During recent years a firm relationship has been established between disappearing solar fragments and geomagnetic disturbances (Joselyn and McIntosh 1981; McNamara and Wright 1982; Wright and McNamara 1983). Wright and McNamara (1983) showed that the average magnitude and delay of the geomagnetic disturbance depended upon the size of the filament.

The close association between flare events having metric radio type II and type IV bursts and the subsequent occurrence of sudden commencement geomagnetic storms is well known. In such cases it has been amply demonstrated (e.g. Malitson et al. 1973; Cane et al. 1982) that the sudden commencement (SC) is caused by the same magnetohydrodynamic shock which originates near the Sun and which produces the type II burst. Recently, a study of geomagnetic storms thought to be associated with the disappearance of filaments from quiet regions of the Sun (Joselyn and McIntosh 1981) showed that several of these storms began with marked sudden commencements.

Plasma loops are the dominant structures, in the higher levels of the Sun’s atmosphere above active regions. Much of our knowledge of their properties has come from space observations made over the past decade or so in the EUV and X-ray regions of the spectrum and, more recently, from high-resolution, two-dimensional images of microwave sources obtained with the Very Large Array radio interferometer (VLA). On the other hand, the spatial resolution of rocket and satellite observations has so far generally failed to match that of ground-level optical observations made in Hα and other strong chromospheric lines. The latter permit one to study in much greater detail the morphology of individual loops, as illustrated for example in the recent work of Loughhead, Wang and Blows (1983). These authors addressed themselves to the task of determining the true geometrical shapes of individual loops, a problem which had hitherto received little attention.

Radiation generated in the solar corona can be drastically altered by refraction and scattering as it escapes. This is especially true for sources having a frequency near the local plasma frequency, where the index of refraction approaches zero. Early investigations of the problem (e.g. Fokker 1965; Steinberg et al. 1971; Riddle 1972, 1974) have shown that the size, shape, location, intensity and time profile for the observed source can all be influenced.

Since its discovery by Haro (1952) the star H1-36 has been catalogued as a planetary nebula despite its extremely high-excitation emission-line spectrum (e.g. [Fe VII], [Ne V]) and its imposing, variable infrared excess. Because its optical spectrum resembled those of many symbiotic stars, I have persistently classified H1-36 as such. A meaningful definition of a symbiotic star would necessarily include both the high-excitation emission-line spectrum and the presence of a cool (usually M-type or Mira) giant.

Baade (1963) pointed out three regions of low obscuration in the general direction of the galactic centre, wherein a stellar population assumed to be characteristic of the galactic bulge could be studied.

The nature and cause of the double-mode (DM) pulsation in beat Cepheid variable stars is still a matter of considerable uncertainty. Recently, evidence has been accumulating that the relative energy of the two modes in any particular star may be a slowly varying function of time. For TU Cas, Hodson, Stellingwerf and Cox (1979) have found that the first overtone amplitude has been decreasing over a 67 year timebase, while the present authors (Faulkner and Shobbrook 1979) have reported an increase in overtone energy in U TrA over 20 years. Observational details of the form of the mode energy changes may be helpful in obtaining a better understanding of these stars (see Shobbrook and Faulkner 1982). Our present observations of U TrA have been obtained to investigate its energy changes more fully.

HD 44179, a ninth-magnitude star of late B spectral type, is peculiar in several respects. At red wavelengths it appears to be located at the apex of a biconical nebular (‘The Red Rectangle’) of dimensions about 1′ arc. Cohen et al. (1975) identified the system with the bright infrared source AFGL 915 and carried out investigations at optical, infrared and radio wavelengths. The complexities of the spectra have continued to interest astronomers.

Although the radio continuum distribution of the HII-region/molecular-cloud complex W33 (peak l = 12°.8, b = -0°.2) resembles a discrete region about 15′ arc in size, the behaviour of the recombination-line velocities (Gardner et al. 1975; Bieging et al. 1978) and molecular-line velocities (OH: Robinson et al. 1970; H2CO: Gardner and Whiteoak 1972) has been difficult to interpret in terms of a simple model. There is a difference of opinion as to whether W33 consists of two independent complexes at different distances along the line of sight or a single expanding complex (e.g. Goss et al. 1978).

We present the initial results of a statistical comparison of CO emission and H I self-absorption in the galactic plane at large distances from the Sun. Evidence for self-absorption by cold atomic hydrogen (Ts < 60 K) over angular scales of 3 ´-20´ was reported by Baker and Burton (1979). They suggested that this hydrogen was associated with the molecular clouds of the ‘molecular ring’ located between 4 and 8 kpc from the galactic center (Burton and Gordon 1978). Burton, Lizst, and Baker (1978) did find a correspondence between CO emission and H I self-absorption; however, their observations were not extensive enough to prove that the correspondence was statistically significant or to test their prediction that all instances of H I self-absorption are accompanied by CO emission and thus associated with molecular clouds.

High-resolution radio maps of supernova remnants (SNRs) are indispensable for distinguishing the more common shell remnants from the centrally concentrated (Crab-like) remnants; such studies also reveal any departures from symmetry, and this can yield vital information concerning interaction of the ejecta with the surrounding interstellar medium.

The space density of degenerate stars is an important parameter in Galactic Structure studies, not only because white dwarfs represent a significant fraction of the local mass density, but also because they act as tracers of the history of star formation (see e.g., Bessell 1978). Combining the present day luminosity function with theoretical cooling tracks allows constraints to be set on the birth rate of main sequence progenitors. However, since white dwarfs are intrinsically low luminosity objects, observational studies are hampered by difficulties in defining complete samples large enough to have statistical significance. This paper discusses preliminary results from one method of tackling this problem.

Star formation is believed to occur in interstellar clouds consisting of both gas and grains. Under the gravitational influence of such a cloud the constituent dust grains sediment toward the centre, and both calculations and implications of this sedimentation have been published by many authors (McCrea and Williams 1965; Horedt 1973, 1976; Prentice 1976; Krautschneider 1977; Flannery and Krook 1978; and others). Two main results from these calculations warrant our attention. Firstly, the timescale for appreciable sedimentation Ts ≃ 107 -108 years, which is consistent with age estimates of many clouds (Harrison 1978, Blitz and Shu 1980). Secondly, the sedimentation proceeds more rapidly for larger grains. This leads to an increase of mean grain size toward the centre of the cloud.

NGC 253 is the major member of the Sculptor group of galaxies. It is classified SAB(s)c by de Vaucouleurs, de Vaucouleurs and Corwin (1976) and is almost edge-on. Previous studies have revealed a peculiar velocity field near the nucleus (e.g. Ulrich 1978). The nucleus is also a moderately strong radio and infrared source (Beck et al. 1979, Klein and Emerson 1981, Elias et al. 1978, Telesco and Harper 1980, Rieke et al. 1980).

The Magellanic Clouds are the nearest major extragalactic objects to the Milky Way. The study of young giants or supergiants in the Clouds enables us to obtain information regarding the birth rates and evolution of young massive stars in those systems, free from biases inherent in similar studies in the Galaxy. Although the Magellanic Clouds have been studied by an extremely large number of research workers at optical wavelengths, it is only recently that significant infrared observations have also been undertaken (e.g., Glass 1979, McGregor and Hyland 1981, Cohen et al. 1982). Cool supergiants in the SMC have been studied optically by Humphreys (1979). She found that most are very metal deficient, and should be classified spectroscopically as M0.

NGC 5128, identified with the radio source Centaurus A by Bolton et al. (1949), is a remarkable galaxy which appears to consist of an elliptical or SO galaxy crossed by a strong dust lane. The early idea that this represented a pair of colliding galaxies (Baade and Minkowski 1954) powering the extended double radio source fell out of favour but has recently been revived (Malin et al. 1983) in the light of extensive kinematic evidence. However, the interpretation of the data is not yet complete, and it has also been suggested recently that NGC 5128 is really a spiral galaxy with a spectacularly large bulge (Marcelin et al. 1982).

While Centaurus A (NGC 5128) is not a particularly powerful radio galaxy, its proximity (˜ 5 Mpc) permits us to obtain linear resolution an order of magnitude better than can be obtained for the more powerful, distant radio galaxies. Thus one can hope to make meaningful comparisons between the morphologies seen over the electromagnetic spectrum from γ-rays to metre waves. This should lead to a more complete understanding of the energy production mechanisms and evolutionary histories of these objects.

PKS 1318-43 was first identified with the elliptical galaxy NGC 5090 by Ekers (1969) in the Parkes catalogue. Schilizzi and McAdam (1975) mapped the source with 2.9 arcmin resolution at 408 MHz using the Mills Cross, resolving the source into an extended double structure approximately 15 arcmin in extent at p.a. 36°. Schilizzi (1975) also noted a possible optical link with an edge-on spiral (NGC 5091) ~75 arcsec to the south-east. Figure 1 shows a print of the two galaxies taken from the UK Schmidt J survey film. During 1980, in collaboration with K. J. Wellington, RMS mapped the source at 1415 MHz with the Fleurs Synthesis Telescope (FST, Christiansen 1973).

There are many thousands of photographic star plates in observatories throughout the world, and the number is being added to continually. A major difficulty in making use of the information contained in them lies in the measurement of position, and other data, of star images on the plates, and in bringing the data to a form suitable for computer processing. Manual methods are impossibly slow and laborious for an extended program of measurements, and automatic machines on the market are prohibitively expensive for small observatories with limited resources.

The polarization characteristics of celestial radio signals are a major part of the observable nature of the radiation. Stokes polarimeters, instruments for measuring the complete polarization properties of radiation, are usually narrowband devices in order to minimise depolarization effects originating in the source or in the medium through which the radiation propagates. To measure the broadband polarization behaviour of a source, a Stokes polarimeter-spectrometer is required. Such an instrument allows the frequency dependence of each Stokes parameter to be deduced, making it possible to apply corrections to each parameter to account for known forms of polarization distortion (e.g. Faraday rotation). It is also possible to remove delay distortion from impulsive sources such as pulsars by processing the spectrometer data according to the usual de-dispersion algorithms. In some studies observation of distortion phenomena may be the major aim and a polarimeter spectrometer greatly facilitates measurements of these effects.