ATNF Science Highlights 2005
Multibeam pulsar surveys at Parkes
Pulsar surveys using the 13-beam multibeam receiver at Parkes
have been extraordinarily successful. Since the receiver was
installed in 1997, surveys using it have discovered about 850
pulsars, or more than half of the total now known. The system
operates at a centre frequency of 1375 MHz with a bandwidth of
nearly 300 MHz. The 26 signals (two polarisations from each
beam) are fed to a large filterbank system and the detected
signals are recorded on tape for later analysis. Several surveys
have been undertaken with the system: the Parkes multibeam
pulsar survey (PMPS), a large international collaboration which
surveyed a 10° strip along the Galactic plane, two surveys at
Galactic higher latitudes managed by Swinburne University, a
high-latitude survey by the PMPS team and a survey of the
Magellanic Clouds. The PMPS alone has discovered more than 750
pulsars making it by far the most successful pulsar survey
ever. The high-latitude surveys were optimised for discovery of
millisecond pulsars and discovered more than 20 of this
important class of pulsars, including the now famous double
pulsar. Several new classes of pulsar were discovered by the
PMPS, including highly magnetised, young but long-period
pulsars, and RRATs, rotating radio transients which appear to
just emit occasional single pulses. The double pulsar is a
fascinating system with a highly relativistic orbit enabling
unprecedented tests of gravitational theories as well as
providing unique insight into the magnetospheric physics of
pulsars.read
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Discovery of a planetary nebula around the OH/IR star V1018 Sco
The Compact Array has been used to observe a unique, recently
formed planetary nebula that is associated with a long-period
OH/IR variable star, V1018 Sco. This star is still in the
asymptotic giant branch stage of evolution and the OH maser
emission varies periodically as the central star pulsates over a
cycle of 1500 days. The star has a strong stellar wind and an
extremely large OH shell. Radio continuum observations taken
with the Conmpact Array show two regions of continuum
emission. Both are nonthermal, with radio spectral indices
comparable to those seen in colliding-wind Wolf-Rayet
binaries. For V1018 Sco the nonthermal radio emission also
indicates a wind-wind collision, but in this case the collision
is between a cool slow wind and a hotter faster wind that has
recently turned on from the same star. read more |  |
Shining a bright light on cold gas in the Magellanic Clouds
Our nearby neighbour galaxies, the Large (LMC) and Small
Magellanic Clouds (SMC) are ideal laboratories to probe the
state of the different gas phases in galaxies. Stars are born
from dense and cold gas, mainly in molecular form. In turn,
young massive, newly born stars dump enormous amounts of energy
back into their natal gas clouds, changing its parameters in the
process. This drastically disturbs the ability of molecular gas
clouds to further form stars. In the LMC, 30 Doradus is such a
very prominent region of star formation and energy feedback. A
long string of molecular clouds is stretching away from 30
Doradus, which are ideal circumstances to probe the state of the
molecular gas in regions with high flux of ionising, ultraviolet
(UV) photons from young stars and much quieter environments. As
a large survey, we observed the abundant carbon monoxide (CO)
molecule with the AT Mopra telescope over this very extended
region. We find that the sizes of molecular clouds are strongly
influenced by the UV photons and that CO tends to be destroyed
more readily than the more abundant hydrogen molecule
(H2). This has implications on estimates of the
molecular gas content and hence the potential to form stars in
galaxies observed in the very far and early Universe. read more |  |
Pinpointing Huygens: VLBI observations of the probe s descent
On 14 January 2005 the European Space Agency (ESA) Huygens
probe descended on to the surface of Saturn's moon, Titan. During the
descent and for the three hours that the probe continued transmitting
after it landed on the surface, the ATNF radio telescopes - Parkes,
the Compact Array and Mopra, along with the University of Tasmania's
telescopes in Hobart and Ceduna and 12 other telescopes in the USA,
China and Japan were used to track the trajectory of the descent using
the technique of Very Long Baseline Interferometry (VLBI). The
position of the probe can be determined to an accuracy better than
1~km every minute - from a distance of over 1 million km.
read more |
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Supersonic jets from massive stars
Now equipped with new 12- and 3-mm receivers, the Australia
Telescope Compact Array can measure the flux of an astronomical
source over discrete wavebands spanning the frequency range 1 to
100 GHz. In an ongoing project, Brooks and her collaborators are
using this valuable capability of the Compact Array to study one
of the most massive young stellar objects known to harbour a
supersonic jet of ionised gas. The jet is associated with the
infrared source IRAS 16547-4247, located at a distance of 2.9
kpc and which has a bolometric luminosity that is equivalent to
that of a single O8 zero-age-main-sequence star. This is the
first reported case of a radio jet associated with a young
O-type star, supporting the notion that the accretion mechanism
that produces jets in low-mass star formation also operates in
the higher-mass regime.
read more |
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Compact Array images dense gas in a circumnuclear ring
The ATCA, with its 3 mm receivers and hybrid array
configurations, has opened up new avenues to investigate the
nature of molecular gas at the centres of galaxies with high
angular resolution and sensitivity. HCN and HCO+ are
two molecules tracing high density gas (above 104
particles per cubic centimetre), with emission lines at 88.3 and
88.9 GHz. We have used both transitions to image the
distribution of dense
molecular gas in the central regions of NGC 1433 and NGC
7552. The distribution of the gas can be compared with that of
the massive stellar population as derived from HST UV
imagery. Such a comparison enables us to determine the
conditions of molecular gas in areas of massive star formation.
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