This paper examines recent investigations of emission-line filaments along the edge of the radio source in Centaurus A. It shows how these studies have ramifications for the excitation of the narrow line regions and extended emission-line regions of other active galaxies.

At the first A.S.A. meeting in 1966 radio astronomers knew of only the 21 cm line of hydrogen, a handful of hydroxyl lines and some radio recombination lines. The number of molecular lines now known in the radio spectrum is close to 220, so radio spectroscopy has become a fully fledged subject. I shall not discuss here the recent ultraviolet studies of H2, HD and CO molecules that have been reviewed by Spitzer and Jenkins (1975).

We have carried out an extensive survey of Hα emission stars in the Orion region over an area of about 100 deg2. We present the results for the areas A-0975 and A-0976 of about 25 deg2 each.

Observations of the 21 cm line of neutral hydrogen can provide several integral properties of galaxies. The systemic velocity Vsvs indicates the distance Δ via the Hubble relation or through group membership. The integral over velocity of the flux density profile, ∫S dV, immediately yields the amount of neutral hydrogen in the galaxy: M H ∝ Δ2∫S dV (neglecting optical-depth effects). The profile width W and the inclination i (derived from the optical axial ratio), together with the (optical) angular diameter a, supply the ‘indicative mass’ Mi ∝ (W/sin i)2 a △ (Bottinelli et al. 1968; Balkowski 1973), which is a fair estimate of the total mass of the system. In addition, as shown by Tully and Fisher (1976), the profile width is a good indicator of luminosity L. The quantities and L, which are (at least roughly) representative of the amounts of matter and of gaseous and luminous material in the system, give an indication of its composition. Together with the linear diameter a△, these quantities contain clues as to galaxy formation and evolution.

The results of a new imaging survey of 68 bright (mv < 18) high redshift (z > 0.7) quasars are presented. The distribution of celestial distances between the quasars and the nearest galaxy neighbours shows an excess at small separations (< 15 arcseconds) significant at the 99.96% level. The redshifts of these galaxies are not known, so two interpretations are possible. If the galaxies are in groups physically associated with the quasars then they must be significantly brighter (> 3 magnitudes) than normal M* galaxies at the present epoch. Alternatively, this may be the result of a bias caused by gravitational amplification of background quasars by compact lenses in the halos of the nearest neighbour (foreground) galaxies. Of the present sample, 25% of the quasars have extra galaxies. If this is caused by a gravitational lensing bias, then, allowing for incompleteness, the results imply that as many as 60% of bright quasars may be gravitationally lensed.

A nearly stationary pulsar wind is shown to be always collimating along the direction of rotation. It follows that the conventional picture of the equatorial pulsar wind can occur only in a highly time-dependent manner, which, if true, may account for the observed time variation within a single pulse. Furthermore, a mechanism, via excitation of magnetosolitons, is proposed for explaining the continuous generation of energetic electrons, which yield the observed radio emission in the Type II supernova remnants. Fully relativistic analyses will be presented to substantiate these claims.

A major requirement of modern radio astronomy is the attainment of the highest possible angular resolution. This high angular resolution should be matched by a high sensitivity and by spectral and polarization capabilities. Study and experience have shown that no form of telescope is more effective in this respect than the aperture synthesis type. The past few years have seen a growing realization amongst astronomers, both here and overseas, of the need for a new synthesis telescope able to observe the full southern sky. This realization has been stimulated by several factors:

The origin of QSO redshifts is an important problem for which there is still no definite answer (Burbidge 1979). Recent observations by Walsh et al. (1979) of what is probably a gravitational lens associated with the twin QSO’s 0957+ 561 A,B offers the possibility of testing whether the redshift of the QSO involved is cosmological in origin. In general, if a gravitational lens is responsible for splitting the image of a QSO into two or more distinct components, it is possible to calculate the redshift of the QSO provided we have enough observational data involving the lens. The calculated redshift must then be consistent with the observed redshift if it is entirely cosmological in origin. The quantities that must be observed before the redshift can be calculated are the differences in the light travel times along the different paths from the QSO to us, the redshift of the lens, the angular separation of the images, and their relative intensities.

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.

Much of the information regarding the nature of solid particles in interstellar space has been gained through the study of the line-of-sight extinction of starlight and the polarization of starlight by these particles. Study of the optical properties of these particles can be extended through consideration of the scattering of stellar radiation in reflection nebulae. This type of approach requires the adoption of models for the star-nebula system, and the grain type to be considered. These models are then used in a theory which describes the scattering of light by an ensemble of small particles, as applied to dust nebulae. Results are thus obtained for the colour of the nebula as a function of distance from the illuminating star. These results can then be compared with the corresponding results of experimental broad-band photometry.

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.

Two recent observational surveys of the Ca II resonance lines (Zarro and Rodgers 1983; Linsky et al. 1979) illustrate the great diversity of line profile shapes found in the spectra of cool stars. This diversity reflects a corresponding wide range in the underlying chromospheric properties of the stars. There are, however, three well-marked systematic trends in the shapes of Ca II line profiles which presumably reflect systematic trends in chromospheric properties. One of these, the Wilson-Bappu effect (Wilson and Bappu 1957), describes the strong correlation betweeen the width of the emission core (see Figure 1) and the absolute visual magnitude of the star. Despite much work, it is still not clear whether this is due primarily to systematic changes of velocity fields (e.g. Hoyle and Wilson 1958) or optical depths (e.g. Jefferies and Thomas 1959) in stellar chromospheres.

In view of the already available reviews on the subject, the progress after 1972 is summarised. Newly identified species and molecular transitions are listed. How the studies of solar molecules can be helpful in understanding the solar atmosphere, in structuring better models and in deriving molecular parameters with some degree of confidence, is stated.

MM-(millimetre) wave astronomy offers over one hundred gigahertz of explorable spectrum within which the transitions of a large number of important molecules occur. Some of these molecules are as simple as carbon monoxide while others are as complex as trans-ethyl alcohol and methylamine; the former species are widely distributed in the Galaxy while the latter species are more localized in extent.

The five major members of the Sculptor Group of galaxies and NGC 45 have been observed with the Molongloobservatory synthesis telescope. NGC 247 and NGC 300 were not detected and upper limits to their 843 MHz flux densities are given. Radio emission from NGC 7793 is discussed with particular attention to its morphology, radial dependence compared with that of the blue light and possible coincidences between HII regions and 843 MHz peak flux densities.

Observations of the relative positions of fundamental and second harmonic bursts can be used to study refraction and scattering effects in the corona. Smerd, Wild and Sheridan have pointed out that the observed positions of type II bursts can be interpreted as favouring the backward emission of the second harmonic in a smooth corona. In this case the harmonic is seen after reflection from near the fundamental plasma level. Several other examples of type II and type III bursts have been reported which show this effect. We wish to present further evidence from a recent study of a large number of type III bursts observed with the 80 MHz heliograph and 158 MHz interferometer.

The complex flare related events taking place in the solar corona are becoming better understood as more observations are made with high spatial and temporal resolution nearly simultaneously at widely separated radio frequencies. Similarly the magneto-plasma structures related to the so-called quiet Sun, which have been extensively studied during the recent cycle (No. 20), are now better understood because of such high resolution observations.