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CSIRO PUBLISHING www.publish.csiro.au/journals/pasa Publications of the Astronomical Society of Australia, 2005, 22, 199–235 Science Programs for a 2-m Class Telescope at Dome C, Antarctica: PILOT, the Pathfinder for an International Large Optical Telescope M. G. BurtonA,M, J. S. LawrenceA, M. C. B. AshleyA, J. A. BaileyB,C, C. BlakeA, T. R. BeddingD, J. Bland-HawthornB, I. A. BondE, K. GlazebrookF, M. G. HidasA, G. LewisD, S. N. LongmoreA, S. T. MaddisonG, S. MattilaH, V. MinierI, S. D. RyderB, R. SharpB, C. H. SmithJ, J. W. V. StoreyA, C. G. TinneyB, P. TuthillD, A. J. WalshA, W. WalshA, M. WhitingA, T. WongA,K, D. WoodsA, and P. C. M. YockL A School of Physics, University of New South Wales, Sydney NSW 2052, Australia B Anglo Australian Observatory, Epping NSW 1710, Australia C Centre for Astrobiology, Macquarie University, Sydney NSW 2109, Australia D University of Sydney, Sydney NSW 2006, Australia E Massey University, Auckland, New Zealand F John Hopkins University, Baltimore, MD 21218, USA G Swinburne University, Melbourne VIC 3122, Australia H Stockholm Observatory, Stockholm, Sweden I CEA Centre d’Etudes de Saclay, Paris, France J Electro Optics Systems, Queanbeyan NSW 2620, Australia K CSIRO Australia Telescope National Facility, Epping NSW 1710, Australia L University of Auckland, Auckland, New Zealand M Corresponding author. E-mail: [email protected] Received 2004 November 12, accepted 2005 April 12 Abstract: The cold, dry, and stable air above the summits of the Antarctic plateau provides the best ground- based observing conditions from optical to sub-millimetre wavelengths to be found on the Earth. Pathfinder for an International Large Optical Telescope (PILOT) is a proposed 2 m telescope, to be built at Dome C in Antarctica, able to exploit these conditions for conducting astronomy at optical and infrared wavelengths. While PILOT is intended as a pathfinder towards the construction of future grand-design facilities, it will also be able to undertake a range of fundamental science investigations in its own right. This paper provides the performance specifications for PILOT, including its instrumentation. It then describes the kinds of projects that it could best conduct. These range from planetary science to the search for other solar systems, from star formation within the Galaxy to the star formation history of the Universe, and from gravitational lensing caused by exo-planets to that produced by the cosmic web of dark matter. PILOT would be particularly powerful for wide-field imaging at infrared wavelengths, achieving near diffraction-limited performance with simple tip–tilt wavefront correction. PILOT would also be capable of near diffraction-limited performance in the optical wavebands, as well be able to open new wavebands for regular ground-based observation, in the mid-IR from 17 to 40 µm and in the sub-millimetre at 200 µm. Keywords: telescopes — site testing — atmospheric effects — techniques: high angular resolution — stars: formation — cosmology: observations 1 Introduction — the Antarctic Plateau dominates at wavelengths longer than 2.2 µm, is far less The highest regions of the Antarctic plateau provide a than at temperate sites (at shorter infrared wavelengths the unique environment on the Earth for conducting observa- emissivity is primarily due to OH airglow from the upper tional astronomy. This is because of the extreme cold, the atmosphere). A reduced concentration of particulates in dryness, and the stability of the air column above these the atmosphere lowers the sky emissivity (predominantly locations — leading to a lower sky background, greater arising from dust and aerosols at temperate sites), further transparency, and sharper imaging than at temperate sites. lowering the background at these wavelengths. Columns The Antarctic high plateau includes an area about the of precipitable water vapour are less than 250 µm for size of Australia, all of which is above 3000 m elevation. much of the year, opening atmospheric windows across With a year-round average temperature of −50◦C, falling the infrared and sub-millimetre bands. Wind speeds are as low as −90◦C at times, the sky thermal emission, which low at the summits of the plateau, with violent storms © Astronomical Society of Australia 2005 10.1071/AS04077 1323-3580/05/03199 Downloaded from https://www.cambridge.org/core. IP address: 170.106.35.229, on 02 Oct 2021 at 00:39:10, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1071/AS04077 200 M. G. Burton et al. non-existent. The thinness of the surface inversion layer, a International Large Optical Telescope — could tackle combined with the minimal turbulence above it, provides if it were built at Dome C. This 3250 m elevation site conditions of extraordinary stability, with the lowest levels is the location of the new Concordia scientific station of seeing on Earth. These conditions are also particularly (75◦S, 123◦E), built by the French and Italian national suitable for wavefront correction. The plateau also has the Antarctic programs (Candidi & Lori 2003; Storey et al. lowest levels of seismic activity on the planet. Together 2003) and opened for winter operations in 2005. This doc- with the low wind, this reduces constraints on the required ument also builds on two earlier science cases forAntarctic strength and stiffness of large structures. astronomy, the first when the program was beginning in Taken together, these conditions create an important Australia (Burton et al. 1994), and the second when the opportunity for observational astronomy, from the optical emphasis was on building the 2-m Douglas Mawson Tele- to the millimetre wavebands. Indeed, given the relative scope, which focussed on wide-field thermal-IR imaging ease of access compared to space, they may provide the (Burton, Storey, & Ashley 2001). best environment from which to conduct some grand- design experiments, such as the search for exo-earths, for the next several decades. Nevertheless, the astron- 2 The Advantages of Antarctica for Astronomy omy so far conducted in Antarctica has been largely As a result of extensive site-testing programs that have confined to just a few of the competitive niches (see, for been conducted at the South Pole for over two decades, and example, Indermuehle, Burton, & Maddison 2005). These at Dome C since 1996, it has been established that there include a series of successful cosmic microwave back- are a number of major advantages that anAntarctic plateau ground experiments and sub-millimetre astronomy with observatory would have over the same facility operating the modest aperture telescopes, together with, from par- at temperate latitudes. These include: ticle astrophysics, the installation of networks of cosmic • Low temperature: At wavelengths shortward of the ray facilities, the building of the first neutrino telescope, blackbody-like peak in the sky-emission spectrum, the and the collection of meteorites from blue-ice fields where flux drops considerably for a small fall in temperature. they have been transported to after falling onto the plateau. Above the Antarctic plateau the background reduction Aside from site testing, no astronomy has yet been con- relative to temperate sites, for a typical mid-winter ducted from any of the summits of the Antarctic plateau. temperature of −60◦C, is ∼20 times at near-infrared While there is no doubt that the performance of large wavelengths (2.2–5 µm) (Ashley et al. 1996; Nguyen Antarctic telescopes that operate in the optical and infrared et al. 1996; Phillips et al. 1999; Walden et al. 2005). This would be significantly better than that of comparable facil- is equivalent to obtaining the same sensitivity using a ities at temperate sites, so far the largest telescope to telescope of several times the diameter at a temperate observe in these wavebands has been the 60 cm SPIREX site (see Section 4.1.1). Between 2.27 and 2.45 µm the telescope at the South Pole (Hereld 1994; Fowler et al. background drop is even greater, around 50 times. 1998). The South Pole, however, at 2835 m, is on the flank • Low water vapour: With the precipitable water vapour of the plateau and suffers from the katabatic air flow off content averaging ∼250 µm above the plateau in win- the summit at Dome A, which disturbs the seeing in the ter (Chamberlin, Lane, & Stark 1997; Lane 1998), the surface inversion layer. Better sites than South Pole are atmospheric transmission is considerably improved, to be found on the summits of the plateau, in particular particularly at mid-IR and sub-millimetre wavelengths at the accessible site of Dome C. An intermediate-sized (Chamberlain et al. 2000; Hidas et al. 2000; Calisse telescope at Dome C is an important next step in Antarctic et al. 2004), over temperate locations. New win- astronomy, prior to investing in major optical/IR facili- dows become accessible for ground-based observation ties. Its successful operation would demonstrate that the between 20 and 40 µm and at 200 µm. In addition, the gains inferred from the site testing campaigns can in fact low water vapour also lowers the emissivity of the atmo- be realized. It would also allow the logistical and engi- sphere, further reducing the sky flux.At the very highest neering requirements of running such a facility through location on the plateau, the 4200 m Dome A, the water the Antarctic winter to be appraised. vapour content may drop below 100 µm at times, fur- Operating such an intermediate-sized telescope as a ther opening new windows right across the far-infrared technology demonstrator is only part of the requirement, spectrum (see Lawrence 2004a). however. The demands of scientific enquiry also mean that • Low aerosol contribution: The lack of dust and other it is essential that such a telescope be able to undertake particulates in the atmosphere greatly reduces the con- competitive science as well, even if its primary purpose is tribution to sky emissivity from aerosols (Chamberlain as a step towards more powerful facilities to follow.

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