They're here
Figure 1: Peter Mirtschin (ATNF Narrabri) admires the newly installed 3-mm system.
Five antennas of the Compact Array are now outfitted with 3-mm systems operating at 85 – 105 GHz. First fringes were obtained at 7:10 pm on 20 September. They marked the culmination of the Compact Array's high-frequency upgrade, largely funded by the first round of the Commonwealth government's Major National Research Facilities program. Previous newsletters have featured developments in the saga. As those who've been following them will know, the upgrade has involved change on many fronts:
* construction of six new receiver packages incorporating the broadband 3- and 12-mm systems (and provision for a future 7-mm system);
* a new fibre-based reference distribution system for the local oscillators;
* the design of LO multiplier chains for the 3- and 12-mm receivers;
* new ATNF-designed helium scroll compressors;
* new antenna panels, and re-adjustment of the antenna surfaces;
* construction of an atmospheric seeing monitor;
* new antenna control computers; and
* the building of the north-spur and additional stations.
Not to mention blood, sweat, toil and tears.
The promise of the 3-mm system attracted 50% more Compact Array proposals than usual for the 2004 MAY term. Less than four hours after the first fringes hit the screen, the first scheduled observations began. Fifteen projects involving 3-mm observations were carried out between 20 September and mid-October, when the observing season ended. Elaine Sadler (University of Sydney) was a member of the team for one of the earliest projects — an ambitious attempt to detect CO at a redshift of five. "I was just amazed at how well [the system] worked," she said. Having the capacity to observe at both 12-mm and 3-mm wavelengths is extremely useful, Sadler said. "For galaxies at a redshift of four, you can observe the CO (1-0) transition at 12 mm and the (5-4) transition in the 3-mm band. These complementary tools give you a more complete picture of the physical condition of the gas at the time these galaxies are having their first big burst of star formation." James Urquhart (University of Leeds) had two projects on the go. "As a new user of the 3-mm system I was a given a lot of support from all of the staff I came in contact with, especially Bob Sault and Juergen Ott," he said. "The telescope performed extremely well during my shifts; I didn't experience any significant problems." For the first science results from the 3-mm system, see Simon Ellingson's article in this newsletter.
The first two 3-mm systems for evaluation were fitted to the Compact Array in 2000, seeing first light on 30 November. From there to the installation of the final systems has been a long slog for many ATNF staff. "But first of all the credit goes to the engineers and technicians who designed and built the 3-mm system," said ATNF's Baerbel Koribalski, who chaired the science team of the 3-mm project for some time. "The difficulties of achieving such an innovative system were simply underestimated, but [they were] ultimately overcome, and that's what counts." High standards were set for the fabrication of components, and they were met and exceeded by both ATNF workshop staff and external service providers, such as machinists, electroplaters and manufacturers of printed circuit boards.
The key components of the new receivers are indium phosphide (InP) low-noise amplifiers (LNAs) and frequency conversion mixer MMIC chips, designed by CSIRO engineers and fabricated by Velocium, a business unit of telecommunications giant TRW (now Northrop Grumman). "One of our first issues was how to make LNAs that would give the broadband coverage we needed," said Warwick Wilson, Head of Engineering. "SIS receivers couldn't do it." And so, through connections that John Archer (CSIRO ICT Centre) had made with the US telecommunications giant TRW, the ATNF started an ambitious program of designing its own special-purpose indium phosphide devices. Koribalski recalls a visit from Steve Giugni, now Deputy Director of CSIRO's ICT Centre, probably in late 1994: "He jumped into my office and said something like, Can you find a few hundred thousand dollars? There's an opportunity to make some chips with TRW." In the end, the funding to develop millimetre-wave integrated circuits for radio astronomy and telecommunications came from a special program established by former CSIRO Chief Executive Malcolm McIntosh. The 3-mm receivers currently installed are operating at up to 105 GHz, the frequency limit imposed by the InP circuit designs; more recent designs will allow higher frequencies to be reached in future, Wilson said.
The Compact Array will now be one of the world's most sensitive millimetre arrays. Until the advent of ALMA, it will be the only Southern Hemisphere array working at short wavelengths. "The Compact Array will provide a baseline knowledge of southern millimetre sources that until now has been sorely lacking," said Tony Wong, ATNF project scientist for the 3-mm system. "This has already generated substantial interest from the prospective ALMA user community, including several groups here in Australia. The array has some intrinsic constraints — lack of short baselines, a small field of view, and a less than perfect site – but we are working to make it perform as well as possible at millimetre wavelengths," he said.
Astronomers worldwide are invited to apply for 3-mm observations next winter (May – October). Applications are due by 1 December 2004.
Helen Sim
(Helen.Sim@csiro.au)