Following the detection of the 9 cm ground-state triplet of CH by Rydbeck et al. (1973), preliminary observations at the CH frequencies were made with the Parkes 64-m telescope (beamwidth ∼6′ arc) in December 1973 and January 1974. We have detected the CH lines in many galactic HII regions and in the direction of the galactic centre.

The existence of red supergiants such as those in the clusters h and χ Persei has puzzled stellar evolution theoreticians for some time. Suggested explanations for them have included stars in a stage of gravitational contraction to the main sequence, or between nuclear burnings, core helium burning stars, and stars burning carbon or oxygen in the core, but it is now generally accepted that most red supergiants are core helium burning stars.

The Physics Department at the University of Otago, Dunedin, New Zealand, has over the past three years commenced a research and teaching programme in astronomy and astrophysics. Observing facilities now include two metric wave meridian transit telescopes at a site 6 km from Dunedin and a 16-inch optical telescope, formerly at Mt John, which is now sited 4 km from Dunedin at the Signal Hill observatory built by the University’s Surveying Department for geodetic work.

A combined multi-station radar equipment of c.w. and pulse at 27 MHz was used at Adelaide (lat. 35°S) during the period December 1968 to June 1969 and again in October 1969 to measure radiants and velocities of individual meteors down to limiting radio magnitude MR = + 8. Reflections from 3 to 5 points typically separated by 2 to 6 km along each trail were used and corrections for the effects of meteor region winds and wind shears were included. To date 1667 orbits have been determined from 6 months of data.

Frequency dependent structure is not uncommon in observations of extended radio sources. Where a source consists of two components with different spectra at an angular separation considerably less than the resolution of the telescope, the centroid position will vary systematically with frequency. A well-known example is 3C 273 though the effect in this case is quite small. With beams of a few minutes of arc, larger position differences could occur between measurements made at widely separated frequencies without the source being noticeably resolved. In a preliminary study of a sample of 120 4C radio sources, Munro and Hoskins found 17 cases of discrepancies in the range 45 to 100 seconds of arc between positions measured at 408 MHz with the Molonglo cross (beam width ~3′ arc) and at 2700 MHz with the Parkes 64 m telescope (beam width ~7′ arc) by Wills and Bolton. These separations were considered to be significant in terms of the quoted errors which were typically 10 to 15″ arc in each coordinate for both sets of measurements. It was pointed out that to explain the results on the basis of a double source model it would be necessary for the two components to differ in spectral index by ~1.

Observations of the red giants in NGC 1866 in the Large Magellanic Cloud, made by Arp and Thackeray provide a strict test for core helium burning models of about 5M⊙. The main observational features to be reproduced theoretically are the luminosity of the red giants, the range in effective temperature that they occupy and the ratio of the number of giants near the blue end of this range to the number at the bottom of the red giant branch. Meyer-Hofmeister attempted a theoretical fit to these observations using the initial (X, Y, Z) composition (0.602, 0.354, 0.044) and assuming the stars to have formed uniformly over a period of 1.5 × 107 years about a mean age of 5.75 × 107 years. Although she was able to fit the luminosity and effective temperature spread of the red giants, her theory predicted far too many stars at the bottom of the red giant branch relative to the number of bluer giants.

This paper is a preliminary report on the sky mapping being undertaken at the University of Tasmania using the Llanherne low frequency array. (Ellis 1972).

The observations are facilitated by the use of an on-line PDP-8 computer and the beam steering system described by Whitham (1975). In summary, a scanning system is used in which the computer is programmed to steer the telescope beam to a number of declinations with a time interval between settings such that a scan takes 5 minutes. Usually a scan of 12 declinations is chosen. Calibration levels obtained each hour and recorded on magnetic tape permit gain changes to be accounted for when the data is analysed from the tape.

Large solar radio outbursts at metre wavelengths often consist of a group of type III bursts followed a few minutes later by a type II burst; in both spectral types the intense burst radiation drifts towards lower frequencies with time (Figure 1).

For many pulsars the integrated or mean pulse profile is highly polarized. Generally linear polarization dominates over circular and there is a continuous variation of position angle through the profile (e.g. Manchester 1971). In most models for the emission process the angle of polarization is related to the (projected) direction of magnetic fields in the source region. Several of the observed properties of pulsars, for example, the mode-changing phenomenon (Backer 1970) and the different spectral index of different components of the intergrated profile (Manchester 1971), suggest that different parts of the integrated profile are emitted in different (though closely related) parts of the source. The different observed position angles across the integrated profile would then result from different projected magnetic field directions in these different parts of the source. For many pulsars the observed position angle variations are closely represented by a path through a radial set of projected field directions such as would be obtained in the vicinity of a magnetic pole (cf. Radhakrishnan and Cooke 1969).

Any theory dealing with type IV solar radio bursts must explain the observed evolution of their brightness temperature and polarization. The behaviour of isolated, moving type IV sources is characterized by a long period of constant and low polarization during the major part of their lifetime, followed by a substantial increase in the degree of circular polarization during the declining phase. This behaviour puts severe constraints on and gives valuable clues as to the evolution of the physical conditions within the source.

The basic observational evidence for helium-burning red giants in open clusters has been given elsewhere, and I shall give here only a summary and then describe in more detail new results for one cluster, NGC 2477.

Observations for the Parkes 2700 MHz catalogue are carried out in two stages: (i), a relatively fast finding survey, followed by (ii), accurate measurement (at 2700 MHz) of flux densities and positions of the sources on the survey scans. For the first six parts of the catalogue intervals of several weeks between the stages resulted from the necessity to reduce the (analogue) survey scans manually. This communication describes a computer program which records and reduces these scans, and which produces an on-line map and source listing for the survey region. Thus the measurements of the second stage may be carried out immediately after the survey; additional advantages provided by the technique are discussed later in the paper.

Extensive air showers radiate because they are essentially sheets of charge moving through a medium at relativistic velocities. Of interest in the present experiment are their emissions in the optical and radio regions of the spectrum—the first long accepted as primarily of a Cerenkov origin, and the second very far from fully understood.

Evidence has been mounting for some years that cosmic rays have a dwell time in the disk of the Galaxy of 106-107 years. This evidence comes mainly from the study of the chemical composition of the cosmic rays, for if the particles were stored in the Galaxy for a longer time the heavy nuclei would suffer more collisions with interstellar matter and would be broken down into lighter nuclei or protons (see, for example, Shapiro).

The purpose of this paper is to advance an alternative hypothesis for the underlying distinction between solar radio bursts of spectral type V and ‘inverted U’ bursts, and to explore its implications.

In the preceding paper, Cannon has outlined the observational evidence for the existence of a distinct concentration of stars near the base of the red giant branch in intermediate-age galactic clusters, which he tentatively identifies with the core helium burning phase of evolution occurring after the helium flash. This paper reports preliminary results of evolutionary calculations to test this identification.

Since the computation of hydrogen shell-burning evolution up the red giant branch is extremely time-consuming, the present calculations have been commenced at the stage immediately following the helium flash. It is assumed that no overall mixing occurs at the flash, so that the composition discontinuity at the hydrogen-burning shell remains sharp. The initial stellar composition was set at (X, Y, Z) = (0.68, 0.30, 0.02), corresponding to Population I material.

Since early 1974 the radioheliograph operated by the Division of Radiophysics at Culgoora, N.S.W. has been used in a 160 MHz study of ~2000 catalogued sources in the declination range -46° to +35°. In addition to measurements of flux densities and accurate positions at 160 MHz, brightness distributions are obtained for the sources that can be resolved by the 1’.9 × 1’.9 arc beams. A comparison of the brightness distributions at 160 MHz with those obtained from high-frequency measurements with similar angular resolution can yield valuable information about the energy distribution of the relativistic electrons, which are believed to be responsible for the radio emission from most nonthermal sources. Among the first objects to be examined were the strong southern radio galaxies Centaurus-A and Pictor-A.

Free-free absorption by thermal electrons attenuates low frequency radio waves and such absorption will indicate the presence of ionized hydrogen. The Gum Nebula contains bright H-alpha emission regions and therefore it is not surprising that the region appears as an area of low brightness on low frequency continuum maps.

In a previous paper it was shown how one could improve upon the Böhm-Vitense model of the solar convection zone by the inclusion of four different length scales and by the determination of these length scales with the use of the quasi-Vitense model as developed by Unno. In this way the vertical wave number kz, associated with a characteristic eddy, can be determined by the integration of a second order differential equation. The integrations have to be started at a suitable depth and all model calculations depend critically on the assumed structure of the top layer.

The accepted interpretation of the low frequency turnovers in the spectra of many extragalactic radio sources is that they are due to the effects of synchrotron self-absorption, i.e. to the source becoming optically thick. It has been shown that the signs of the degrees of both linear and circular polarization for a homogeneous source at frequencies where it is optically thick are opposite to those at frequencies where it is optically thin.