Report - School of Physics

een produced, diffraction effects caused by scintillation may dominate in the far
wings and halos of the image. Scintillation, originating in inhomogeneities of the
higher atmosphere, causes patterns of ‘flying shadows’ on the ground (with intensity
contrasts of perhaps only a few percent), carried across the telescope pupil at the
windspeed of the originating atmospheric layer. In principle, this could be corrected
by second-order adaptive optics (modulating both the phase and amplitude), but the
task is not trivial. An additional advantage for Dome C (assuming that ‘ordinary’
adaptive optics will be fully operational) is that such sites also appear to have very
much less scintillation: not only do the low windspeeds (no jet streams such as
prevail over Chile and Hawaii) imply much less energy deposited in atmospheric
turbulence, but the winter-time atmospheric structure is such that the tropopause
effectively reaches the ground, with no significant temperature discontinuities in the
higher atmosphere.
In the most favourable cases (K band and an L band extended to 2.8–4.2 µm)
Dome C thus provides a near space-quality environment, presumably at a small
fraction of the cost, and with almost no limitations in weight or volume. The
logistics for the station were developed by the French (IPEV) and Italian (PNRA)
polar institutes: humans reach the site by plane with a total travel time of about
48 hr from Europe, while the heavy equipment is shipped in standard containers
by boat to the coast and then by pack trains of Caterpillar trucks onto the glacier
slopes up to Concordia.
It is still the accepted wisdom that a census of exo-Earths and the characterisation
of their atmosphere (in search for biomarkers) will require a space mission such as
Darwin. The survey part of the Darwin programme could perhaps be undertaken
from Dome C, given the extreme phase and background stability of the site. A
preliminary study should be undertaken to determine whether this could be achieved,
either with a coronographic ELT in the visible or near-IR, or a large interferometer in
the thermal infrared. This would enable Darwin to concentrate on the spectroscopy
of identified targets, i.e. at wavelengths 6–18 µm where clear biomarkers exist and
which for the most part are not accessible from Dome C. A simplified interferometer
(two 1 m telescopes) equipped with a GENIE-type instrument could provide goodquality
spectra of hot (Jupiter- or Neptune-class) bodies and the characterisation of
exo-zodiacal light around main-sequence nearby stars – precursor science for Darwin
that otherwise necessitates extensive use of VLT UT time. Other applications of
Dome C for exo-planets include astrometry and transit photometry. The ultimate
astrometric accuracy of an interferometer was estimated by Swain et al. (2003) to be
a factor of some 30 better at Dome C than at Paranal. However, before this potential
gain is realised, the technique must have matured to the point where astrometry on
temperate sites is limited by the atmosphere only, and not by systematic effects.
Transit photometry could benefit from lower scintillation, and longer continuous
time coverage (polar night), than on temperate sites.
The nature of the site, halfway between ground and space, makes it an especially
interesting area for collaboration between ESO and ESA. Although Europe is natu-
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