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Our current understanding of Herbig-Haro objects and their relationship with outflows and Pre-Main-Sequence objects is limited. Although the general mechanism of outflows is understood, the detailed questions concerning the outflowing material’s origin and the collimation mechanisms remain largely unanswered. The role of multi-waveband observations (visible, infrared and radio) is vital to our understanding of the shock dynamics of outflows.This paper discusses high spatial resolution near infrared maps of three outflow complexes, HH34, HH46/HH47 and HH54, made using the Anglo Australian Observatory’s infrared camera, IRIS. For the first time molecular hydrogen emission is observed associated with the edges of outflow cavities. In the cases of HH46/47 and to a lesser extent HH34 molecular emission is seen coincident with highly collimated jets feeding the outflow cavities.

The effects of including low quality IRAS flux data in colour-colour diagrams is investigated, with a view to identifying Young Stellar Objects from the IRAS database. Colour criteria to perform this task are derived.

During 1990 we surveyed the southern sky using a multi-beam receiver at frequencies of 4850 and 843 MHz. The half-power beamwidths were 4 and 25 arcmin respectively. The finished surveys cover the declination range between +10 and −90 degrees declination, essentially complete in right ascension, an area of 7.30 steradians. Preliminary analysis of the 4850 MHz data indicates that we will achieve a five sigma flux density limit of about 30 mJy. We estimate that we will find between 80 000 and 90 000 new sources above this limit. This is a revised version of the paper presented at the Regional Meeting by the first four authors; the surveys now have been completed.

through the whole cloud, but is predominantly located close to the near-face of the cloud. Dust excess determinations show that the Trapezium Cluster stars sampled here contain a typical proportion of classical (dust-excess) T Tauri stars compared with naked (no dust-excess) T Tauri stars for a young stellar population. Approximately one-third of our sample have insignificant dust excesses.Calcium IIIR triplet emission is observed in members of our Trapezium Cluster sample. We judge that the strengths of the triplet features imply a circumstellar disk origin for the emission. The frequency of calcium triplet emitting stars is estimated for our sample. We compare this estimate with the proportion of triplet emitters in a sample of Chamaeleon pre-main sequence stars. We find that 20-30% of classical T Tauri stars in the two populations exhibit triplet emission; the frequency of triplet emission in the Trapezium Cluster sample is found to be comparable with that in Chamaeleon.We perform an approximate dynamical analysis of the Trapezium Cluster star-forming region using our estimates for stellar mass and age. The low mass cluster is found to be at an early stage in its dynamical evolution, and has not had time to completely relax as a system and lose its initial characteristics. It is too young, therefore, to exhibit mass segregation, and the observed isothermality of the stars is proposed here to arise from the distribution of the clumps from which the stars have formed. The high mass stars considered separately are determined to be old enough to have relaxed as a system. We find that, if the 0 1 Ori stars are located centrally with respect to the low mass cluster, then they are most likely to have formed in their present locations rather than have arrived there from larger radii through dynamical friction processes. In addition, the binding energies of the two high mass binary systems are found to be almost forty times the energy of the low mass cluster. It is suggested that the binary energies must have been acquired through their formation processes instead of through dynamical interations with the low mass cluster. Thus, present characteristics of the stellar population of the Trapezium Cluster directly relate to the conditions under which the cluster formed, and are not due to dynamical processes among the stars themselves. The total stellar mass determined for the low mass cluster is estimated to be sufficient to bind the cluster at this time. This remains true even with future removal of gas from the region. However, continued dynamical intereactions may lead to the eventual dissipation of the low mass cluster. A STUDY OF SOME NUCLEAR REACTIONS RELEVANT TO OXYGEN BURNING IN SUPERNOVAE Alistair F. ScottPhysics Department, University of Melbourne, Parkville Vic 3052 February 1993 This thesis describes the measurement of absolute cross section and calculations of thermonuclear reactions rates for a number of reactions of importance to explosive and carbon burning.The results of calculations made with the s...