Astronomy in Antarctica

Transcription

1 Astronomy in Antarctica Michael Burton School of Physics, University of New South Wales The Antarctic plateau provides the best conditions possible from our planet for a wide range of astronomical observations of the cosmos. This is on account of the extreme cold and the incredibly dry and stable air on top of the plateau, which reaches to 4,200m at Dome A, within the Australian Antarctic Territory. These conditions can only be bettered by telescopes placed in space. Australian scientists have been pioneering the development of the Antarctic plateau for astronomical investigation, quantifying the performance expected for astronomical measurements, and developing the expertise and technology for operation in the harsh environment. Their first expedition was to the 2,900m South Pole, in 1994, when the University of New South Wales collaborated with the US Center for Astrophysical Research in Antarctica (CARA) to start a site testing campaign in order to determine exactly how good the Antarctic plateau is for astronomy. The first experiment saw the IRPS, an instrument originally used on the Anglo Australian Telescope, placed on the roof of a laboratory and used to measure the brightness of the infrared sky over the depths of an Antarctic winter (see Figure 1) 1. As expected, the sky was the darkest ever measured for astronomical observation. Along with the IRPS, our US colleagues also installed a small infrared telescope, the 60cm SPIREX (South Pole Infrared Explorer), in order to take infrared images of the cosmos, and to demonstrate that sophisticated instrumentation could be successfully operated through an Antarctic winter. Initially this telescope only worked at short infrared wavelengths, less than 2.5 m. However, with the success of the sky measurement made with the IRPS, it was realised that somewhat longer wavelength infrared 1 This work is reported in the article 'South Pole observations of the near-infrared sky brightness', written by Ashley, M.C.B., Burton, M.G., Storey, J.W.V., Lloyd, J.P., Bally, J., Briggs, J.W. & Harper, D.A., published in 1996 in the Publications of the Astronomical Society of the Pacific, vol 108, pages

2 measurements would be better undertaken. The Australian scientists then teamed up with their US colleagues in order to install a new infrared camera on SPIREX, the Abu camera, which worked from 1 5 m (see Figure 2). In 1998 this was installed at the South Pole and observations made over the next two Antarctic winters. Figure 3 shows perhaps the most spectacular result of this work, an infrared image of the star forming region NGC 6334, which lies about 5,000 light years away in the southern galactic plane. The image combines three infrared wavebands from 3.3 m to 4.1 m, colour-coded from blue to red. The blue colour shows emission at 3.3 m from organic molecules, PAHs (or polyaromatic hydrocarbons), rings of carbon atoms linked with hydrogen atoms. They show up as shells of material, fluoresced by the strong ultra-violet radiation coming from powerful new stars being born in the cores of dense, dusty molecular clouds. Some of these stars can just be seen emerging from these cores, evident by the red colouring showing light at 4.1 m wavelength. 2 The image is illustrating aspects of the galactic ecology at work, the cycle of material between the stars and the gas of interstellar space that drives the evolution of our Galaxy. Here remnants of the natal material from which stars are born is being lit up by the infant stars themselves, now forming a stellar nursery. Despite the modest size of the telescope, the images taken by SPIREX in the infrared were, at that time, the most sensitive ever taken at those wavelength, testimony to the superb conditions for astronomy in Antarctica. Colder, higher and drier sites to the South Pole exist on the summits of the Antarctic plateau. In 2000 Australian scientists got the opportunity to venture to the 3,200m Dome C, where a French-Italian scientific station was under construction. This lies within the Australian Antarctic Territory, in the vicinity of the region first visited in 1909 by Douglas Mawson when he became the first person the visit the site of the South Magnetic Pole. An autonomous observatory, the AASTINO (Automated Astrophysical Site Testing Observatory) was built at the University of New South Wales, and shipped to Antarctica from Hobart, and then driven by tractor train to Dome C (see Figure 4) by the French and Italian 2 This work featured in the Astrophysical Journal in 2000 in an article entitled 'High resolution imaging of photodissociation regions in NGC 6334' by Burton, M.G., Ashley, M.C.B., Marks, R.D., Schinckel, A.E., Storey, J.W.V., Fowler, A., Merrill, M., Sharp, N., Gatley, I., Harper, A., Loewenstein, R., Mrozek, F., Jackson, J. & Kraemer, K. vol 542, pages

3 Antarctic programs. One of the principal experiments was to measure the quality of the astronomical seeing or the twinkling of the stars, for we had reason to believe that the extreme stability of the atmosphere above would lead to corresponding clarity in the image quality. This was subsequently verified through an experiment that ran completely unattended through the Antarctic winter, communicating its results through the Iridium phone network. 3 Since then work has continued to further characterise the Antarctic plateau as a site for astronomy, and to find the very best place for an observatory to be built. Two particular ventures are now underway as part of Australia s contributions to the International Polar Year (IPY) of The first is an engineering study for a 2.4m-sized telescope (PILOT, the Pathfinder for an International Large Optical Telescope), supported by the Australian-government (see Figure 5.). This telescope would be built at Dome C if funded, through a collaboration between Australian and European scientists. It is a large enough telescope that it could undertake significant new science in its own right, and yet at the same time it is relatively modest in size compared to some telescopes being planned elsewhere, and so can be built for far less cost. It also paves the way for future grand-design telescopes, the ultimate telescopes that may be built from the very best sites on Earth. The second venture is to the very summit of the Antarctic plateau, possibly the best site on our planet for astronomy. This site was first visited in 2005 by a Chinese expedition. It is the 4,200m Dome A, also within the Australian Antarctic Territory. A new site testing observatory, PLATO (PLATeau Observatory) was also built in Australia, and shipped to Antarctica from Fremantle with the Chinese in It has now arrived at Dome A, where it is being integrated with Chinese experiments (see Figure 6), and will begin making the first measurements of the astronomical conditions their during the winter of China now plans to build a new station at Dome A over the next three years. 3 This was reported in the journal Nature in an article entitled, 'Exceptional astronomical seeing conditions above Dome C in Antarctica', written in 2004 by Lawrence, J.S., Ashley, M.C.B., Tokovinin, A. & Travouillon, T. vol 431, pages

4 Figure 1. The Infrared Spectrometer Photometer (IRPS) at the South Pole in January 1994, Australia s first Antarctic astronomy experiment. Image Michael Burton.

5 Figure 2. SPIREX, the South Pole Infrared Explorer, the first infrared telescope in Antarctica, at the South Pole in Image Michael Ashley.

6 Figure 3. An infrared image of a galactic stellar nursery taken by the SPIREX telescope. The blue colour shows the infrared emission from organic molecules (polyaromatic hydrocarbons) at 3.3 m. Image Michael Burton.

7 Figure 4. The French-Italian Concordia station at Dome C in 2003, with the Australian AASTINO laboratory (Automated Astrophysical Site Testing Observatory) to foreground. Image John Storey.

8 Figure 5. Design for the 2.4m PILOT telescope at Dome C, the Pathfinder for an International Large Optical Telescope. Image Andrew McGrath.

9 Figure 6. The PLATO laboratory at Dome A, January 2008 with the Chinese CSTAR experiment to foreground. Image Polar Research Institute of China.