Australia Telescope National Facility

Infrared and Sub-millimetre Observing Conditions on the Antarctic Plateau

Marton G. Hidas, Michael G. Burton, Matthew A. Chamberlain, John W.V. Storey, PASA, 17 (3), 260.

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Introduction

It is now well established that the Antarctic plateau can provide the best terrestrial astronomical observing conditions across the infrared and sub-millimetre wavebands (eg. Nguyen et al. 1996, Ashley et al. 1996, Chamberlin et al. 1997, Phillips et al. 1999, Chamberlain et al. 2000, Ade et al. 2000). It is well understood that this is a result of the extremely dry and cold air, and the high elevation of the plateau (over 3000m). As an example, at the South Pole in winter temperatures fall below $-70^{\circ}$ C and the precipitable water vapour in the atmosphere below 250 $\mu$ m. This leads to extremely dark skies, as summarised in Burton 1998. At 2.4 $\mu$ m the sky brightness can fall below 100 $\mu$ Jyarcsecond^-2 (20-100 times less than at temperate sites), at 3.6 $\mu$ m to $\sim 100$ mJyarcsecond^-2 ( $\sim 20$ times less than at temperate sites), at 11 $\mu$ m to $\sim 20$ Jyarcsecond^-2 ( $\sim 10$ times lower), and at 350 $\mu$ m to $\sim 60$ Jyarcsecond^-2 (a reduction of two). At the highest points of the plateau, such as Domes A and C, conditions are expected to be even more favourable, due to further reductions in temperature and water vapour content. These sites also offer improved seeing due to lower wind speeds and a thinner inversion layer.

The improvements in the infrared and sub-millimetre observing conditions compared to temperate sites are surmised to arise from three principal effects: low temperature, low water vapour content and low levels of particulates. The low temperature results in a reduction of the background sky emission. The low water vapour improves the atmospheric transmission and correspondingly decreases its emissivity. The reduced particulate content of the atmosphere also reduces its emissivity compared to a mid-latitude site. However these effects, while they are interelated, vary significantly with wavelength. In this paper we apply an atmospheric modelling program to compare their contributions and thus quantify their effects.

Next Section: MODTRAN Modelling
Title/Abstract Page: Infrared and Sub-millimetre Observing
Previous Section: Infrared and Sub-millimetre Observing
Contents Page: Volume 17, Number 3

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