was a discussion page and was updated regularly during the
weeks before the 11 May 2001 deadline for Major National Research
Facility funding proposals.
page for a brochure describing the Douglas Mawson Telescope.
Science with the Douglas Mawson Telescope
"Science with the DMT" workshop was held at UNSW on Friday
4 May 2001 from 1-5:30pm. 28 attendees from 6 institutions
participated in a discussion of a wide range of science projects
for which the DMT would be well suited.
left to right: Peter McGregor, Jon Lawrence, Michael Pracy,
Charley Lineweaver, Warwick Couch, Peter Tuthill, Roger Haynes,
Steve Curran, Jill Rathborne, Rudold Salib, Michael Murphy,
Maria Hunt, Carl Akerlof, Paul Jones, Angie Shultz, John Webb,
Tony Travouillon, Andre Phillips, Ian Bond, John Storey, Peter
programme was as follows:
1:00 - 1:45 John Storey (UNSW) Introduction
1:45 - 2:10 Michael Ashley (UNSW) Science overview
2:10 - 2:25 Ian Bond (U. Auckland) Gravitational microlensing
2:25 - 2:40 Carl Akerlof (U. Michigan) Gamma ray bursts
2:40 - 3:05 John Webb (UNSW) Cosmology with the DMT
3:05 - 3:25 Jill Rathborne (UNSW) SPIREX/Abu results from
the South Pole
3:25 - 3:50 Afternoon tea
3:50 - 4:10 Warwick Couch (UNSW) Galaxies in the early universe
4:10 - 4:35 Peter Tuthill (U. Syd) Interferometry and astrometry
4:35 - 4:45 Peter Gillingham (AAO) Instrumental considerations
4:45 - 5:30 Discussion
During Warwick's talk
Background to the Douglas Mawson Telescope
Douglas Mawson Telescope (DMT) is a proposed 2-metre IR-optimised
telescope to be built at Concordia Station, Dome C, Antarctica.
It will be operated as a collaboration between Australia,
France, Italy and the USA.
proposal to build a 2-metre IR telescope on the Antarctic
plateau goes back many years, with a preliminary
science case developed in 1994. However, it is only recently that the site-testing
data has been available that makes the case for building such a
telescope compelling. This work was in collaboration with
the US Center
for Astrophysical Research in Antarctica (CARA).
specifications of the telescope
optimised with sub-mm capability,
arcmin unabberated field of view,
Hz SiC fast-tip-tilt secondary,
temperature -80C, survival to -100C.
interesting question is whether the telescope mounting should
be equatorial or alt-az. The alt-az advantage is cost, although
this should not be such a factor at the Dome C latitude of
-75 degrees. The disadvantage of alt-az is that you require
an instrument rotator, which complicates the hardware and
software, and leads to a rotating point-spread-function and
difficulties in precision flat-fielding.
major new research base, called Concordia
is being constructed at Dome C by the French
Antarctic programs. Concordia will open for year-round operation
in 2003, and will support a winter crew of up to 15 people.
Concordia is being built at Dome
some 1600 km from the South Pole, and 1200 km from the Australian
coastal station of Casey. Conditions
for infrared astronomy at Dome C are extraordinarily favourable.
Winter-time temperatures drop below -80C, while the wind remains
extremely low with an average speed of just 2 m/s. A more
general workshop on Astrophysics
at Dome C
will be held in Hobart on 28 - 29 June, 2001.
1994, JACARA (the Joint Australian Centre for Astrophysical
Research in Antarctica) has been actively exploring the potential
of Antarctica for astronomy. The complete
includes 21 papers in refereed journals, 30 conference papers,
19 popular articles, 11 poster papers, and 12 student theses,
as of April 2001.
DMT will have exceptional
in the thermal infrared, with a sensitivity for wide field
mapping and for observing extended objects that is comparable
to or better than 8-metre class telescopes (with their narrower
fields of view) at temperate sites.
the DMT will also be equipped with sub-millimetre instrumentation,
allowing it to build on the success of the 1.7 metre AST/RO
currently operating at South Pole.
following table, from Burton et al (Pub. ASA, in press, 2001),
shows sky backgrounds (in Jy/square arcsecond), relative signal-to-noise
ratios, and sensitivities in magnitudes (5 sigma, 1 hour)
comparing 4 telescopes in K, L and N bands for both wide-field
(per square arcsecond) and point-source (i.e., diffraction-limited)
Telescope --> Mauna Kea 8m SSO 3.9m Antarctic 2m Antarctic 8m
Wide Point Wide Point Wide Point Wide Point
Field Source Field Source Field Source Field Source
Sky background 0.003 0.003 0.00015 0.00015
Relative S/N 1.0 1.0 0.5 0.2 1.1 0.3 4.4 4.0
Sensitivity 21.5 23.1 20.5 21.3 21.2 21.0 22.8 24.1
Sky background 2 3 0.1 0.1
Relative S/N 1.0 1.0 0.4 0.2 1.1 0.3 4.5 4.5
Sensitivity 16.7 17.8 15.3 15.5 16.9 16.4 18.4 19.4
Sky background 200 1000 20 20
Relative S/N 1.0 1.0 0.2 0.1 0.8 0.2 3.2 3.2
Sensitivity 11.8 11.5 9.9 8.9 11.2 9.5 12.7 12.5
that care should be used in interpretting the above table.
In particular, the point source sensitivities assume diffraction
limited performance, which corresponds to 0.05 arcsecs at
K for an 8-m telescope. If you are not diffraction limited,
then the sensitivity will be correspondingly reduced, which
will favour the smaller telescope. Also, if adaptive optics
is used on the 8-m telescope, this will introduce a number
of additional reflections from warm mirrors, with a corresponding
increase in background.
following figure shows model calculation of the atmospheric
transmission at the South Pole across the thermal infrared,
from 2-500um, corresponding to 164um of precipitable H2O,
plus an aerosol visibility of 100km (these numbers are based
on our site-testing data from the MISM instrument at the South
Pole, see Hidas et al., PASA, 17, 260 (2000)).
windows for ground based astronomy are opened in the mid-IR
between 20 and 50um, and even windows at 200 and 220um may
optical and near-infrared (up to 2.5um) wavelengths, the DMT
will have two advantages over other telescopes.
at the site will allow exceptionally good photometry [note:
the hyperlink is to a PowerPoint presentation in French].
observation of the many circumpolar sources will enable
variability studies to be conducted that are impossible
at other locations, and facilitate microlensing and other
should be remembered that the DMT is a general purpose telescope
and in fact will be the third-largest one to which Australian
astronomers have significant access.
should stress that the MNRF proposal is not envisaging an
initial suite of instruments to make the DMT as flexible as,
say, the AAT or 2.3m. However, the size of the telescope does
make it practical for University consortia to realistically
fund and build an instrument in Australia that is internationally
Microlensing from the Antarctic - Philip Yock, U. Auckland
following is an excerpt from "Observations
from Australasia using the Gravitational Microlensing Technique",
Phillip Yock, PASA, 17, 35. Bold emphasis has been added.
realise the full potential of the gravitational microlensing
technique it is necessary to monitor millions of stars with
good photometric accuracy at a sampling rate of a few observations
per hour in several passbands. The existing network of southern
survey and follow-up telescopes (MACHO, OGLE, EROS, GMAN,
PLANET, MPS and MOA) do a relatively good job of monitoring
the Galactic bulge and the Magellanic Clouds. Further improvement
may be expected to occur soon as new image subtraction techniques
with better photometric accuracy are refined and incorporated.
quantum leap might be realised with a telescope at the Antarctic.
The idea has been raised before (Sahu K., 1998, in Astrophysics
from Antarctica, ed. G. Novak and R. Landsberg (ASP Conf.
Series) 179; and Muraki, Y. et al. 1999 Suppl. Prog. Theor.
Phys. 133, 233). Such a telescope could monitor southern fields
essentially continuously, thus avoiding the not inconsiderable
difficulties associated with combining data from different
groups using different telescopes and different passbands,
and working under different seeing conditions. Losses of data
due to inclement weather would also be less serious. To monitor
the complete peak of a typical high magnification event from
the Antarctic would require good weather for a few days in
one location only. Presently, good weather is required simultaneously
in Chile, in Australasia and in South Africa. By observing
in the infrared, and taking advantage of the exceptionally
dry conditions at the Antarctic, one could extend the present
measurements to include the centre of the Galaxy. Gould has
pointed out this would increase the total event rate (Gould,
A. 1995b ApJ 446, L71). A 2-m class telescope would be
the preferred option to extend the current observations
being made with 1-m class instruments. US and Australian groups
have already made considerable progress towards the development
of the Antarctic for infrared astronomy (Burton, M. 1996 PASA
13, 2). Observations have been made from the South Pole which
confirm its excellent characteristics at infrared wavelengths,
and site-testing is in progress at Dome-C, which promises
to be even superior. In view of the above, Dome-C would
seem to be a promising site for future development of gravitational
here is some additional information on microlensing from Burton
et al 2001, Pub ASA, in press
micro-lensing occurs if the geodesic from a star to us passes
sufficiently close to a massive, foreground object that its
path is bent, or lensed, splitting the light into multiple
images (Paczynski, ApJ, 301, 503 (1986)). If there is a planet
near one of the images an additional lensing effect can occur
(Gould and Loeb ApJ, 396, 104 (1992)). The amplitude and light
curve of such an event depends on the geometry of the orbit
and mass of the planet, but typically will cause a perturbation
on the microlensing light curve with a magnitude of a few
percent for a few hours. If there is a planet present in the
lensing system the probability of detecting a lensing signature
from it is reasonably high if the sampling is frequent and
the photometric accuracy high (Albrow et al., ApJ. 512, 673
maximize the possibility of finding such events a dedicated
telescope should continuously image the same region of sky
where the stellar density is high. Nowhere is this more so
than towards the Galactic centre. Furthermore, the Galactic
centre becomes readily detectable at 2.4um (extinction precludes
observation at much shorter wavelengths), the very waveband
where the sky background is lowest in Antarctica. Moreover,
the Galactic centre is always visible from the South Pole.
For example, a 2-m telescope equipped with only a single 1024x1024
array with 0.6-arcsec pixels, mosaicing on a 4x4 grid, could
image a 40x40 arcmin region roughly every 20 minutes, achieving
a sensitivity of ~17.5 mags at 2.4um. Towards the Galactic
centre every pixel would contain at least one star! As calculated
by Gould (ApJ, 446, L71 (1995)), the optical depth for lensing
is then unity; i.e., we would always expect to find at least
one lensing event underway. Such a facility would be a powerful
tool for exploring the incidence of planetary systems through
the secondary lensing signature imposed on the micro-lensing
stellar spectropolarimetry - Brad Carter, USQ
the DMT is primarily envisaged as an infrared telescope, it
has some interesting applications for optical stellar spectroscopy
DMT's principal advantage will be its ability to continuously
monitor a star. Continuous and complete spectroscopic coverage
of all rotational phases of an active star is:
simplest way to map stars with rotational periods around
best way to map any active star with rapid active-region
best way to measure starspot differential rotation (a key
dynamo parameter), and
matching ground-based observations for multi-wavelength
around-the-clock observing campaigns utilising space observatories.
photometric precision could also yield the first direct observations
of starspots for moderately active sun-like stars, whose optical
and infrared variability is very hard to detect, yet is directly
relevant to the question of solar variability.
optical stellar spectroscopy, the DMT could be instrumented
relatively cheaply with an instrument perhaps similar to the
high efficiency "ESPaDOnS"
spectrograph/spectropolarimeter now under development by Jean-Francois
Donati, Claude Catala and John Landstreet for the CFHT.
high efficiency of ESPaDOnS on a 2m telescope would match
the 4m AAT with UCLES, and if the 2m was at Dome C, the above-mentioned
advantages would greatly enhance its potential.
more information on the science possible with an ESPaDOnS
clone, see this
stellar oscillations from Antarctica - Tim Bedding, USyd
aim of measuring stellar oscillations is to obtain a detailed
picture of the insides of stars by measuring the frequencies
at which they pulsate, in exactly the same way that seismologists
have used earthquakes to probe the interior of the Earth.
pulsate in many different modes simultaneously, each with
a slightly different period. Click
to see some animations of pulsating stars. Each mode is a
sound wave, so the periods give information about the sound
speed inside the star.
example, during its life, a star burns hydrogen into helium
in its core. The speed of sound in helium is less than in
hydrogen, so the pulsation periods of a star increase as it
gets older (its voice deepens!). Thus, measuring pulsations
and comparing with theory allows us to measure the ages of
study of starquakes, a field known as asteroseismology, has
until now been almost impossible because of interference from
the Earth's atmosphere. The twinkling of stars may be great
for poets and lovers, but it is extremely frustrating for
astronomers. It is caused by the movements of the air above
us, and has nothing to do with variations in the stars themselves.
offers the advantage of very much reduced scintillation. A
telescope in Antarctica should therefore be able to measure
stellar oscillations with a precision only surpassed by a
space telescope. An additional advantage is that almost
continuous observations will be possible. This is important
when trying to disentangle the different oscillation modes.
Telescopes at lower latitudes can only observe during fixed
periods each day (i.e., night time), leading to aliasing effects.
planets - John Innis
high-photometric precision expected of the proposed DMT, due
to reduced scintillation, will have great applicability to
photometric studies searching for and studying planets around
stars other than our Sun. Potential work falls into three
for new exo-planets by looking for the signature of the
transit of the planet across the face of the parent star.
A clear detection of the eclipse of the parent star by a
'hot-Jupiter'-planet from ground-based data has been reported
for the star HD 209458 (Charbonneau et al., Ap.J., 592,
L45-L48, 2000), where the eclipse depth was of order 0.01
magnitude. High-photometric precision is clearly needed.
The excellent site characteristics of Dome C would allow
searches to be extended for smaller planets (shallower
additional, high-quality, multi-wavelength data of known
eclipsing planet-star systems to observe the fine details
of the transit, including limb-darkening effects at the
different wavelengths. The extremely intriguing possibility
exists for the detection of the secondary eclipse -
i.e. the drop in light resulting from the disappearance
of the planet behind the star - implying a direct detection
of planet itself. Charbonneau et al (op cit) estimate that
for HD 209458, at IR wavelengths, secondary eclipse may
be 3 milli-magnitudes. High-precision photometry from an
excellent site should enable this to be seen. As the time
of primary eclipse will be known, along with the orbital
period and eccentricity, the times of secondary eclipse
can be estimated. A number of observations from the calculated
times of secondary minima could be combined to further reduce
noise. This appears to be an extremely exciting possibility,
as multi-wavelength data could reveal information about
the planetary properties directly.
high-quality photometric data on exo-planet systems suspected
from radial-velocity data, in order to determine the parent
star's rotation period. One of the major ambiguities in
attempting to determine the mass of the unseen companion
from radial velocity data alone is that the inclination
of the orbit is usually not known. Hence there may be considerable
uncertainty as to whether the companion is a planet, brown
dwarf, or even a low mass 'normal' star (Han et al., Ap.
J., 548, L57-L60, 2001). If the parent star's rotational
period, P, can be measured, through the photometric detection
of a rotational modulation due to the passage of sunspot-like
activity over the disk (see Brad Carter's contribution to
this page), and with the assumption that the orbital and
rotational axes are parallel, or nearly so, the orbital
inclination, i, can be estimated directly from: sin
i = 0.02 P (v sin i)/ (R/R_sun), (Campbell and Walker, IAU
Coll. 88, pp5-18, 1985) where v sin i is the rotational
broadening (obtainable from the stellar spectra), R is the
star's radius (which can be estimated from the spectral
type, or from other methods), and R_sun is the solar radius.
Hence, such data will provide additional constraints on
the allowable range of exo-planetary masses.
Environment of Star Forming Complexes - Burton et al 2001
massive star formation is one of the most spectacular events
in the Galaxy, paradoxically it is poorly understood. This
is because of both the short timescales for the various stages
of the process, and because of the many interacting phenomena
for which it is hard to disentangle cause and effect. The
environment of such star forming complexes, which dominate
the southern Galactic plane, can be studied in the thermal
infrared through the spectral features from ionized, neutral
and molecular species that are present. HII and ultra-compact
HII regions can be traced in the Br alpha 4.05um line, even
when deeply embedded. Polycyclic Aromatic Hydrocarbons (PAHs),
organic molecules that are fluoresced by far-UV radiation
from the young stars and trace the edge of photodissociation
regions, are visible through a spectral feature at 3.3um.
They can be imaged at high spatial resolution, unlike other
prime tracers of these regions, such as the far-IR [CII] 158um
line. Excited molecular hydrogen emission, resulting from
either shocks or UV-fluorescence, can be imaged in the v=1-0
Q-branch lines at 2.4um, which are both stronger and suffer
less extinction than the commonly used 1-0 S(1) line at 2.12um.
Several solid state absorption features are also present,
for instance the ice band at 3.1um.
an example of the potential for this kind of study, the following
image shows shows an 18 x 18 arcminute region of the star
forming complex NGC 6334, observed with the SPIREX/Abu camera
from the South Pole (Burton et al. ApJ, 542, 359 (2000)),
in the PAH and Br alpha features, as well as in the L-band
continuum at 3.5mu. The pixel scale in this image is 0.5 arcsec,
and combining the 1.5 arcsec diffraction limit with 1 hour
of unguided tracking, the typical resolution achieved was
~3 arcsec. Shells of photodissociated gas surround bubbles
of ionized gas in which embedded, massive protostars reside.
Despite the modest size of the SPIREX telescope (just 60cm),
these are the deepest images yet obtained at these wavelengths
at this spatial resolution. The small aperture, however,
also made possible the wide field of view with a similarly
Population Census of Star Forming Regions - Burton et
key goal for studies of star formation is to undertake a complete
population census of star forming clouds in order to determine
the number and types of stars that form in them, and how this
varies between different complexes. To do so requires observations
in the thermal infrared (beyond 3um). These wavelengths not
only penetrate to the depths of cloud cores, but also allow
us to distinguish between the embedded population and background
stars. In simple terms, young stellar objects are surrounded
by warm (few hundred K) disks which emit strongly at wavelengths
greater than 3um, and thus are readily distinguished in infrared
colour-colour diagrams (e.g., [1.65-2.2um] / [2.2-3.8um])
from reddened stars. Near-IR colour-colour diagrams (e.g.,
[1.25-1.65um] / [1.65-2.2um]), while relatively easy to construct
because of the better sensitivities available, show only small
IR excesses from the disks. These excesses are readily confused
with reddening, and the surveys fail to identify the most
deeply embedded sources.
problem has been that at 3.8um sensitivities are typically
4-5 magnitudes worse than at 2.2um from most observing sites,
thus limiting the work that has been done in this waveband.
Needed are deep, wide-field surveys of comparable sensitivity
to those conducted at 2.2um in order to determine the complete
stellar membership of a star formation region. Such an opportunity
is afforded by an Antarctic telescope through the greatly
reduced thermal background at these wavelengths over temperate
dwarfs - cool sub-stellar objects - may also be identified
through the deep absorption band at 3.4um, using narrow band
filters on and off the band to determine "colours". Even cooler
protostellar objects would be detectable in the mid-IR, for
instance embedded sources within "hot molecular cores" (e.g.,
Walsh et al. MNRAS, in press, (2001)), suspected of being
the first stage in the process of massive star formation.
Imaging through narrow band (1um wide) filters at 8.5, 10.5,
and 12.5um, where the background is at a minimum in the mid-IR
window, will allow determination of spectral colours of these
cooler objects, and thus help to place their evolutionary
and the First Star Formation - Burton et al 2001
star formation history of the Universe is being probed through
deep pencil-beam surveys, of which the Hubble Deep Fields
(HDF, Williams et al. AJ, 112, 1135, (1996)) are the most
prominent examples. At the faint end of the samples the relative
number of peculiar or disturbed galaxies rises dramatically,
suggesting that processes to do with star formation (e.g.,
mergers, starbursts) are active in these sources. However,
these galaxies also correspond to the most distant in the
samples, with the highest redshift, and in the visible the
rest frame being imaged is that of the far-UV. Here star formation
is not at its most apparent, and dust absorption can be significant.
An Antarctic telescope can search extraordinarily deeply
in the 2.4um "cosmological window" to where, for example,
the H alpha line is red-shifted at z=3. It could undertake
the first high spatial resolution, wide-field surveys at 3.8um
(L-band), where the visible light from z=5 galaxies would
be observed. While the magnitude limit of the HDF (I ~ 28
mags.) will remain far deeper than that which an Antarctic
2m telescope will reach at 3.8um (L ~ 19 mags. in 24 hours),
the colours of high-z galaxies are particularly red. For instance,
an E/S0 galaxy at z=1.4 has an unreddened colour of V - L
~ 10. Thus a galaxy with V=28 and L=19, barely detectable
in the HDF, would be detectable with an Antarctic 2m telescope
in a day of integration. Moreover, redder and presumably more
interesting galaxies, not seen in the HDF, would also be detectable.
of Proto-Stellar Disks and Jovian Planets - Burton et
of the great challenges facing astronomy, and the focus of
major national programs such as NASA's Origins program, is
the search for Earth-like planets. Several grand design projects
have been envisaged towards this goal, for instance NASA's
Terrestrial Planet Finder (Beichmann, Woolf and Lindensmith
(editors), "The Terrestrial Planet Finder (TPF)", NASA JPL-publication
99003 (1999)) and ESA's Darwin (Penny et al., Proc. SPIE,
3350, 666, (1998)). These are space-based nulling interferometers,
a suite of telescopes operating in mid-infrared where the
unfavourable contrast between star and planet is least. Such
facilities are not likely to be built before the middle of
the 21st century, and many major technological issues remain
to be addressed first. Several ground-based interferometers
are now under construction, such as the Very Large Telescope,
the Large Binocular Telescope and the Keck Telescopes, with
the intermediate goal of imaging circumstellar disks, zodiacal
dust and Jovian planets in nearby stellar systems. An Antarctic
infrared interferometer (AII) is an obvious next step after
a 2m class telescope, exploiting the reduced background, the
improved sky stability compared to temperate sites, and the
constant airmass of sources. We envisage the AII as a suite
of 2m size telescopes, initially with just two connected interferometrically,
but readily expanded for relatively low cost by the addition
of more telescopes, to explore the optimal configuration for
imaging other solar systems. It would provide the most powerful
ground-based instrument for this purpose.
Star Formation Rate in the Local Universe - Stuart Ryder,
DMT will be a powerful tool for surveying the true rate of
massive star formation in nearby (z<0.03) galaxies, through
measurement of the Br-alpha line flux at 4 microns. Traditionally,
the star formation rate has been estimated from the H-alpha
line in the optical (Kennicutt 1983, ApJ, 272, 54; Ryder &
Dopita 1994, ApJ, 430, 142), but the variable amount of dust
extinction leaves an uncertainty in the star formation rate
of at least a factor of 2 for any one galaxy. Surveys at radio
wavelengths do not suffer from extinction, but are subject
to variable contamination from non-thermal emission sources
(AGN, etc.) By going to 4 microns, the extinction is reduced
to less than 10% that at H-alpha, with a consequent reduction
in the extinction uncertainty. Although the atmospheric transmission
in Antarctica is not significantly better than a site like
Mauna Kea at 4 microns, the reduced thermal background from
the sky and telescope makes the DMT easily competitive
with an 8m on Mauna Kea, for the kind of wide-field survey
proposed here (see Table above).
would envisage using a tunable filter (akin to UNSWIRF) to
image the Br-alpha line and nearby continuum for a large sample
of galaxies out to a redshift of 7500 km/s (after which the
atmospheric transmission drops off precipitously), but this
would easily allow a much improved knowledge of the local
current rate of star formation (and its variation with galaxy
type, and environment) than is presently assumed. Such a survey
can be extended to higher redshifts by observing the Pa-alpha
line when it is redshifted away from its rest wavelength of
1.88 microns (where the atmosphere transmits poorly) into
the region of the K-band beyond 2.25 microns (z>0.2), where
the DMT excels.
infrared windows into the star formation properties of normal
spiral galaxies that have recently been opened up by the ISO
satellite include the 20-42 micron continuum (Dale et al.
2001, ApJ, 549, 215), the 7 micron continuum (Dale et al.
2000, AJ, 120, 583), and the so-called "aromatic features
in emission" between 5.5 and 13 microns (Helou et al. 2000,
ApJ, 532, L21). All of these windows are in regions of the
spectrum where the DMT is expected to easily compete with
much larger ground-based telescopes, and even with existing
gamma-ray bursts from Antarctica - Carl Akerlof, U. Michigan
years after their serendipitous initial discovery by satellites
designed to detect clandestine tests of nuclear weapons, gamma-ray
bursts (GRBs) are now understood to be incredibly powerful
explosions occurring at cosmological distances. The extreme
physical conditions that must exist in these events strain
the most imaginative attempts to find a reasonable theoretical
description. This is an area of science that is clearly data-driven.
In light of the diverse behavior of GRB light curves and the
large range in apparent luminosity, we are unlikely to reach
a deep understanding of this phenomena until a large sample
of these events can be observed in a broad range of wavelengths.
The significant breakthrough in this effort has been the determination
of precise X-ray coordinates by the Beppo-SAX mission, paving
the way for optical observations and spectroscopic measurements
of red shifts. After four years, there are still less than
twenty GRBs that have been optically observed and a whole
sub-class, short duration bursts, have not been seen at all.
Of the X-ray observed events, only 50% have been correlated
to an optical signal, leaving open the question of why this
ratio should be so low. Finally, the extremely high intrinsic
brightness of GRBs raises the possibility of using these events
as probes of the early Universe as star formation became significant.
The fact that GRB990123, at a red shift of 1.61, was one of
the most intense bursts ever seen in gamma-rays and reached
an optical brightness with mv < 9 shows that these events
should be detectable at much higher red shifts, far deeper
than we can probe with supernovae.
proposed Douglas Mawson Telescope (DMT) has some unique characteristics
that would greatly improve our ability to observe gamma-ray
bursts at longer wavelengths. The location near the South
Pole gives it one outstanding advantage - it is possible during
the Antarctic winter to continuously monitor a specific burst
for as long as patience will allow. This means that extensive
light curves can be obtained from a single instrument without
the systematic problems that beset present attempts. With
imaging sensors that extends deep into the infra-red, this
instrument is likely to find counterparts either hidden by
dust or molecular clouds or at red shifts inaccessible with
silicon CCDs. Although space-born telescopes have the advantage
of working outside the glow of the atmosphere, such expensive
missions cannot devote extensive observing time to one particular
research program. If the DMT can be engineered with reasonably
rapid slew, it will have another advantage - access to the
optical burst phase such as viewed by the ROTSE project for
GRB990123. Because of the torque requirements and the complexity
of safely reorienting a spacecraft, this observing niche must
remain solely in the domain of ground-based instruments. There
are two new robotic 2-meter telescopes that have rapid slew
capability; both of them lie in the northern hemisphere (La
Palma and Hanle, India). The number of events that can be
monitored per year can be estimated fairly reliably. The SWIFT
mission which is expected to launch around 2004 should identify
~300 events per year with accuracies of the order of a few
arc-minutes. With a target-of-opportunity observing program,
at least 20 events should be accessible for prompt observations
- this might be significantly higher since deep IR imaging
can be performed under daytime conditions. The most exciting
possibility is that the DMT will be able to detect bursts
at distances that far exceed anything we know about today.
Lamb and Reichart (Astrophysical Journal 536, 1-18) have calculated
that the SWIFT GRB mission will be sensitive to red shifts
in excess of 70. Coupled to estimates of the early star formation
rate, it is likely that a significant number of bursts can
be optically detected at red shifts between 5 and 10. Such
a discovery would open a new window to understanding the evolution
of the Universe.
interferometry in Antarctica - James Lloyd & Ben Oppenheimer,
Lower boundary layer turbulence at the South Pole degrades
the seeing from the superb free atmosphere value. At sites
such as Mauna Kea or Paranal the seeing is primarily caused
by turbulence at altitudes of 10-20km.
it happens that the mean square error for an astrometric measurement
with a dual beam differential astrometric interferometer in
the very narrow angle regime is proportional to the integral
of h^2 C_n^2(h). Therefore, sites at which the turbulence
occurs only at low altitudes offer large gains in astrometric
programs that would benefit greatly from such an instrument
include planet detection, microlensing by dark matter candidates,
studies of the mass and dynamics of the galaxy, and fundamental
astrophysical measurements such as stellar properties and
the cosmic distance scale.
a Hufnagel-Valley turbulent atmosphere model that fits Rodney
Marks' South Pole median low altitude data gives an astrometric
error of 4 microarcsec for a 1 hr integration with a 100m
baseline for stars separated by 1 arcmin. The same interferometer
at Mauna Kea with Roddier's 1990 "typical" Scidar profile
gives 50 microarcsec accuracy. This gives an Antarctic
interferometer a factor of 12 increase in accuracy, or a factor
of 144 in speed.
Keck interferometer, SIM and the VLTI are all planning extensive
astrometric science projects. Some scientific ighlights for
an antarctic interferometer might be:
http://sim.jpl.nasa.gov/science/planet.html). The important
things to know about planet detection:
signature at 10 pc is about 1 milliarcsec.
Earth's is about 1 microarcsec.
signatures decline as 1/d
will never see the Earth's orbit unless you model out
Jupiter's (see the figure on the SIM web page). This
means that a 5 year mission (e.g., SIM) would cover
an insufficient time interval to fully model a solar-like
planet detection, a factor of 12 in accuracy translates
factor of 12 in detectable mass, or
factor of 12 in distance at which a given system can
be detected, or
factor of 1700 in volume to search!
144 times increase in sky area from which to select
of Microlensing towards the LMC
is a controversial body of evidence that suggests that
a substantial fraction of the dark matter in the Milky
way is in the form of old white dwarfs. These may have
been detected by microlensing, and direct surveys. Astrometry
of the microlensing events is sufficient to determine
the distance to the lens, and therefore determine whether
the LMC microlensing lenses are in the Halo of our Galaxy.
The LMC is also uniquely suited as a prime target for
the distance to the LMC, perhaps even by direct parallax.
design of the DMT with near-IR imager - Peter Gillingham
made a preliminary study of the performance to be expected
from a Ritchey Chretien telescope with a 2 metre diameter
primary mirror imaging directly onto an array in the K'
and L infrared windows.
figure below shows the telescope. It has a primary focal
ratio of f/2, a final focal length of 12m, and a back
focus (distance from primary vertex to focus) of 700mm.
The secondary is made undersized so that light from outside
the primary is not reflected by the secondary anywhere
within a 30 arcmin diameter field. The secondary diameter
is 560 mm and the diameter used on the primary for any
one point in the field is 1894mm, making the final focal
ratio f/6.34. The scale is about 58 microns/arcsec.
an optimum choice of primary and secondary asphericities
(the Ritchey Chretien condition) coma-free images are
formed on a surface with radius of curvature 1234 mm.
For a plane detector, a reasonable compromise focus can
be set for a field radius up to about 10.6 arcmin. The
figure below shows the diffraction based images with their
Strehl ratios for this case. The K' window is represented
by wavelengths 2.3 and 2.6 microns and the L window by
3 and 4 microns. Note that the boxes are 100 microns on
a larger field with a plane detector, it is necessary
to flatten the field optically. The figure below shows
the layout with a meniscus field flattener of CaF2 just
ahead of the detector.
figure below shows that, with this arrangement, images
with little degradation compared with the diffraction
limits are obtained to the full 15 arcmin radius.
the scale at the Ritchey Chretien focus already suits
high resolution imaging with an IR array having pixels
about microns square,
there is little requirement for spectroscopy, and
the telescope environs will be very cold,
is likely (as suggested by Peter McGregor at the DMT Science
Workshop on 4 May 2001) that re-imaging the telescope
pupil onto a cold stop can be avoided. In the first figure
above, the locations are indicated where a cold baffle
(inside the IR dewar) and "warm" Narcissus mirrors might
be put. With suitable choice of the locations and radii
of curvature of these mirrors, it is possible to ensure
that no part of the field is exposed to any radiation
from telescope surfaces either directly or via reflection.
figure below shows how effective Narcissus mirrors could
be in the case where the field is 15 arcmin square (roughly
filling a 2k x 2k array). Extraneous skylight, passing
directly to the detector without reflection from the primary
and secondary mirrors, is limited to about 20% addition
to the unavoidable sky background, without vignetting
of Narcissus mirror in excluding extraneous sky
example above, giving ~ 20% additional sky radiation,
was for a 2k x 2k x 18um array. In theory, the excess
radiation would halve for a 1k x 1k array (and double
for 4k x 4k). One could reduce the percentage of excess
radiation by accepting some vignetting; e.g. for the 2k
case, making the narcissus mirror aperture match the circular
beam profile for the on-axis case would result in vignetting
and excess radiation each grading from 0 at the field
centre to about 6% at the corner of the field. For a 1k
array especially, the sky exclusion would, I think, be
very little inferior to that of a system with imaging
onto a cold stop. Its efficiency, freedom from ghosts,
and cost would be very favourable.
imagined offset guiding would be done using either small
CCDs or fast IR arrays set next to the sides of the IR
array, inside the Dewar.
note from the 13 Oct '98 letter to Gatley from Greenhouse
(NGST Deputy Project Scientist) appended to the Report
to the OIR Panel of the Decadal Committee..., "Infrared
Astronomy at the South Pole" that NGST were meaning to
use 4k x 4k InSb arrays. Depending on its pixel size,
the diagonal of such an array might cover about 30 arcmin
at 12 metre focal length.
think an equatorial telescope at latitude 75 deg, ie.
an alt-az with its az axis tilted 15 deg., would be little
more complicated than an untilted alt-az. Avoiding the
necessity for an instrument rotator and having a non-rotating
psf seem worthwhile. However, I think it would be highly
desirable to have fine adjustments of the polar axis tip
and tilt motorised (somewhat like the polar axis elevation
of the UK Schmidt, but for different reasons). I suspect
the ice foundation, even if it's not built up 150 m above
the plateau, will drift in angle sufficient to need correction
several times a year for the most critical "wide field"
Ritchey Chretien optical system with a field flattener
can give virtually diffraction limited performance in
K' and L across a flat field 30 arcmin diameter with the
aid of a simple field flattening lens.
a 2k array about 38mm square, no field flattener is needed
and Narcissus mirrors can limit extraneous radiation directly
from the sky to about 20%, without vignetting the field.
This leads to a very simple system for direct imaging.
Asked Questions and Common Misconceptions
does the DMT compare with other planned and proposed facilities?
DMT, as a 2m size telescope, is a relatively cheap facility,
costing less than 5% that of large optical telescopes,
or the airborne and space-facilities being planned by
other countries. Nevertheless, the unique environment
of Antarctica allows it to undertake a range of science
that is competitive with these facilities.
wavelengths beyond 2.3 microns the DMT is as sensitive
as an 8m telescope on an excellent site like Mauna Kea,
for imaging extended sources (ie when measuring flux per
unit area). It is, however, considerably easier to image
large fields of view. Thus, for wide-field thermal infrared
imaging an Antarctic 2m would out-perform existing telescopes.
It can therefore attempt a range of projects that are
complementary to those larger facilities (for instance,
surveying wide areas surrounding fields imaged by the
larger facility), as well as many that would not be undertaken
with an 8m (for instance, mapping the Galactic ecosystem).
point-source imaging, if the diffraction limit can be
achieved then invariably the larger the telescope used
the greater the sensitivity achievable, because the background
noise signal is obtained from a smaller region of sky.
If, however, the full-diffraction limit of the telescope
is not achieved by the larger telescope that gain is rapidly
lost over an Antarctic telescope, where the background
levels are typically 20 times lower in the infrared.
facilities such as SIRTF, SOFIA and NGST, while they will
each achieve superb performance in their own areas, still
remain virtual facilities that are subject to descoping.
SOFIA has recently been delayed a further two years due
to budgetary considerations. NGST has just had its long
wavelength functionality considerably descoped. SIRTF
has had its specifications fixed for some time. It is
yet to be launched and its operations then entail some
considerable risks. While in areas of overlap a ground-based
facility cannot achieve the sensitivities of a cryogenic
space telescope, SIRTF is a relatively small facility
with a spatial resolution of, at best, of 2.4 arcseconds.
In the science wavebands of relevance to the DMT, SIRTF
has just four fixed broad band filters, at 3.6, 4.5, 5.8
and 8 microns. There are no line filters, for instance,
to measure molecular hydrogen, PAHs or ionized hydrogen.
will be a superb facility, nevertheless. It is going to
open up new areas of study, particularly at far- infrared
wavelengths, which cannot be accessed from the ground.
Rather than complete all science that is possible at thermal
infrared wavelengths, SIRTF is going to stimulate great
demand for follow-up projects, projects for which the
time available with SIRTF was insufficient to undertake
and projects for which its instruments were incapable
of attempting. Historically, the age of space observatories
has resulted in greatly increased demand for ground-based
follow-up. HST has stimulated the demand for optical 8m
telescopes, for instance. In the thermal-IR there are
few other facilities anyway, so that demand for those
that exist is expected to be intense once SIRTF is launched.
access to SIRTF, and later to SOFIA and NGST, will be
extremely limited in any case as we have no national involvement
in these facilities. The DMT, as one of the few facilities
available which allows follow-up projects to be conducted,
therefore provides Australia with an opportunity to trade
time for access to the other facilities.
work in the thermal infrared?
date there has been little work done in Australia in the
thermal infrared part of the spectrum. In large, this
is due to the difficulties of working in this waveband,
the Australian mainland not having any really good sites
for working beyond 3 microns. However, even at major observatory
sites like Mauna Kea, working beyond 3 microns is still
hard, and relatively few groups have concentrated their
science there. The scientific potential for infrared investigations,
however, is not questioned. The birth of planets, stars
and galaxies can only be seen in these wavebands. The
importance that has been attached to observing in the
infrared can be judged by the fact that several nations
are now investing in major infrared facilities like SIRTF,
SOFIA and NGST, facilities that can cost over two orders
of magnitude more to build than the DMT.
the frontiers of astronomy keep advancing we need to move
forward too if we wish to participate at its leading edge.
A century ago cutting-edge science involved measuring
the orbits of double stars. A decade ago it was spear-headed
by the 4m optical telescopes like the AAT. In the coming
decade it will involve the infrared.
work in the sub-millimetre?
reasons are similar to those given above for the infrared.
It is impossible to work in this regime from Australia.
It remains difficult to observe in it from Mauna Kea.
Yet the first signatures of proto-galactic and proto-stellar
collapse are given out in the sub-millimetre. Technological
advances in receiver and telescope design now make it
feasible to consider interferometric arrays operating
in the sub-millimetre, the most notable being the one
billion dollar ALMA project (planned for the Atacama in
Chile). Australia currently has no expertise in this area
even if we wished to participate. The Antarctic plateau
does, however, provide the best locations for sub-millimetre
astronomy on the Earth. It would be particularly suitable
for a single- dish telescope, complementing ALMA, and
even observing in some windows that will remain closed
to ALMA (eg at 200 microns).
is also rapidly developing skills in millimetre astronomy,
through both the Mopra telescope and the forthcoming millimetre
interferometer on the ATCA. Sub-millimetre astronomy in
Antarctica provides a natural confluence connecting the
interests of the optical/IR and radio communities in Australia,
and will also provide us with the skills and ability to
contribute in the future to ALMA.
important is high spatial resolution?
resolution is, of course, exceedingly important for a
wide range of astronomical observations. The DMT, by virtue
of its size, would not be able to compete with an 8m telescope
in this regard. This is why the initial scientific focus
will be on wide-field studies, where areas of sky typically
two orders of magnitude greater than observable with an
8m could be studied.
requiring the highest spatial resolution for their projects
would continue to use Gemini, though they only have a
handful of nights available each year to do so, and so
any such projects are somewhat restricted in their scope.
the best resolution will be obtained by an interferometer,
not a single telescope. The superior phase stability of
the sky makes Antarctica an attractive location for a
mid-infrared interferometer, needed to resolve proto-planetary
disks and zodiacal clouds around stars.
does the seeing affect performance?
ice-level seeing at the South Pole is relatively poor,
about 1.5 arcseconds in the visible, comparable to Siding
Spring. It is however, confined to a narrow inversion
layer, some 200m thick. This leads to an isoplanatic angle
of about 1 arcminute, some 30 times greater than achievable
on Mauna Kea, where the turbulent layer arises in the
jet stream. This greatly facilitates adaptive optics correction,
with longer coherence times, most of the sky containing
stars bright enough to be used for AO correction, and
of course a one arcminute corrected field of view. Moreover,
there is every expectation that at high plateau sites
such as Dome C the boundary layer will be even thinner,
raising the possibility that a telescope could be placed
on a raised tower above it, avoiding most of the seeing
accurate photometry possible?
proximity and narrowness of the turbulent boundary layer
also implies that scintillation will be considerably reduced
from temperate-latitude sites. Since scintillation noise
is a major limitation to precision photometry (ie at the
milli-magnitude level), this opens up several fields where
this level of precision is required, for instance exo-solar
planet detection via occultations and stellar seismography.
much better can we do microlensing experiments in Antarctica
experiments in the optical have obviously been done exceedingly
effectively in Australia, notably from Canberra, Hobart
and Perth. However it is not possible to obtain a unit
depth to lensing within a field (i.e., to have enough
stars in the field so that a lensing event is always going
on) unless viewing the Galactic centre, and this necessitates
infrared observations in order to reduce the extinction
sufficiently for the stars to be seen. At 2.35 microns
all the stars towards the Galactic centre can be seen,
and moreover this is the very wavelength where the background
is lowest, between the thermal emission at longer wavelengths
and airglow emission to shorter wavelengths. For planet
searches it is essential to have both fine time resolution
(the secondary events due to planets might only last minutes),
over extended periods of time (so the source must be continuously
visible) and enormous numbers of sources to work on (requiring
a sight line towards the Galactic centre). All these conditions
can be uniquely met from Antarctica.
does the DMT maintain our ability in astronomical technology?
is a challenging environment, and operating in it requires
novel solutions to some engineering problems, and attracts
the best engineers to solve them. Moreover, innovative
engineering solutions often have commercial spin-offs
in unrelated areas, which enhances their value considerably.
optical telescopes have got larger the size of their instruments
has expanded considerably. The number of institutions
that can hope to build them has correspondingly diminished,
and they are now beyond the capabilities of all but the
largest groups. In Australia only at Mount Stromlo and
the AAO are there groups capable of undertaking instrument
projects for an 8m telescope. A 2m telescope, such as
the DMT, requires a relatively small instrument, presenting
a project which is within the capability of university
groups. Research groups will once more be able to contemplate
building an instrument to focus on a particular area of
interest. This will contribute to Australia maintaining
a vibrant research community across a range of institutions.
does global warming and the shrinking polar ice caps affect
will be no significant change to the polar ice caps
in the next ten years. Icebergs come and go along the
coast, but then, they always did.
models predict an increase in global hunidity, which
harms the sites in Chile and Hawaii. The relative humidity
at Dome C is already 100% (although the absolute humidity
is, of course, miniscule), so the increased global humidity
won't affect the atmospheric transmission.
increased global humidity will cause an increase
in the height of the polar cap (because it is such an
efficient cryopump). Dome C will get even higher.
100 years from now, Dome C will be even better and Chile
and Hawaii even worse. Meanwhile, both Sydney and Melbourne
will be under 10 feet of water, and infrared astronomy
will be the least of our concerns...
difficult is it really to work in Antarctica?
is no doubt that Antarctica provides a challenging environment
in which to work in. However much of difficulty is perceived,
and arises from the fear of the unknown. Australia now
has a decade of experience working on a range of astronomical
instrumentation at the South Pole, and has worked closely
with the USA over that time, sharing many ideas along
the way. The main problems are thermal issues, and these
are now well understood. In fact Antarctica has many features
that make designing telescopes easier than at temperate
sites. These include:
low wind speeds on the plateau
is not a problem
is no need for a dome to keep the rain off
is no dust
telescope can be left open to the elements throughout
addition to the AASTO and the SPIREX telescope that Australia
has had direct involvement in, there are a number of other
successful telescopes with sophisticated instrumentation
operating at the South Pole, which show that the challenges
can indeed be met. These include the VIPER and DASI CMBR
experiments, the AST/RO sub-millimetre telescope and the
AMANDA neutrino telescope.
much time could the telescope be used for? Can it be used
in the summer months?
experiments could obviously only be undertaken in winter
months, and there are only about 4 months for which the
sky is truly dark. However, in the thermal infrared there
is little difference between day time and night time conditions,
and the longer the wavelength the less the difference
is. For instance, the published image of the PAHs emission
in Carina (Brooks et al, MNRAS, 319, 95-102 (2000)) was
obtained during November, ie the South Pole summer. Thus
the primary science the DMT would perform could be undertaken
at any time of the year. In practice, of course, during
the summer time would also be devoted to telescope maintenance
and instrument upgrades, but once the telescope is fully
operational only instrument changes would limit full-time
science is driving the desire for an interferometer?
themes, such as the search for another Earth, are increasingly
driving the directions of several major national programs.
To meet their objectives it is necessary to construct
a mid-IR interferometer, where the signatures of an Earth-like
planet are believed to be clearest. Grand-design experiments,
such as NASA's TPF or ESA's Darwin, have been proposed
for this. These are tremendously challenging projects,
and will require a vast amount of preparatory work. Foremost
is the challenge of constructing a nulling interferometer.
The reduced sky emission and the improved phase stability
offered by Antarctica make this the most suitable location
for developing these techniques. Along the way an Antarctic
interferometer would also be able to undertake much valuable
science, from imaging proto-planetary disks to detecting
zodiacal clouds as a star evolves towards the main sequence,
to possibly directly detecting Jovian-sized planets orbiting
several AU from their parent star.
does the DMT lead to?
the DMT provides a range of fascinating science projects
that can be undertaken, it is also just an entry point to
Antarctica that lets us contemplate some truly exciting
science that could be undertaken with major facilities.
These include both large optical/IR telescopes, sub-millimetre
telescopes and interferometers. The DMT can be augmented
through a range of instrumentation and through construction
of further 2m-sized telescopes, each devoted to single major
projects. This is possible because the cost of the telescope
no longer dominates the cost of the project - a major instrument
could indeed cost more than the telescope itself. Further
on, a large optical/IR telescope might be built, and/or
several 2m telescopes connected together to form a mid-IR
interferometer. A possible scenario might be as follows:
DMT is built with a 3-5 micron thermal infrared camera
and a 1K array.
groups contribute individual instruments to the telescope.
These might include a mid-IR camera, 1-2.5 micron and
3-5 micron cameras with their 30 arcminute focal plane
tiled with arrays (for lensing studies, monitoring projects
and surveys), an optical echelle spectrograph mapping
stellar surfaces, and a sub-mm bolometer array. Each
instrument might be used for focussed in-depth investigations
(ie lasting 1-3 months), before the instrument is changed.
6.5m telescope, the Australian Large Telescope, Antarctic
(ALTA), is built. Its performance beyond 2.4 microns
would exceed that of the Keck for all possible observations.
This could be built in as little as 5 years after the
DMT, as the requisite expertise is now commercially
suite of 2m-sized telescopes are connected together
to form a mid-infrared interferometer, used both as
a testbed for developing the technology of nulling interferometry,
and to study the evolution of proto-planetary disks
into zodiacal clouds as planetary systems form around
the DMT none of these projects will be possible. It truly
is an entry point for a range of competitive projects
that will allow Australia to maintain its reputation as
a leading nation in astronomy and the associated high
technology. But if the DMT is not built the impetus and
initiative that Australia has established over a decade
of effort in Antarctica will be lost, as we watch others
capitalise on our pioneering endeavours.
29 July 2001, during the last day of the highly successful
Dome C workshop in Hobart, we learned that the DMT funding
proposal had been culled from further consideration.
note that our proposal included support from three industrial
partners and had operating and logistical costs for the
telescope guaranteed for 10 years by the French and Italian
this setback, and because of the strong support the proposal
has generated from other quarters, we are continuing to
pursue funding possibilites through other channels.
/ Michael Ashley / email@example.com