We present here preliminary results of further radio and optical work being carried out on the Molonglo Deep Survey (Robertson 1977a, b, c) which reaches a density of ∼ 20,000 sources per sterad at a limiting flux density of 84 mJy at 408 MHz in three small areas of sky at declinations -20° and -62°. The position errors range from 4 to 15 arc sec r.m.s. depending on flux density. Optical identifications are being made by G. W. using the Palomar Sky Survey in the -20° region and the ESO and SRC surveys in the -62° region. In the latter case, where only one colour is available more accurate positions are necessary to identify QSO candidates. The Fleurs synthesis telescope is being used to obtain accurate positions.

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: MH ∝ 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.

NGC 4945 is a ninth-magnitude southern galaxy orientated almost edge-on to the line-of-sight. De Vaucouleurs and de Vaucouleurs (1964) list its classification as SB(s)cd and its optical dimensions as 17’ x 3’ arc. It is of particular interest because 18 cm OH and 6 cm H2CO absorption has been detected (Whiteoak and Gardner 1973; Gardner and Whiteoak 1974) in molecular clouds in this galaxy which overlie the small-diameter radio source located near the nucleus. In reporting the detection of the OH absorption we suggested that the HI profile in the direction of the nucleus was affected by HI absorption. In this paper we describe a study of the HI distribution which substantiates this conclusion.

The eighth magnitude star HD 101065 is an extremely peculiar star with a unique spectrum characterized by numerous strong lines of the rare earths and the absence, or at least a remarkable weakening, of the lines of the iron group (Cowley et al. 1977). Besides the lanthanides only yttrium, zirconium, calcium and barium are definitely present in the atmosphere in substantial quantities. The evidence for the presence of lithium and strontium is subject to some doubt since these elements are represented only by one or two reasonably strong lines, which is insufficient for a positive identification in a spectrum as complex as that of HD 101065. The evidence for the presence of other elements is the subject of a critical examination in a recent paper by Cowley et al. (1977). The effective temperature of the star is about 6100 K (Przybylski, 1977) which is substantially lower than the temperature of any known Ap star. However, the effective temperature of HD 101065 is still subject to controversy (Wegner, 1976).

The Circinus galaxy (CG) was discovered on a plate of an atlas of the nebulae of the southern Milky Way (Lyngå and and Hansson 1972). The detailed optical properties of this galaxy have been investigated by Freeman, Karlsson, Lyngå and Burrell and will be published in a paper by Freeman et al. (1976). The coordinates of the optical nucleus are (1950).

The metal content of stars (and galaxies) is of great interest as it relates to the theories of element formation, and through these to the history of our galaxy, the frequency of supernovae, the star formation rate and even the quasar rate. The kinematics and metallicity of stars have been correlated in a theory of formation of the galaxy by Eggen et al. (1962). Alternate theories (Unsold 1969) have also been proposed. Much work has gone into isolating individual metal deficient stars and determining their abundances, and also the abundances for stars in clusters.

Owing to the comparative lack of radio recombination line observations of southern HII regions, it has not been so far possible to make an overall interpretation of the data for these sources. However, observations of the H90α and H252α transitions by McGee et al. (1975) and Batty (1974) respectively have usefully extended the frequency range of observations to cover ∼ 0.4 to 8.9 GHz for a few southern HII regions.

IRC + 10216, a bright infrared late type carbon star, is observed to have millimetre range line emission of the species 12CO, 13CO, CS, C2H, HC3N, CN, HCN, SiS and SiO in an extended envelope around the central infrared sources. The infrared emission arises from two concentric dust shells around the star: an inner 0”.2 arc radius shell of 600 K and optically thick, i.e. radiating as 600 K black body, and an outer shell 1″.0 arc radius at 375 K and optically thin for λ ≳ 2μ. A model explaining the line emission in terms of infrared pumping between the two lowest vibrational levels, first proposed by Morris (1975a) for IRC + 10216, was used to calculate antenna temperatures for various rotational transitions of HC3N; since there is a prima facie agreement between the calculated and observed values for HC3N we have attempted the same calculation for DC3N.

Many cold molecular clouds have been detected as a result of their association with dense optical obscuration. The HII region RCW 36 is contained within a prominent dust lane extending several degrees along a line of almost constant right ascension (see e.g. Rodgers et al. 1960). By means of H2CO and OH observations we have found that this lane is associated with a dense elongated molecular cloud.

The β Cephei variables are a group of short period pulsating variables of early spectral type for which no satisfactory physical driving mechanism has yet been discovered. Further it is not clear what form of pulsation these stars are undergoing. The existence of a beat phenomenon and a phase of spectral line broadening is well established in some of these stars. This extends to observed spectral line doubling in three stars, BW Vul, σ Sco and 12 Lac. Because of the difficulty in explaining these phenomena with purely radial oscillations, Ledoux (1951) first suggested the possibility of non-radial oscillations. Other stars in the group, γ Peg, δ Cet, #x03BE;’ CMa and β Cep have approximately sinusoidal velocity and light curves with little indication of spectral line broadening. For these there is probably no a priori observational need to look beyond purely radial oscillations. It is of course conceivable that different modes of oscillation are present in different members of the β Cephei group. However, if line profiles are calculated for various proposed oscillation modes and compared with the observations, it may be possible to eliminate some suggestions and hence limit the search for an instability mechanism.

Symbiotic stars are at the same time perplexing and rewarding to study. Their spectra contain great numbers of emission lines due to atoms in a range of ionization states from neutral to coronal. The continua are weak and usually unobtrusive: the strongest lines may have equivalent widths of thousands of Angstroms. But the crowding of weak lines complicates their measurement and, often, their identification. Many symbiotic stars probably emit weak lines which currently defy identification, but which cannot be distinguished from their neighbours. It is, however, rather rare to find a strong unidentified emission line.

Although it is well known that HII regions are present in the innermost regions of the Galaxy their kinematics are still not fully understood. In one study Pauls et al. (1976) surveyed with a beamwidth of 3′ arc the 10 GHz recombination line emission in directions within 15′ arc of the nuclear radio source Sgr A. They found that the emission velocities varied from position to position within the range -50 to + 50 km s-1but appeared to lack any overall pattern. In contrast, we have recently observed the recombination line emission from the galactic centre region with a beamwidth of 4′.5 arc, and find strong evidence of ordered motions near the galactic nucleus.

Ammonia was the first interstellar molecule with more than two atoms to be discovered (Cheung et al. 1968). Since that time it has been observed in many HII regions and dark clouds (Mayer et al. 1973; Morris et al. 1973; Cheung et al. 1973; Kaifu et al. 1975). The molecule has a rich rotation-inversion spectrum with about 10 transitions in the range 23-25 GHz. Each line has hyperfine structure which permits, in principle, the determination of optical depths, filling factors and excitation. Unfortunately line brightness temperatures are low (<1 K) so that a low-noise receiving system and long integration times are required to exploit these possibilities.

Surveys of the Galaxy at five frequencies in the range 2 to 20 MHz have been made using the Llanherne low frequency array (Ellis, 1972). The data has been assembled into maps covering the area 320° < £ < 30° and -25° < b < 22° and these are presented in rectangular galactic co-ordinates. Galactic radio spectra in various directions have been obtained, combining the new data with seven earlier galactic continuum surveys. The details of all the surveys used are given in Table I. A new 4.7 MHz map has been plotted from the profiles presented by Ellis and Hamilton (1966).

Soft X-ray photographs of the Sun taken from the manned Skylab satellite (Vaiana et al. 1973) gave, not the earliest, but perhaps the most graphic evidence that the solar corona is patchy. During the Skylab mission (May 1973 to February 1974), the solar corona as usually envisaged covered only 80% of the Sun (Bohlin 1977). The areas lacking a ‘dense’ corona are called coronal holes (Withbroe al. 1971; Waldmeier 1975).

Pulse arrival time measurements allow the determination of accurate pulsar periods, period derivatives and, provided the data span is at least one year, precise pulsar positions. If observations are frequent and reasonably regular, irregularities in the period can also be investigated. To minimize the effect of possible variations in dispersion measure, it is important that these observations be made at a relatively high frequency, preferably above 1 GHz. To eliminate pulse shape variations due to variable ionospheric Faraday rotation, the pulse total intensity or one of the circular polarizations must be recorded.