Australia Telescope Compact Array report
Highlights
The winter season has seen a number of milestones reached, with first astronomical use of the north spur, the new antenna control computers and a wideband correlator.
The north spur was christened on 12 August 2002 with the H75 configuration - an ultra compact configuration where the maximum spacing is about 100 metres. This array, which gives high brightness sensitivity imaging and a full synthesis in about 6 hours, was also popular with 3-mm observers (Figure 1). We have since revisited it with H168.
Figure 1: The first image formed using the H75 array: Radio galaxy J0116-473 at 3 cm, observed using a 9-pointing mosaic. The Fourier plane was essentially filled in six hours.
The christening of the north spur coincided with a visit by Michael Murphy and Steve Curran and an accompanying ABC Catalyst filming crew. Michael and Steve are involved with the work suggesting that the speed of light has changed with time. With them doing related ATCA observations, the film crew used the array as a photo opportunity for their story.
The new antenna control computers were first rolled out for astronomical use in mid-July, and then again in early/mid-September. Although there were problems in the July runs, which caused some gnashing of teeth, the September runs were far more successful (Figure 2). All antennas are now outfitted with the new antenna control computers and it is a routine process to switch between the old and new systems. Completing the project and making the new antenna control computers the standard observing system is now well within our sights.
Figure 2: One of the first images produced using data observed with the new antenna control computers. An HI column density image of the edge-on spiral E115-G21. Courtesy of Jess O'Brien.
Driving the new antenna control computers towards completion was the need to support a single baseline wideband continuum correlator (3.5 GHz) developed by Warwick Wilson and his group. This correlator, together with the new antenna control computer, has allowed a pilot of large-area 12-mm blind survey to be performed. During this survey, as an after lunch diversion, Warwick Wilson and Mike Kesteven realised that the two correlators (the normal ATCA and the wideband correlator) could be run in parallel. They then implemented a split-array mode within a few hours.
On top of these achievements, we cannot forget that this winter was the first one where three of the preliminary 12- and 3-mm systems have been offered. 22% of observing time over the winter was at 12- and 3-mm wavelengths. In some configurations, the antennas were "shuffled" out of the natural order. This allowed the Fourier coverage of the millimetre systems to be optimised. To a significant extent, this winter has been a trial run: it has allowed us to develop a better understanding of the millimetre systems, to start working on some of their problems, and to help start to build up expertise in millimetre interferometry within the ATNF community. Additionally it was an experiment in scheduling: to give some robustness against poor weather, a mode of flexible scheduling was used. In this mode, a millimetre project can swap with a partnering centimetre project. With a pronounced drought, the weather (as seen by an astronomer) has been very good over the winter, with only about one swap in nine being initiated. In total, we have registered only three hours of "lost millimetre time" because of weather. These three hours was reclaimed by a centimetre NAPA project.
Well done to all ATNF staff and observers for their contributions to these milestones!
Staff and visitors
In August, we farewelled Darryl Campbell, who has left us after 13 years to take on a position with the National Parks service in the Narrabri area. We wish Darryl all the best.
Allan Day is going to escape the heat of a Narrabri summer in a serious way: starting in late October, Allan is taking leave-without-pay for 16 months to work at the South Pole on the DASI experiment.
On the positive side of the ledger, we welcome Mike Hill, Scott Munting and Brett Hiscock. All three have recently joined our electronics group. Mike joins us from South Africa, Scott from CSIRO Marine Research in Hobart and Brett from Sydney. Additionally, we will be welcoming Michael Dahlem early in the new year. Michael joins us from ESO in Chile, and will work in a systems role.
Lakshmi Saripalli has taken on a role as the editor of this newsletter, preparing for when Steven Tingay leaves us at the end of the year.
Currently we are advertising for a SKA postdoctoral position as well as an operations-scientist/engineer with duties mainly associated with Mopra.
We have had a number of medium-term visitors at the ATCA recently: Gianni Bernardi, James Urquhart, Jared Cole and Kate Smith have all stayed several weeks to a couple of months, working on observing or engineering projects.
Operations
Figure 3 gives the usage of the Compact Array for the 2002 May term.
Figure 3: Compact Array usage for the 2002 May term
Astronomy usage this term is down by 5.0% compared to January term, with all categories of non-astronomical use increasing slightly. This is a reflection on the larger number of array configurations scheduled this term, that two array configurations (EW214 and H75) were used for the first time, and that there was extra maintenance associated with these and the wideband correlator. Lost time was up slightly, mainly as a result of two events: a complete power failure in the Control Building and problems associated with using the new antenna control computers. These two events together cost us 16 hours in lost time.
The pay TV interference that has affected 13-cm observers for the last few years has gone. This, apparently, was a commercial decision on the part of the pay TV operator. As a result, the recommended 13-cm frequency has now changed to 2368 MHz. This is now a good, RFI-free frequency.
Site safety
As part of an effort to improve our safety act, visitors to the ATCA now need to undergo a brief safety induction. There are two levels of induction for visitors - one that caters for visitors who use the Lodge and Control Building only, and a second level that caters for those who may also need to visit the antennas outside work hours (e.g. millimetre observers and duty astronomers). As this second level can only be done when the antennas are idle, please check the observing schedule and plan ahead if you want the antenna induction.
Mopra
Mopra has been almost continuously scheduled from late June to mid-November. The time has been split between "national facility" 3-mm observing time, 3-mm time available to UNSW observers, and about three weeks of VLBI/VSOP time. During most of the "national facility" time, the ATNF has provided a telescope assistant to help support the observers. Although Mopra remains a more difficult observing environment than the other ATNF telescopes, this winter has proceeded reasonably well. Apart from one cryogenics problem (which resulted from a false fire alarm), there have been no major failures.
A late breaking development is that, as part of an ARC proposal with UNSW, Sydney University and the Monash, we have recently won funding to upgrade the Mopra correlator to 8-GHz bandwidth. This bandwidth would be used in conjunction with the new 3-mm front-ends. Given this, and with the current season almost behind us, we are reviewing how best to support the telescope's operation in winter 2003.
Bob Sault
Officer-in-Charge, Narrabri
(Bob.Sault@csiro.au)