M. I. Large

Increasing the Field Size of the Molonglo Observatory Synthesis Telescope

The Molonglo Observatory Synthesis Telescope (MOST), which at present images a fully synthesised 70′ field in 12 h, is being converted to enable observing modes which extend the field size to 160′. The new observing modes will allow the MOST to survey completely the sky south of δ = −30° to a (5σ) sensitivity limit of about 5 mJy. The result will be a catalogue of over 400,000 radio sources with a spatial density of less than 1 source per 100 beam areas, providing the foundation for a number of novel astronomical and cosmological investigations. The conversion involves construction of 352 low-noise HEMT preamplifiers, 88 digitally controlled UHF quad phase shifters, 88 mixers and IF sections, a new communication and control system, and several other new sub-systems. The project has been funded and developments are well advanced.

Continuum Radio Spectrum of the Flare Star AT Mic.

The binary flare star AT Mic has been observed with the VLA (5 GHz and 1.5 GHz) and, nearly simultaneously, with the MOST (0.843 GHz). There appears to be a slowly varying component of the radio intensity, with a flux density greater at 0.843 GHz than at higher frequencies. It is suggested that above 1 GHz the emission is possibly produced by incoherent gryosynchrotron radiation, whereas below 1 GHz a coherent mechanism predominates.

Response of the Molonglo Observatory Synthesis Telescope to Terrestrial Interference

In conjunction with the Australian Governments Spectrum Management Agency, experimental tests have been carried out to determine the susceptibility of the Molonglo Observatory Synthesis Telescope (MOST) to interference from terrestrial transmitters. The motivation for the tests was to reconcile the conflicting requirements of the MOST, which is committed to an extensive survey of the southern sky at 843 MHz, with the commercial use of the 825-845 MHz band, which is being prepared for sale. The tests show that the far sidelobe gain of the MOST, relative to an isotropic antenna is generally less than 1, and that an appropriate interference criterion would be that in-band interference irradiance should not exceed -173 dB W m^-2. This value is similar to that considered by the International Telecommunications Union to be detrimental to radio astronomy continuum observations at nearby frequencies.

The Australian Radio Star Survey

We present an overview of the survey for radio emission from active stars that has been in progress for the last six years using the observatories at Fleurs, Molonglo, Parkes and Tidbinbilla. The role of complementary optical observations at the Anglo-Australian Observatory, Mount Burnett, Mount Stromlo and Siding Spring Observatories and Mount Tamborine are also outlined. We describe the different types of star that have been included in our survey and discuss some of the problems in making the radio observations. Introduction During the last six years the radio observatories of Australia have been collaborating in a major survey of active radio stars. Table 1 lists these observatories, together with some of their observing parameters. At the same time, several Australian optical observatories—both large and small—have been involved in complementary optical observations (see Table 2). Other papers to be presented at this meeting will describe some of the initial results of this survey (Slee et al. 1987b, Vaughan et al. 1987 and Beasley et al. 1987). In this paper, however, we Division of Radiophysics, CSIRO, Sydney Department of Mathematics, Physics, Computing and Electronics, Macquarie University, Sydney School of Physics, University of Sydney School of Electrical Engineering, University of Sydney Department of Physics, Monash University, Melbourne Mount Stromlo and Siding Spring Observatories, ACT Anglo-Australian Observatory, Sydney Mount Tamborine Observatory, Queensland shall attempt to set to set the background and give an overview of our collaborative program. Radio Stars The overwhelming majority of even the brightest stars in the sky cannot be detected with existing radio telescopes. This is because radio telescopes detect best those sources that are either big or hot, or, more accurately, sources that have a large angular size or a high brightness temperature. The radio flux density, S (mJy) measured for a star of angular diameter 6 (arcsec), brightness temperature T (K) and at an observing frequency v (GHz) is given by

The Reduction of Radio Source Positions to Standard Epoch

The usual method of calculating corrections for precession nutation and aberration involves the use of the precession constants M, N, m, n and the Day Numbers A, B, C, D, E, J, J’ . For the computer analysis of radio source data obtained with the Molonglo Telescope it seemed desirable to compute the corrections directly from the basic formulae, thus avoiding the trouble and possibility of accidental error in copying out the Day Numbers for each day’s observation. In this paper we quote in full the equations that are used in the analysis of the Molonglo data. These equations are abstracted from The Explanatory Supplement to the Astronomical Ephemeris and Smart’s Spherical Astronomy , and expressed in a form which parallels the organization of the computer routine. In addition to the observed position, the only other data required to compute the precession nutation and aberration corrections is the Julian date (J.D.). This basic parameter in the equations is very simply calculated to the required accuracy of a few minutes from the time and date of the observation. The computer routine that computes the corrections occupies 1350 words of programme in the KDF9 computer and takes 200 msec to compute one position. If a large number of computations are being carried out on continuous data, then the average time per computation is only 5 msec as a full computation of the coefficients does not have to be made for each point separately.