Michael J. Batty

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.

Parkes-Tidbinbilla interferometer

The design and construction of the Parkes-Tidbinbilla interferometer (PTI), a radio-linked interferometer using the 64-m Parkes telescope together with either the 34-m or 64-m NASA telescopes at Tidbinbilla, are described. The interferometer has a baseline of 275 km and a sensitivity of 1-3 mJy rms at a bandwidth of up to 10 MHz. The instrument provides angular resolutions of 0.13 arcsec at 1.7 GHz, 0.09 arcsec at 2.3 GHz, and 0.03 arcsec at 8.4 GHz. PTI projects discussed include the study of SN 1987A, astrometric measurements of calibrator sources, and the determination of pulsar proper motions. 10 references.

2.3-GHz accurate positions and optical identifications for selected Parkes radio sources

Accurate radio positions of 74 extragalactic radio sources contained in the Parkes 2.7-GHz survey were measured at 2.3 GHz with the Tidbinbilla interferometer, located near Canberra, Australia. The radio sources, most of which lie between declinations -30/sup 0/ and -35/sup 0/, were measured to an rms positional accuracy of approx.3 arcsec relative to a grid of previously identified radio sources. Optical identifications have been made on the basis of positional coincidence alone, without regard to color or morphology, using the UK Schmidt telescope deep IIIa-J sky survey plates. Identifications are suggested and accurate optical positions have been measured for 62 objects brighter than magnitude 22.5 on the IIIa-J plates.

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.

Accurate radio and optical positions for the radio star HD 36705 (AB Doradus)

Arc-second position measurements of the active star HD 36705 (AB Dor) and of the variable radio source found nearby are presented. These measurements show that the radio source is clearly identified with HD 36705 and not with the nearby red-dwarf star Rst 137B.

Tidbinbilla Two-Element Interferometer

A phase-stable two-element interferometer has been formed by linking the 64- and 34-m antennas of the Deep Space Network at Tidbinbilla, Australia. Utilizing the existing first-stage maser receivers at 2.3 GHz to yield a system temperature of approximately 20 K, the system has a 5 sigma detection sensitivity of 50 mJy in 1 s, with a rms confusion of approximately 6 mJy. The 195-m north-south baseline permits positional measurements to approximately 2 arcsec of sources stronger than approximately 100 mJy over the declination range -80 to +30 deg. Such measurements are ideally suited for the optical identification of weak radio sources. It is planned to extend the frequency of operation of the instrument to 8.4 GHz in the near future.

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.

1934-638 revisited

A red CCD image of the galaxy identified with the compact southern radio source 1934-638 shows it to consist of two compact components enclosed within a low-surface-brightness nebulosity. Comparison of accurate radio and optical positions shows that the radio source is coincident with the brighter of the two components and that 1934-638 is unlikely to be a dust-lane galaxy like Centaurus A.

Sensitive ammonia observations in the southern hemisphere

The 64-m spacecraft communication antenna of the NASA-JPL Deep Space Network has been equipped for spectral line observations at K band (18--25 GHz). To demonstrate the potential of this system, preliminary observations of the (1, 1) transition of ammonia are reported for a selection of eight southern molecular clouds. Estimates of gas density and ammonia column density are reported for six sources.

The Tidbinbilla interferometer

A proposal to operate a two element interferometer using the 64 m and 26 m antennas of the Tidbinbilla Deep Space Station is discussed. The instrument is to be operated as a correlation interferometer, the sine and cosine products being sampled once per second and recorded for later analysis. The receiver systems are currently under development. Preliminary measurements of the delay line and local oscillator systems and the site cables suggest that a phase stability to within about 1 deg should be achievable with temperature control of the receiver packages.