Australia Telescope Compact Array report
Staff
Early in February the Officer-in-Charge Dave McConnell commenced a period of being based at ATNF headquarters in Epping, and now returns to Narrabri for a week every month. The Deputy OIC, Ron Beresford, has been acting for him in the day-to-day management of the Observatory during his absence. Dave retains responsibility and involvement in the scheduling of time on the Compact Array, so all questions regarding telescope usage should still be directed to him. In any case, the OIC and deputy are in daily contact and either can assist with any kind of enquiry from users.
In September 2000 mechanical engineer Clive Murphy was appointed to the observatory staff as the Head of the Engineering Services Group. Clive comes with a wide range of experience in various industrial environments in Australia and overseas, most recently with the large Cargill seed oil plant in Narrabri.
As part of the collaboration between the ATNF and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), Taiwanese student Cheng-Jiun Ma from Taiwan is visiting the observatory for three months to gain experience in practical radio astronomy. He has been working under the experienced eyes of Ravi Subrahmanyan and Bob Sault. Cheng-Jiun investigated anomalous refraction effects at 3 mm, evaluated the antenna tracking stability using an optical telescope mounted on an ATCA antenna, and worked on data acquired in a short baseline interferometer with the aim of evaluating methods for rejecting cross-talk. He also gained experience making synthesis images of radio galaxies using ATCA data and the Miriad data reduction package.
Over the summer months the observatory hosted vacation scholars Elizabeth Claridge from the University of Tasmania and Tim Connors from the University of Sydney. Elizabeth worked with Steven Tingay on bent jets in extragalactic radio sources. Tim studied the radio emission from the globular cluster 47 Tucanae with Dave McConnell.
Visit by the new CEO of CSIRO
On 11April the new Chief Executive Officer of CSIRO Dr Geoff Garrett made a brief visit to the Observatory. In a day which started with a visit to CSIRO's cotton research station at Myall Vale (Division of Plant Industry), Dr Garrett spent several hours addressing staff and inspecting the Compact Array.
Ron Beresford, Deputy OIC Narrabri, with CSIRO Chief Executive Officer Dr Geoff Garrett and Dr Jim Peacock, Head of CSIRO Plant Industry, while at Narrabri during the recent visit.
MNRF Compact Array upgrade
The first term of 2001 has been quiet in terms of MNRF installation work, after the major receiver installation period in November and December 2000. The main progress has been towards completion of services to the new antenna station posts, both electrical power and fibre optic cables. Another major shutdown has been scheduled for two weeks beginning on 18 June 2001. During that period upgraded versions of the two 12/3-mm receivers will be reinstalled in antennas 3 and 4, and a third receiver will be mounted in antenna 2. Other important work on the new local oscillator (LO) system and the new Antenna Control Computer software is also scheduled for that period.
Ravi Subrahmanyan has been formally appointed coordinator of mm-receiver/LO system tests and commissioning and has been working closely with Bob Sault, Michael Kesteven, David Rayner and others. Commissioning and testing of the new receiver systems on antennas 3 and 4 has continued since December with significant progress in understanding a number of areas:
1) Local Oscillator and interferometer phase stability - A major improvement (factor of two) in the interferometer efficiency was achieved after recognition of a feature of the LO phase monitoring system which was causing a frequent and large variation in LO phase. Once the new LO system is installed this feature will not degrade the performance;
2) Atmosphere and its influence on performance - Large fluctuations in both single dish power and in interferometer amplitude have been identified with "anomalous refraction", the effective wandering of the antenna primary beam caused by phase gradients across the 22-m aperture. The characteristics of this effect and its variation with conditions, time of day, etc, are being investigated;
3) Pointing - An imbalance in the encoder electronics has been identified as the source of a periodic pointing error with amplitude of about 5 arcseconds. As a trial, the offending circuitry in one antenna has been aligned and the pointing error has improved markedly;
4) Optics - The antenna optics alignment and its variations with antenna elevation are being evaluated in order to improve the antenna gain and flatten the gain elevation dependence.
Initial measurements have been made of the antenna 3 subreflector translation and rotation under elevation changes. Difficulties have been encountered in isolating subreflector and quadrapod movement. Work will continue, with the aim of characterising the quite small movements that may impact on the performance of the antenna at 3 mm.
ATOMS/ACC
This project now has a good workforce with Scott Cunningham and David Brodrick working under Mark Wieringa's leadership, and Dave McConnell working remotely from Sydney. The group now reports the assembly of the first of the new Antenna Control Computers in its final form and its successful testing with a major subset of the new software.
Other observatory work
A network connection is being installed to the Lodge. This will provide more facilities for monitoring the telescope operation while relaxing over a meal. It will also serve electronic displays needed for the coming ATNF Synthesis Workshop to be held at the Observatory in September.
Visitors will admire the new staircase in the control building. This has been lengthened and tiled and provides a more gentle climb up to the observation areas. A number of improvements have been made to the grounds, including a very smart new fence around the new car park in the Visitors Centre. Being planned at present is an avenue of native shrubs along the path to the Lodge.
Dave McConnell
Officer-in-Charge
(dmcconne@atnf.csiro.au)