the radio astronomy service

The size of a radio quiet zone (RQZ) is largely determined by transmission losses of interfering signals, which can be divided into free space loss and diffraction loss. The free space loss is dominant. The diffraction loss presented in this paper is described as unified smooth spherical and knife edge diffractions, which is a function of minimum path clearance. We present a complete method to calculate the minimum path clearance. The cumulative distribution of the lapse rate of refractivity (g _n ), between the earth surface and 1 km above, is studied by using Chinese radio climate data. Because the size of an RQZ is proportional to g _n , the cumulative distribution of g _n can be used as an approximation for the size of the RQZ. When interference originates from mobile communication or television transmissions at a frequency of 408 MHz, and $\overline {g_n } $ is 40 N/km, where the refractivity $N=\left( {n-1} \right) \times 10^6$ , the size of the RQZ would be 180 km for a mobile source or 210 km for a television source, with a probability in the range of 15–100% in different months and for different stations. When speaking of the size of an RQZ, the radius in the case of a circular zone is implied. It results that a size of an RQZ is mainly influenced by transmission loss rather than effective radiated power. In the case where the distance between an interfering source and a radio astronomical observatory is about 100 km, at a frequency of 408 MHz, the allowable effective radiated power of the interfering source should be less than ?30 dBW with a probability of about 85% for $\overline {g_n } $ equals 40 N/km, or ?42 dBW with a probability less than 1 % for $\overline {g_n } $ equals 80 N/km.     

Observation of solar radio emission by the 22-m radio telescope at the Crimean Astrophysical Observatory at 2.25 mm and 8.15 mm wavelengths

The results are given of observation of solar radio emission of the S-component at 8.15 mm-, and 2.25 mm- made with the 22 m radio telescope of the Crimean Astrophysical Observatory. Solar radio images are obtained at both wavelengths. The data are presented of radio emission intensity and brightness temperatures of 10 sources of the S-component as well as the result of a flare observed. The sources of the S-component appear to be opaque at millimetre wavelengths.     

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.     

Results of the first two years of VLBI observations at the Svetloe Observatory within the framework of international geodynamical programs

We present the results of processing the VLBI observations performed at the Svetloe Observatory of the Institute of Applied Astronomy (IAA), Russian Academy of Sciences, in the period 2003–2005 within the framework of geodynamical programs of the International VLBI Service (IVS) for geodesy and astrometry. We analyzed the observations at the Svetloe Observatory, together with the observations at other stations of the global IVS network, at the IAA using a modified OCCAM package. The package uses new reduction models that decrease the systematic errors of the results. The motion of the stations, primarily of the Svetloe Observatory, is investigated to study the global geotectonic processes. Highly accurate estimates of the coordinate and baseline length variations have been obtained for the first time in Russia from observations at a Russian VLBI station. We determined the coordinates and velocity of the Svetloe VLBI station with errors of ～2 mm and 3 mm yr^?1, respectively, and the baseline lengths between the stations with a sufficiently long observational history with an accuracy of 1–3 mm. The results are shown to be in good agreement with currently available models for the motion of tectonic plates.     

Suggestions for some single dish radio astronomy standards

In this paper we examine the possibility of adopting standards within the context of radio astronomy and the benefits to be derived thereby. In particular we consider the application of standards within the three areas of the receiver hardware, the control and communication between different parts of the observing system, and the interface with the astronomer. The adoption of such standards will increase flexibility of observing systems, allow the easy interchange of equipment between observatories and greatly simplify guest observing. In this paper we will only consider the application of standards within the field of millimetre-wave and sub-millimetre-wave single dish astronomy. However, the principle can be easily extended to other astronomical wavebands. We describe some current developments at the Onsala Space Observatory which illustrate the proposed philosophy and show how such standards may be implemented. Naturally, the detailed definition of such standards would have to be agreed in conjunction with other interested astronomical institutions.