Compact Array and Mopra report
Operations
We are now in the final parts of the 3-mm observing season. While this winter has been more typical in terms of rainfall (unlike the drought of 2002), the number of "swaps" of millimetre/centimetre projects that were initiated remained low, and the fraction of good weather for the 3-mm observing was high. This year however there were a small number of 3-mm and 12-mm observing runs that were effectively ruined by poor weather. This is in contrast to 2002 when there were essentially none.
With major upgrades to the antenna receivers, local oscillator systems and control computers in April, May and June, it is very pleasing that the downtime fraction improved this term. 40% of the downtime was due to wind stow conditions (Figure 1). There were few teething problems of any significance in bringing the new systems into routine use, a major tribute to all those involved in developing and commissioning these systems.
Figure 1:Usage statistics for the May term
The new antenna control computers are now paying back the large investment put into their development. In addition to significantly improved reliability, the enhanced flexibility of monitoring aspects of the system (e.g. antenna drives) is allowing us to better tune the antennas. The new control computers are also allowing observing modes that would have been difficult or impossible with the old computers. For example, the Compact Array is currently undertaking an all-sky survey which uses a fast scanning mode made possible with the new system.
Work is proceeding on porting all the observing system to a LINUX environment, with the "first fringes" achieved with the new software on 10 September.
The flow of science using the new 12-mm systems increased significantly during the last few months, with the first polarimetric images and first mosaics being produced (see the separate article on SN1987A at 12 mm). The 12-mm system is proving to be excellent overall.
Radio frequency interference at the Compact Array
At different times over the last few months, the observatory has had a number of instances of significant radio frequency interference (RFI) affecting our HI observers. Two sources of interference were tracked to equipment outside the ATNF's direct control. However in both cases, the equipment owners acted promptly when they became aware of our difficulty. The third significant source of interference was tracked to our masers that were undergoing temporary major maintenance outside the screened room. This, too, has been resolved. Although these have been resolved, there are a number of lower-level RFI signals. Despite the greater robustness of an interferometer to RFI, we need to remain vigilant. We are currently buying some test gear to help us locate RFI in a more straightforward manner.
Staff
Ollie Dowd has recently left us. For the last 11 years, Ollie has been one of our maintenance fitters devoted to the health of the mechanical components of the antennas. Ollie leaves us to take on a position in Victoria. Le-Cuong ("Lee") Nguyen has also recently left Narrabri. Lee is a student from the University of Technology who was with us for six months as part of his industrial experience. Lee made significant steps in implementing the new telescope monitoring software, which will soon be introduced to complement the new antenna control computers. With Lee's departure, we welcome Stjepan Koljatic ("Steve"). Steve is an electronics student from Latrobe University, who is currently completing his industrial experience component of his course.
Outreach
The last few months have seen a variety of outreach efforts being undertaken. At the professional end of the spectrum, we hosted three separate tours by large groups of astronomers who were mainly in Australia to attend the IAU. In total, about 70 professional astronomers (other than our usual observers) visited the Observatory in the weeks around the General Assembly.
On 6 October we hosted a low key Open Day for the general public (Figure 2). The main attractions on offer were the Visitors Centre, an antenna vertex room and the Control Room. A total of 250 - 300 people attended, with 197 people visiting the antenna vertex rooms. The local Apex Club put on a sausage sizzle - but unfortunately drizzly weather forced the cancellation of a jumping castle.
Figure 2:A crowded Control Room during the Open Day
Part of the preparation for the Open Day included the production of a new brochure on the Compact Array, as well as a new "Welcome" poster panel for the Visitors Centre. Work in progress includes major new landscaping work around the Visitors Centre, and the repair of the "People's Telescope" (a simple solar radio telescope).
Mopra
The Mopra millimetre observing season has recently finished, with the final observations on 5 October. The 3-mm receiver system performed well over the winter, with only a few problems associated with ices in the 4-K stage of the cryogenics. Surface adjustments have considerably improved the surface accuracy of the antenna (from 260 μm to about 160 μm rms). Coupled with improvements to the "coma lobe" problem in May, the aperture efficiency of the telescope is also significantly improved. With the completion of the main observing season, a new antenna control computer has been installed at Mopra, and is in the process of integration with the observing system. Despite these positive steps, Mopra, remains a difficult observing environment. It still requires significant development to achieve its full potential as a 3-mm spectroscopic instrument. With the closure of SEST, and the concentration of APEX at shorter wavelengths, Mopra is the only telescope of its class in the southern hemisphere.
In previous years, Mopra has played a significant role in VLBI observations associated with the VSOP spacecraft. Unfortunately this spacecraft had a major failure in February. Spacecraft operation was re-established in September, but failed again only a matter of weeks later. The future of VSOP observing remains unclear.
Bob Sault
Officer-in-Charge, Narrabri
(Bob.Sault@csiro.au)