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The Lunar Scintillometer
Paul Hickson & Arlin Crotts
Seeing tests have begun for the 8-meter
ALPACA telescope (Advanced
Liquid-mirror Probe of Astrophysics, Cosmology and Asteroids) with the
installation of a microthermal array and a lunar scintillometer designed to
locate the height of turbulence producing the seeing above the site on the
northern lip of the Cerro Tololo summit.
The instrument in the picture is the lunar scintillometer and consists of an
array of photodiodes that will measure the light coming from the Moon, which
is bright enough so that the correlations between photodiode channels allow
one to dissect how atmospheric turbulence is divided up among the regions of
overlap between the cones viewed by the photodiodes. Measurements also include
data from four microthermal sensors intalled on a 30m tower, which will
provide additional information on turbulence near the ground.
The lunar scintillometer monitors a region overlapping the tower and extending
roughly 1 km over the site.
These measurements are preparations to install
ALPACA, expected to begin
observations in 2010, and which will be a low-cost imaging survey
instrument to explore the band of sky passing through the zenith at Cerro Tololo.
Since ALPACA will only point straight up, it will be housed in a
surprisingly small building aerodynamically designed to minimize the impact
on seeing in the surrounding buildings.
The survey will continue for several years and may be expanded with additional
instrumentation.
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