The basic system of differential equations governing the non-radial adiabatic oscillations of stars are given in the review article by P. Ledoux and Th. Walraven. The numerical integration of these equations has been undertaken by P. Smeyers and by R. Van der Borght and Wan Fook Sun, in the latter case for stars of uniform composition in the mass range.

where μ is the molecular weight of the stellar material. These integrations were based on models derived by R. Van der Borght.

For some years now, there have been suggestions that the nuclei of planetary nebulae are stars undergoing a final gravitational contraction to the white dwarf state. These have culminated in two important studies by O’Dell, and by Seaton and his collaborators, the results of which are indicated on the Hertzsprung-Russell diagram of Figure 1. The temperatures and the distances—and hence luminosities—of the central stars are obtained from flux observations of the stars themselves and the surrounding nebular shells, the former by the Zanstra method, and the latter by that of Shklovsky.

A search for the 126a hydrogen recombination line, with a rest frequency of 3248.713 MHz, has been made in the 19 sources listed in Table I using the Parkes telescope. The beamwidth was 6′ are and the frequency resolution 37 kHz. In the Table RCW refers to the Rodgers, Campbell and Whiteoak Atlas, W to the Westerhout catalogue, and the co-ordinate numbers to the Parkes Catalogue of Sources. In each case the ratio of the peak of the line to the continuum TL/TC, the half-intensity width Δv and the mean radial velocity to the local standard of rest, were determined. The related velocities observed in OH emission and absorption are also shown.

Thirty-one radio sources have been investigated for the presence of OH-line radiation in their directions. Absorption and anomalous emission lines were observed.

The equipment and methods of observation have been described by Gardner, McGee and Robinson (1967). An aerial beamwidth of 12’.5 arc was combined with a 48-channel line receiver of bandwidths 37 and 10 kHz.

The high intensity anomalous OH emission which has been detected in the neighbourhood of HII regions exhibits remarkable polarization characteristics, narrow spectral features, and unusual ratios of line strengths. All of these unusual properties are generally believed to be attributable to maser action of some form. A knowledge of the structure of the emitting regions and their brightness temperature is necessary for the development of a satisfactory theory of the emission mechanism.

Results of recent surveys of high velocity HI clouds with the 80-ft reflector at Dwingeloo and with the 260-ft x 80-ft standing paraboloid of the Ohio State University are combined. They show that clouds with high negative radial velocities occur mainly in the longitude range 50° to 220° from N. to S. galactic poles. However, nearly three times as many clouds are found north than south of the galactic plane. Clouds with high positive radial velocities are much less numerous than the negative velocity clouds. They have been found between longitudes 260° to 350° and scattered around lII = 75°, bII = +45°.

Survey type observations have been made with the Parkes radio-telescope of 4 galactic radio sources having either a non-thermal radio spectrum, or exhibiting shell structure in their emitting regions. Observations were made at a wavelength of 11 cm using the Parkes radiotelescope where the beamwidth is about 7.5 min.arc.

Observations of the composite radio source which includes the catalogued components 1209-52 and 1209-51 (Bolton et al. 1964) have been obtained at frequencies 629, 1410, and 2650 MHz with the 210-ft Parkes telescope. The observations at the highest frequency are shown in Figure 1. The isotherms of full-beam brightness temperature correspond to the single polarization direction shown within the circle representing the half-intensity beamwidth. The polarization vectors (unbroken lines) along the two ridges represent 15-25% linear polarization. The intrinsic angles of polarization, derived from the 1410 and 2650 MHz observations, are represented by the broken lines. They are perpendicular to the magnetic field if the radiation is synchrotron. The corresponding rotation measures (Gardner and Whiteoak 1963) range between +17 and +36 rad. m-2 along the eastern ridge, and between —14 and —4 on the western side.

Photometric observations on the UBV system have been made of a number of optically identified radio sources. The measurements are basically of two types: (1) offset photometry with the Siding Spring 40-inch reflector of objects identified as probable quasars or N galaxies, and (2) observations with the Siding Spring 24-inch reflector of radio galaxies brighter than V = 14m.0.

High resolution studies of clusters of galaxies at radio frequencies may contribute substantially to our knowledge of the properties of radio galaxies, their evolution and their luminosity function. A considerable amount of statistical information is already available on the correspondence of radio sources and clusters; the present investigation is aimed rather at a detailed examination of the sources and their identification with actual galaxies or other objects.

Over the past three years, using the Parkes Telescope, accurate positions of over 700 extragalactic radio sources have been obtained for the purpose of optical identification of the sources.

These observations have been made with the 210ft-60ft variable baseline interferometer at the Australian National Radio Astronomy Observatory.

Figure 1 shows the spectrum of 3C279 (1253-05) in mid-1966 derived from observations at frequencies of 467, 630, 960, 1410, 2650 and 5000 MHz made by Batchelor, Brooks, Cooper, Milne, Roberts and the author with the CSIRO 210 ft. telescope. The figure also shows the spectrum obtained in 1964 by Kellermann with the same telescope. All the flux densities have been measured relative to a number of calibration sources on a scale previously determined by Kellermann. Although our flux densities are preliminary, further analysis should not change them significantly.

Although the synchrotron emission from a single electron moving with an ultrarelativistic velocity βc in a magnetic field B0 is elliptically polarized, the characteristics of the polarization ellipse being determined by the position of the direction of observation n relative to the cone swept out by the direction u of the velocity vector about the direction of B0, the resultant emission from a distribution of such gyrating electrons is, to a first approximation, linearly polarized in the direction perpendicular to the projection of B0 on to the plane transverse to n. The reasons for this are that for a single electron the emission is effectively confined to within a small angular distance O(ξ) of u, where ξ = √ (1 −β2) ≪ 1 and that (i) the fourth Stokes parameter is to this approximation an odd function of the angle ip between n and u at its closest approach, and (ii) the number of electrons passing within equal angular distances ψ = ±O(ξ) are equal. It follows that if ξ is large enough it is possible for the next approximation to the fourth Stokes parameter for a distribution of electrons to be significant, so that the resultant emission is elliptically polarized.

Balloon borne alt-azimuth mounted X-ray telescopes flown from Hyderabad, India (17°N), Palestine, Texas (32°N), and Mildura, Australia (34°S), have detected hard X-rays (hv>20KeV) from discrete sources in the Cygnus region.

In the field of cosmic ray galactic studies, two kinds of phenomenon are currently being investigated by members of the Hobart cosmic ray group, led by Dr. A. G. Fenton. In a combined project with the University of South Australia, the University of Tasmania is participating in an experiment whose aim is to locate sources of galactic X-rays in a part of the southern sky inaccessible from the northern hemisphere. The object of the other investigation, which forms part of a joint ANARE-University programme of cosmic ray research, is to elucidate the evidence for intensity maxima from fixed galactic directions in the otherwise isotropic charged primary radiation.

Instruments were flown on the Pioneer 6 and 7 spacecraft during 1965-66 to study the degree of anisotropy of cosmic radiation in the energy range 7.5-90 Mev/nucleón. The instruments record the cosmic ray fluxes from each of four contiguous ‘quadrants’ of azimuthal rotation of the spacecraft, for each of three energy windows 7.5-45 Mev, 45-90 Mev, and 150-350 Mev for alpha particles and heavier nuclei. In addition, the counting rate of all particles of energy >7.5 Mev is recorded, thereby providing cosmic ray data of high statistical precision useful in the study of fast changes in the cosmic ray flux.

The Parkes Interferometer was designed and constructed by the CSIRO Radiophysics Laboratory. It is unique in having continuously variable North-South and East-West baselines making possible plotting the visibility function of a source in a single observation. From an engineering point of view it is noteworthy in that the receivers, control circuits and computer employ semi-conductors exclusively.

The usual method of calculating corrections for precession nutation and aberration involves the use of the precession constants M, N, m, n and the Day Numbers A, B, C, D, E, J, J’. For the computer analysis of radio source data obtained with the Molonglo Telescope it seemed desirable to compute the corrections directly from the basic formulae, thus avoiding the trouble and possibility of accidental error in copying out the Day Numbers for each day’s observation. In this paper we quote in full the equations that are used in the analysis of the Molonglo data. These equations are abstracted from The Explanatory Supplement to the Astronomical Ephemeris and Smart’s Spherical Astronomy, and expressed in a form which parallels the organization of the computer routine. In addition to the observed position, the only other data required to compute the precession nutation and aberration corrections is the Julian date (J.D.). This basic parameter in the equations is very simply calculated to the required accuracy of a few minutes from the time and date of the observation. The computer routine that computes the corrections occupies 1350 words of programme in the KDF9 computer and takes 200 msec to compute one position. If a large number of computations are being carried out on continuous data, then the average time per computation is only 5 msec as a full computation of the coefficients does not have to be made for each point separately.

The accurate determination of radio source positions is one of the principal uses of high resolution instruments such as the Molonglo Radio Telescope. A critical stage in this process familiar to all radio astronomers involves the measurement of the instrumental response pattern relative to some accurate time or position marker. Ideally, the analysis procedure should introduce no further errors either random or systematic beyond those which are already present in the data. This is virtually impossible with chart analysis.