Alan E. Wright

Redshifts of southern radio sources. VII

Redshifts and low-resolution spectral data are presented for 47 objects, most of which are QSOs identified with flat-spectrum radio sources from the Parkes 2.7 GHz survey. These data were taken with the 3.9 m Anglo-Australian Telescope using both the IPCS and FORS spectrographs. The total spectral coverage is 3200-9500 A. Three objects are optical counterparts identified with IRAS sources. 55 references.

PKSCAT90: the Southern Radio Source Database

The PKSCAT90 database consists of radio and optical data for 8264 radio sources. It covers all the sky south of declination +27 degrees. Most of the galactic plane and the Magellanic Cloud regions are excluded from this catalogue but have been the subject of other specialised surveys. A few data errors in the initial PKSCAT90 version 1.00 released in March 1990 have been corrected in the current version 1.01 edition.

The optical identification content of the Einstein Observatory deep X-ray survey of a region in Pavo

Results are presented from the Einstein deep X-ray survey in Pavo, with correlated optical and radio observations of a complete sample of candidate identifications. There are 16 X-ray sources detected with positional accuracy better than 10 arcsec, of which five are identified, with a further seven (and a maximum nine) probable identifications. Of the identified sources, four are QSOs with J-magnitude about 20 (one is an inverted spectrum radio source) and one is associated with extended emission from a pair or cluster of galaxies. Of the probable identifications, one is a galaxy and the rest are a subset of a yellow stellar object population which may also be QSOs. Identifications with QSOs and QSO candidates with J less than 24 account for 60-80 percent of the detected sources.

Flux Densities at 8400 MHz for a Large Sample of Parkes Radio Sources

We give a progress report on a programme of observations to obtain flux densities at 8.4 GHz for a large sample of radio sources selected from the Parkes 2700 MHz Survey. So far, about 1000 flux measurements have been made with a typical accuracy of 10%.

VLBI observations of a radio flare of Circinus X-1

VLBI 2.3 GHz observations of a strong radio flare of the binary star system Circinus X-1 indicate a radio source flaring component angular size of 0.0015-0.015 arcsec. This is equivalent to a linear size of 15-150 AU at the 10 kpc distance of Circinus X-1, although interstellar medium scattering may have enlarged the apparent angular source size. Since the radio source quiescent component, observed prior to the flare, had an angular size greater than 0.2 arcsec (equivalent to more than 2000 AU at 10 kpc), the quiescent radio emission comes from a region much larger than that proposed in recent models for Circinus X-1. The quiescent component appears to be variable on a time scale of years, and is probably fueled by the Circinus X-1 binary system.

Multifrequency radio observations of optically selected quasars

A complete sample of 12 radio sources stronger than 10 mJy at 5.0 GHz are identified with optically selected quasars (discovered with the Curtis-Schmidt telescope) on the basis of precise radio-optical position coincidence. Radio spectra determined from flux densities at 0.408, 1.465, 2.29, 5.0, and 14.5 GHz indicate synchrotron self-absorption in 11 cases. The only steep-spectrum source is resolved by the VLA at 1.465 GHz. It is shown that the spectral-index distributions of radio sources identified with optically selected quasars can vary only weakly with radio finding frequency since the radio number-flux-density relation of these identifications is so flat. The number-magnitude distributions of radio-selected and optically selected quasars are compared and interpreted in terms of a radio-optical core-flux correlation. Finally, physical differences between radio-selected and optically selected quasars are considered. We find that differing orientations of relativistically beamed radio jets cannot explain the differences between the radio luminosity functions of radio-selected and optically selected quasars.

The Parkes-MIT-NRAO Southern Sky Survey at 4850 MHz

G. Behrens, C. Chestnut, National Radio Astronomy Observatory, Greenbank, USA B. F. Burke, A. Fletcher, Massachusetts Institute of Technology, Cambridge, USA K. S. Russell, A. Savage, UK Schmidt Telescope, Anglo-Australian Observatory, Coonabarabran NSW 2357 J . L im, A. E. Vaughan, School of Mathematics and Physics, Macquarie University, North Ryde NSW 2113 S. Cote, Mount Stromlo and Siding Spring Observatories, Private Bag Weston ACT 2611 M. Anderson, A. Hons, G. L. White, Faculty of Science and Technology, University of Western Sydney, Kingswood NSW 2747 S. Amy, A. Burgess, S. Chan, L. Cram, A. Gray, W . Walsh, D. Campbell-Wilson, Astrophysics Department, University of Sydney, NSW 2006 V. Mclntyre, P. Randall, M. Suters, W. J. Zealey, Department of Physics, University of Wollongong, Wollongong NSW 2500

Universal Gravity: was Newton Right?

We question Newton’s inverse square law of universal gravitation in the light of recent, alternative formulations. In addition, we present numerical simulations of galaxy interactions which were used in an attempt to distinguish between an inverse square law and an inverse linear law. We conclude that an inverse linear relation is as compatible with the observational data on interacting galaxy systems as the inverse square law.

VLBI observations of the nucleus of Centaurus A

VLBI observations of the nucleus of Centaurus A have been made at three southern hemisphere observatories. Since Centaurus A is the nearest active galaxy, VLBI investigations are important because the physical processes in the nucleus can be studied in greater linear detail than in other similar galaxies. Previous VLBI observations of Centaurus A have been hampered by its southerly declination (-43°) and the sparsity of VLBI capability in the southern hemisphere, leading to only scattered single point u,v coverage. This paper presents results from the early stages of development of a southern hemisphere VLBI network.

A Search for 43.122 GHz SiO Emission from Symbiotic Stars

During the second half of 1986 tests were made of a new Q-band (43 GHz) receiver designed for the Parkes radio telescope. As part of the trial observation program 12 symbiotic stars were examined for SiO maser emission. No significant new emission was detected from any of the candidates, although several previously known SiO sources (including one symbiotic star) were confirmed. We conclude that potential SiO maser action near the Mira star in most symbiotic systems is prevented by the presence of the hot companion star.