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| The Australia Telescope Compact Array at
Narrabri, NSW. |
Dr Tong Wong and A/Prof Michael Burton in
the Department of Astrophysics, UNSW. |
As far as astronomy is concerned, the radio part of the spectrum encompasses
all wavelengths of light greater than about 0.5 mm. Wavelengths greater
than 1 cm have long been studied by radio observatories around the
world, but the shorter millimetre and sub-millimetre wavelengths have
been relatively less explored, partly because of the difficulty of
building sensitive receivers in this range and partly because of the
obscuring effects of the Earth’s atmosphere. However, radiation
at these wavelengths carries crucial information about the cold dust
and molecular gas from which new stars are born. These wavelengths
are also well-suited for observing old stars, solar system bodies,
and the leftover radiation from the Big Bang, among other things.
In order to observe astronomical sources in this wavelength range
at high angular resolution, a number of millimetre arrays have been
constructed around the world, two in the United States (soon to
be combined into a single large array in California), one in France,
and one in Japan. Meanwhile a Sub-Millimetre Array (SMA) is under
construction in Hawaii. However, the southern hemisphere has lacked
a millimetre array until now: the CSIRO’s Australia Telescope
Compact Array (ATCA), previously operating only at wavelengths greater
than 3 cm, is being equipped with state-of-the-art 3-mm and 12-mm
receiver packages. When this upgrade is complete in mid-2004, the
ATCA will be a superb instrument for studying star formation in
the Milky Way and its satellite galaxies (the Magellanic Clouds),
all of which are best viewed from the southern hemisphere.
In the meantime, a prototype 3-mm system has been available on
three antennas of the ATCA since late 2001 and has been extensively
used by astronomers at UNSW’s School of Physics. Our research
programmes include observations of molecular gas in nearby starburst
galaxies, searches for biologically important molecules, and studies
of regions in our Galaxy where massive star formation is known to
be occurring based on surveys of ionised gas and methanol masers
conducted at centimetre wavelengths. Because of the limited tuning
range and imaging capability of the prototype system, these observations
have been used mainly to supplement data taken from single-dish
facilities, in particular, the Mopra Telescope and the Swedish-ESO
Submillimetre Telescope (SEST). However, once the upgrade is complete,
the high angular resolution, superior imaging performance, and exceptional
gain stability provided by the ATCA will make it the instrument
of choice for a variety of studies. UNSW’s depth of experience
in millimetre astronomy, a result of its collaboration with CSIRO
in the operation of Mopra, will place it in a prime position to
exploit the ATCA’s new capabilities. Meanwhile, the Mopra
Telescope, itself the subject of a major upgrade, will soon be able
to efficiently scan the sky to identify sources for high-resolution
ATCA follow-up.
Tony Wong
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