O. B. Slee

Scattering of pulsar radiation and electron density turbulence in the interstellar medium

We report measurements, using the Culgoora circular array at 80 and 160 MHz and the Parkes 64 m telescope at 410 MHz, of the pulse broadening due to interstellar scattering on 33 pulsars. These results are added to published data on 52 other pulsars in order to investigate the interstellar turbulence levels over 85 paths in the Galaxy. We find a significant relation between the turbulence level C~ and dispersion measure, heliocentric distance, galactocentric distance, galactic latitude and galactic longitude. Our results are consistent with a distribution of turbulence that peaks near the galactic centre and extends out to past the solar circle, with the scale height perpendicular to the plane at least equal to that of the pulsars. The magnitude of the fluctuations in electron density responsible for the scattering is not proportional to the average electron density, but increases much more rapidly than the latter as the galactic centre is approached. The apparent dependence of C~ on heliocentric distance is preferentially interpreted as due to the presence of a highly clumped distribution of turbulence along all lines of sight.

Radio emission from EA eclipsing binaries - Evidence for kilogauss surface fields on both early-type and late-type stars

Radio observations of a sample of EA eclipsing binaries, including early-type main-sequence pairs as well as classical Algol-type eclipsing binaries, indicate the presence of a moderately strong coronal magnetic field, B of about 100 G, between the component stars. This translates to a surface magnetic field of about 1000-10,000 G on one or both stars. This is the first compelling evidence for magnetic fields on early-type stars, apart from the Ap and Bp magnetic stars first detected in 1947. 47 refs.

Flux densities, spectra and variability of pulsars at metre wavelengths

We present the results of two-frequency flux density measurements of 74 pulsars with the Culgoora circular array. We show that the spectral index of a typical pulsar steepens markedly from 80 to 1400 MHz, but we found no significant relationship between the metre-wave spectral index and the published pulsar parameters

Power spectral analysis of enhanced scintillation of Quasar 3C459 due to Comet Halley

The radio source 2314+038 (3C459) showed enhanced scintillations on three days at a solar elongation of about 90° as the plasma tail of Halleys Comet swept across it on six days during 16-21 December 1985. If we assume that the plasma velocities in the tail were not constant everywhere, but increased linearly from about 50 kms-1 at the tail axis to the normal average solar wind velocity of 400 kms-1 at the edges where the tail merged with the solar wind, a power spectral analysis of the scintillations shows two ranges of the rms electron density variation t:..N and scale size a. In particular, these are a fine scale zone near the axis where a is in the range 9 to 27 km and t:..N in the range 2 to 5 cm -3 and a zone near the edges with a and t:..N in the ranges 100 to 265 km and 0·4 to 0·8 cm-3 respectively. The assumption of a single velocity of 100 kms-1 throughout the tail shows similar fine scales near the tail axis and large scales near the edges. The scale sizes in that case range from about 18 km at the axis to about 70 km at the edges, corresponding to t:..N of 3·3 and 0·85 cm-3 respectively. A comparison with the results obtained by Slee et al. (1987) shows that there is no radial variation of t:..N. The tail-lag is seen to playa crucial role in determining the correct occulting geometry and the path of the source through the tail.

Enhanced radio source scintillation due to Comet Austin (1989c1)

Enhanced scintillations in the direction of the quasar 2204+29 (3C441) were observed on 13 May 1990 when the tail of Comet Austin passed in front of it. Comparison with previous observations at 103, 327 and 408 MHz of Comet Halley and at 408 MHz of Comet Wilson show that proper occultation geometry is essential for observing enhanced scintillations. It has been shown that the solar elongation ? during such observations should be large, typically greater than 60· and in no case less than 30· at 103 MHz. At the time of the occultation the scintillation index (r.m.s./mean source flux) was greater than that expected for this source by a factor of 3. The r.m.s. electron density variation /IN, at a distance of 0·9 A.U. from the sun and 7·3· downstream of the nucleus, was found to be 6 cm-3 as compared with 1 cm-3 for the normal solar wind at 1 A.U. The corresponding scale sizes of the turbulence were found to be much finer than normally found in interplanetary scintillation (IPS) caused by the solar wind.

Microwave emission from southern contact-binary stars

We report the results of high-sensitivity 4.8 GHz observations of four southern contact-binary stars (AE Phe, YY Eri, RW Dor, and V757 Cen) made with the Australia Telescope Compact Array. None of these stars were detected above a 4σ level of 0.4 mJy. A comparison of the radio emission properties of contact binaries (derived from this study and from the literature) to those of short-period RS CVn stars, suggests that a decrease in the dynamo efficiency of binary stars as they approach contact may be required to explain the lower intrinsic radio luminosity of contact binaries

Radio Emission from EA Eclipsing Binaries: Evidence for Kilogauss Early- and Late-Type Stars

A recent survey of EA eclipsing binaries by the Parkes 64-m telescope operating at 8.4 GHz detected 15 out of 47 systems on at least one out of the 10 nights surveyed. The detected systems were HD 6882 (ξ Phe), HD 36486 (δ Ori A), HD 39780 (TZ Men), HD 57167 (R CMa), HD 58713 (RY Gem), HD 74307 (S Cnc), HD 132742 (δ Lib), HD 147683 (V769 Sco), HD 161741 (V393 Sco), HD 163708 (V1647 Sgr), HD 16871Q (XZ Sgr), HD 183794 (V822 Aql), HD 187949 (V505 Sgr), HD 199005 (KZ Pav), and HD 207098 (δ Cap).