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.

The past and present existence of smaller bodies in our solar system manifests itself in various ways through the appearance of asteroids, minor moons, planetary rings, surface cratering, etc. The occurrence of these planetesimals appears to be an integral intermediary step in the formation of the larger bodies from the initial grain state. In order to account for the discreteness and order of the planetary orbits and regular satellite systems, Prentice (1977, 1978) has suggested that the accumulation of this planetesimal material took place in a series of well defined orbits corresponding to the positions of a system of gaseous Laplacian rings that were shed by the primitive contracting parent cloud. Alfvén and Arrhenius (1975) have also drawn attention to the fact that planetesimal formation occurs far more effectively if the accumulation takes place along well defined ‘jet streams’. Hourigan (1977) has previously demonstrated how such concentrated rock/ice streams or ‘jet-streams’ naturally form on the mean Keplerian orbit of gaseous rings that are present in the Prentice-Laplace model.

We have used the Parkes 64m telescope to observe the 20 → 3−1E absorption of CH3 OH at 12.2 GHz towards 58 Galactic H II regions and dark clouds, yielding 38 detections. The results show that CH3 OH absorbing clouds have a typical optical depth of 0.25 and a column density of 8.4 × 1015 cm−2. CH3 OH absorption is often accompanied by unsaturated maser emission and is closely associated with background H II regions. CH3 OH absorption against the 2.7 K background is also observed in several dark clouds.

In 1961 Fokker and Roosen suggested that the concept of homology as applied to solar optical flares by Ellison, McKenna and Reid could be extended to flare-associated radio events as well, since successive flares within the same centre of activity sometimes produce radio bursts which look remarkably similar on single-frequency records. Teresa Fortini reported very similar ionospheric responses due to X-radiation from flares recurring in the same active region. In 1950 Wild noted similarities in the dynamic spectra of type III bursts occurring within periods of minutes.

Duley (1974) has shown that, at the temperatures usually associated with interstellar gas clouds, we would expect CNO grains to be present. During gravitational collapse these grains migrate to the centre of the gas cloud, leading to an enhancement of the heavy-element abundance in the core (Prentice 1976, 1978). It was Krautschneider (1977) who verified such a scenario, by considering the dynamical collapse of gas and grain clouds. If such an initial radial abundance inhomogeneity existed, Prentice (1976a) showed that this configuration may well survive the later convective mixing phase and thus approach the zero-age main-sequence (ZAMS) with a small (-v 3% by mass) metal enhanced core.

The deflection of the light rays of a distant star by the gravitational field of a nearby star was first derived independently by Link (1936) and Einstein (1936). It was shown by Link (1936,1937) that the light of a distant star is not only deflected forming two separate images of the distant star, but also the brightness of the distant star (in bothimages) is affected.

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 current ephemerides include an allowance for umbral oblateness based on the flattening of the Earth’s geodetic reference spheroid; there are few published estimates for umbral oblateness derived directly from the geometry of a lunar eclipse. This paper reports umbral oblateness values which have been derived from 7,400 crater contact timing observations of twenty-one lunar eclipses by amateur and professional astronomers since 1972. The observed umbral oblateness was found to be typically three times the geodetic reference spheroid flattening.

Very few (if any at all) three dimensional models of the final evolutionary stages of a star’s life have appeared in the literature. Such models may be important if the stellar core maintains sufficient rotational energy during it’s lifetime so that when collapse finally occurs, the increase of rotational energy to gravitational energy, may lead to a non-axisymmetric instability.

A sequence of core collapse models with decreasing rotation rate is considered. These models were calculated using a three dimensional, post-Newtonian, hydrodynamical, numerical code. The results show that for high precollapse rotational energies the core can become unstable resulting in the formation of what resemble ‘spiral arms’. Unfortunately, because of limits on computer time, the calculations had to be discontinued shortly after this development occurred.

We describe a method for reducing displacements in radio source positions caused by ionospheric refraction. Our method is an improvement on that used by Wild et al. (1959), who assumed all frequencies in the 40-70 MHz band came from the same position above the Sun and applied an f-2 correction for ionospheric refraction. Our method retains the dispersion of source position with frequency, which is inherent in the radio source, but allows for the f-2 ionospheric effect. We also discuss ways of estimating the absolute source positions from a knowledge of ionospheric density gradients. A typical example of ionospheric variations on solar records is shown in Figure 1(a). Here we have plotted the observed source positions on an f-2 scale. The measurements refer to a solar storm continuum burst which occurred on 1981 May 9 following an importance 2B flare at 08°N., 38°E., heliographic coordinates. From previous observations of such events we think it highly likely that the true source positions are stationary and displaced with decreasing frequency outwards along a line close to the radial direction above the flare. Figure 1(a) shows that: (a) the 160, 80 and 43 MHz source displacements vary as f-2 ; (b) there is a systematic slow drift of the source positions towards the south and east which increases with increasing hour angle; (c) superimposed on this steady drift is a quasi-periodic variation in source position with a period ~20 min.

Hodge 11 (= SL 868) is a red, globular-like cluster (V ≅ 12.1, B—V = 0.62), situated on the east side of the LMC about 5 kpc projected distance from its centre (Gascoigne 1966). It was included in a programme to study the chemical evolution of the LMC by determining ages and metal abundances for a number of its clusters. Figure 1 shows a preliminary colour-magnitude diagram, found from four AAT plates calibrated with the AAT two-channel photometer. The choice of the radius, 1′.37 (23 pc), within which the stars were measured, was guided by the surface photometry of the cluster described later (Figure 3). But while it makes the number of “clean” stars inside the radius rather small, those outside it are too unlikely to be cluster members. As yet the calibration extends only to V = 19.6, and the nature of the cluster cannot be determined unambiguously. But Figure 1 already shows an unusual feature, in the very blue colour of the group of stars at V ≅ 19, B—V = 0.60, which on the usual interpretation would point to a metal abundance possibly lower than any yet encountered.

The Cross radiotelescope at the Molonglo Radio Observatory (Mills et al. 1963) came into full operation during 1967 and observations continued without interruption until 1978 when it was closed down for substantial modifications; these are now largely complete and observations have re-commenced. The decision to make some drastic changes was taken about seven years ago, although it had been evident right from the beginning that scientific returns from the Cross would drop sharply once the whole accessible sky had been surveyed. Indeed, the specifications for the original instrument were chosen to permit a subsequent conversion from 408 MHz to 1420 MHz with little extra expenditure on the reflector structure. Also, in 1972 a new form of circular polarized antenna was developed to provide a cheap mass-produced feed for 1420 MHz operation which could be easily phased and had good directional properties (Mills and Little 1972).

The three objects Tau X−1, Cyg X−l and GX3+1 are the most prominent discrete X-ray objects in the sky at photon energies of ≃ 100 keV.

Variation of the electric current profile as a means of energy release in a solar flare is investigated. In particular, the change in magnetic energy is calculated for some simple idealized cases of the current profile. It is suggested that current profile changes may explain the smallest observed energy release structures in a flare.

The non-linear modal equations governing magnetoconvection in a fluid layer have been integrated forward in time incorporating a discrete spectrum of horizontal wave numbers, distributed within the range supporting convection. By progressively deleting some of the decaying modes and introducting additional modes within the range of growth it is possible to establish the evolution, or otherwise, of a preferred horizontal scale, which determines the horizontal cell size of the convective motions. Further, the influence of the magnetic field strength on cell extent can also be determined.

On July 14, 1982 a Forbush decrease event of unprecedented magnitude was observed worldwide in the cosmic ray records up to particle rigidities of several hundred GV. At the same time the recently commissioned underground proportional counter telescope at Mawson, Antarctica, was recording a newly discovered cosmic ray modulation superposed on the Forbush event (Duldig, Jacklyn and Pomerantz 1985; Jacklyn, Duldig and Pomerantz 1987). The presence of the two phenomena led to complication in deriving the spectrum of the Forbush decrease for particle rigidities corresponding to the shallow observing depth. A technique for resolving such difficulties is presented and applied to the July 1982 decrease and the recurrence event 27 days later. The resulting spectral index γ was found to be ≈ −0.9, similar to the results of the extensive analysis of Russian surface and underground data by Kuzmin et al. (1983).

Most of the known 1.35 cm water vapour masers have been detected in the direction of known 18 cm OH masers. However, a small number have been found in the direction of HII regions where no OH maser is known. Several new examples of H20 masers with no known OH counterparts have recently been published by Kaufmann et d. (1976), who suggest that these constitute a new class of H20 maser.