Infrared Astronomy: in the Heat of the Night
The 1999 Ellery Lecture
J.W.V. Storey, PASA, 17 (3), 270.
Next Section: CONCLUDING REMARKS
Title/Abstract Page: Infrared Astronomy: in the
Previous Section: TWENTY-FIVE YEARS OF AUSTRALIAN
Contents Page: Volume 17, Number 3
|
Subsections
For the past quarter century the 4-metre telescope has been the ultimate tool
for ground-based astronomical research. This is no longer the case. There are
now a number of 8 and 10 metre telescopes in operation, and even more under
construction. In the infrared, where the image size can be that of the
entire diffraction-limited telescope aperture (using
adaptive optics in the near-IR, or simply taking advantage of good seeing
conditions in the mid-infrared), the point-source sensitivity goes as the
square of the telescope diameter. The advantage of a large telescope in the
infrared is thus substantially greater than it is in the visible, where
sensitivity usually improves only linearly with telescope diameter.
Furthermore, the new generation of large telescopes are being built on superb
infrared sites, and the telescopes themselves (especially Gemini) are being
optimised for extremely low emissivity in the IR. Unfortunately, all these
factors argue against the construction of a future large optical/IR telescope
in Australia. However, by becoming a 5% partner in the Gemini project,
Australia has been able to maintain access to some of the best facilities in
the world, an essential prerequisite for the continued health of the country's
astronomy program.
Australia has also been able to capitalise on its strengths in infrared
instrumentation within the Gemini partnership, recently signing a contract
for the fabrication of a near-infrared integral field spectrograph (NIFS)
for Gemini North. To be built at Mount Stromlo Observatory, NIFS is
designed to make full use of the high resolution capabilities of the
adaptive optics facility of the telescope.
In the US, two major projects are about to come to fruition. The first, SIRTF
(the Space Infra-Red Telescope Facility) is due to be launched in December
2001 (Bicay et al. 1998). SIRTF will be placed into an earth-trailing
heliocentric orbit, and will observe from 3 to 180
m. It will have
cryogenic optics, and a primary mirror diameter of 85 cm. The second major
aerospace project, SOFIA (the Stratospheric Observatory for Infrared
Astronomy), is the successor to the Kuiper Airborne Observatory. (See, for
example, Erickson & Davidson 1995; Becklin 1997.) A joint venture of NASA and
the German DLR, SOFIA will carry a 2.5 metre telescope to a flight altitude of
12.5km and will observe from 0.3m to 1.6mm. Its first science
flights are scheduled for 2001.
While two-telescope interferometry in the infrared has been a reality for the
past quarter century, the next few years will see an explosion in the growth
of this field. Both heterodyne interferometry (eg., Lipman et al. 2000) and
direct-detection methods (eg., Koresko et al. 1998; Young et al. 1998; Mennesson
et al. 1999) have now reached a high level of maturity. The very high spatial
resolutions obtainable promise the detection of circumstellar discs,
jupiter-like planets around other stars, and the opportunity to explore deep
into the cores of active galactic nuclei.
For ground-based telescopes in the thermal infrared, background radiation from
the atmosphere and the telescope remains the fundamental limit to achievable
sensitivities. By going to the Antarctic plateau, where ambient temperatures
fall to -80
C and the sky is exceptionally dry, substantial
improvements in performance can be expected. There are also strong
indications that the seeing from high altitude Antarctic sites is better
than from anywhere else on the earth's surface (Gillingham 1993b). To date all
of the infrared site-testing work in Antarctica has been carried out at the
Amundsen-Scott station at the South Pole (Ashley et al. 1996; Nguyen et al.
1996; Smith
& Harper 1998; Phillips et al. 1999; Chamberlain et al. 2000). The results
there show a 10 to 50 fold decrease in sky brightness across the infrared,
implying very large gains in the sensitivity could be achieved.
Of all the nations currently involved in astronomy, Australia stands to benefit
the most from the deployment of a medium-size infrared telescope on the
Antarctic plateau. Not only does Australia have a tradition of Antarctic
exploration, but also has a major, ongoing national Antarctic program.
Furthermore, there are no observing sites in Australia that can compare with
those in Chile or Hawaii, and Australia is actually closer to Antarctica than
it is to those sites anyway!
With these considerations in mind, Australia is currently leading the push to
deploy a medium-size (2 metre) infrared telescope on the Antarctic plateau.
Such a telescope could not only perform unique science in its own right; it
could also act as a ``finder'' telescope of unsurpassed capability for Gemini
and perhaps the NGST.
Next Section: CONCLUDING REMARKS
Title/Abstract Page: Infrared Astronomy: in the
Previous Section: TWENTY-FIVE YEARS OF AUSTRALIAN
Contents Page: Volume 17, Number 3
|
© Copyright Astronomical Society of Australia 1997