Lynette M. Newton

Neutral Hydrogen in the Galactic Halo

Observations of 21 cm HI emission-line profiles have been made in 34 directions from l = 172° through 0° to l =97° at high galactic latitudes and in 59 directions towards the LMC (b~ –33°) with the aim of detecting low-intensity halo features which may be compared with other element features of similar radial velocities detected by ultraviolet or optical absorption lines. Data are presented as spectra and tables of the parameters: radial velocities, line temperatures, halfwidths and column densities. Spectra of both low-intensity (halo) and high-intensity components are given for 48 positions in three tracks across the LMC. Features near radial velocities –48 and +58 km s -1 are found in all the directions examined, whereas significant numbers of features grouped around average radial velocities + 112, +160 and +373 km s -1 (Isr) are found only in the directions of the LMC. Using the HI column densities as references, we have estimated depletions in the abundances of calcium and sodium in the halo, spiral arms and the LMC disk. In one direction towards the LMC depletions in the halo features of carbon, nitrogen, oxygen, magnesium, aluminium, silicon and iron (from International Ultraviolet Explorer (IUE) satellite data) have also been estimated.

Pulsar Timing Observations at Tidbinbilla

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.

Detection of the J = 1->0 Transition of Cyanodiacetylene in Sgr B2

In November 1975 workers at the Herzberg Institute for Astrophysics in Canada (Avery et al. 1976) discovered cyanodiacetylene in Sgr B2. This molecule is the heaviest yet detected in interstellar space, having a molecular weight of 75 amu, and is the longest linear molecule known.