We present the Gattini project: a multisite campaign to measure the optical sky properties above the two high altitude
Antarctic astronomical sites of Dome C and Dome A. The Gattini-DomeC project, part of the IRAIT site testing
campaign and ongoing since January 2006, consists of two cameras for the measurement of optical sky brightness, large
area cloud cover and auroral detection above the DomeC site, home of the French-Italian Concordia station. The cameras
are transit in nature and are virtually identical except for the nature of the lenses. The cameras have operated
successfully throughout the past two Antarctic winter seasons and here we present the first results obtained from the
returned 2006 dataset. The Gattini-DomeA project will place a similar site testing facility at the highest point on the
Antarctic plateau, Dome A, with observations commencing in 2008. The project forms a small part of a much larger
venture coordinated by the Polar Research Institute of China as part of the International Polar Year whereby an
automated site testing facility called PLATO will be traversed into the DomeA site. The status of this exciting and
ambitious project with regards to the Gattini-DomeA cameras will be presented.
The Gattini cameras are two site testing instruments for the measurement of optical sky brightness, large area cloud cover and auroral detection of the night sky above the high altitude Dome C site in Antarctica. The cameras have been in operation since January 2006. The cameras are transit in nature and are virtually identical, both adopting Apogee Alta ccd detectors. The camera called Gattini-SBC images a 6 degree field centred on the South Pole, an elevation of 75° at the Dome C site. The camera takes repeated images of the same 6 degree field in the Sloan g' band (centred on 477nm) and, by adopting a lens with sufficiently long focal length, one can integrate the sky background photons and directly compare to the equivalent values of the stars within the field. The second camera, called Gattini-allsky, incorporates a fish-eye lens and images ~110 degree field centred on local zenith. By taking frequent images of the night sky we will obtain long term cloud cover statistics, measure the sky background intensity as a function of solar and lunar altitude and phase and directly measure the spatial extent of bright aurora if present and when they occur. An overview of the project is presented together with preliminary results from data taken since operation of the cameras in January 2006.
Profiling the ground layer turbulence for daytime seeing applications using an array of photodiodes has been documented
in literature, in particular by Beckers who coined the term "SHABAR" for the instrument, short for Shadow Band
Ranger. In this case the photodiodes measure the variation of solar intensity as a function of time and the correlation of
scintillation between spatially separated scintillometers can be used to derive structure constant values for the lower
100m or so. More recently SHABARs have been applied to night time atmospheric profiling using the moon as the
extended source, such as the Pan-STARRS lunar SHABAR, a more challenging venture given the lower structure
constant values and therefore higher sensitivity required. We present a summary of the lunar SHABAR currently
operating at the Antarctic site of Dome C, one of the three Gattini site testing instruments for the Italian-led IRAIT
project. The SHABAR was designed with low noise performance in mind and for low temperature operation. Ground
layer profiling is of particular importance at the Dome C site during winter-time as it is known the majority of the
integrated seeing measured at ground level is created in a turbulent layer very close to the ground.
Recent data have shown that Dome C, on the Antarctic plateau, is an exceptional site for astronomy, with atmospheric
conditions superior to those at any existing mid-latitude site. Dome C, however, may not be the best site on the
Antarctic plateau for every kind of astronomy. The highest point of the plateau is Dome A, some 800 m higher than
Dome C. It should experience colder atmospheric temperatures, lower wind speeds, and a turbulent boundary layer that
is confined closer to the ground. The Dome A site was first visited in January 2005 via an overland traverse, conducted
by the Polar Research Institute of China. The PRIC plans to return to the site to establish a permanently manned station
within the next decade. The University of New South Wales, in collaboration with a number of international institutions,
is currently developing a remote automated site testing observatory for deployment to Dome A in the 2007/8 austral
summer as part of the International Polar Year. This self-powered observatory will be equipped with a suite of site
testing instruments measuring turbulence, optical and infrared sky background, and sub-millimetre transparency. We
present here a discussion of the objectives of the site testing campaign and the planned configuration of the observatory.
The brightness of the night sky at an astronomical site is one of the principal factors that determine the quality
of available optical observing time. At any site the optical night sky is always brightened with airglow, zodiacal
light, integrated starlight, diffuse Galactic light and extra-galactic light. Further brightening can be caused
by scattered sunlight, aurorae, moonlight and artificial sources. Dome C exhibits many characteristics that
are extremely favourable to optical and IR astronomy; however, at this stage few measurements have been
made of the brightness of the optical night sky. Nigel is a fibre-fed UV/visible grating spectrograph with a
thermoelectrically cooled 256 × 1024 pixel CCD camera, and is designed to measure the twilight and night sky
brightness at Dome C from 250 nm to 900 nm. We present details of the design, calibration and installation of
Nigel in the AASTINO laboratory at Dome C, together with a summary of the known properties of the Dome C
sky.
To properly characterize the atmospheric properties of a site for a future large telescope or interferometer, it is insufficient to measure quantities, such as the full-width at half-maximum of a stellar image, that have been integrated over the entire atmosphere. A knowledge of the turbulence distribution as a function of height is necessary, since this affects the ease and degree to which adaptive optics systems can improve the telescope’s resolution. Furthermore, some astronomical measurements, such as narrow-field differential astrometry at microarcsecond precision, depend critically on the amount of turbulence high in the atmosphere (up to 20km). In order to obtain the necessary site-testing data at remote sites such as those on the Antarctic plateau, we have designed a robust and reliable instrument based on an 85 mm refractive telescope, a gimbal-mounted sidereostat mirror, and a Multi-Aperture Scintillation Sensor (MASS). The instrument uses the spatial structure of single-star scintillation to measure vertical turbulence profiles from 0.5 to 20km. The MASS system is designed to operate completely autonomously throughout the Antarctic winter. It also has potential applications at existing observatory sites for quantifying the turbulence characteristics of the atmosphere in real-time.
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