VLT-MAN-ESO-14650-4942
P96
24.06.2015
87 of 161
ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
Figure 2bis: A&G CCD quantum efficiency
curve.
The A&G CCD cooling system produces small oscillations of the CCD temperature.
Temperature variations affect the dark current level. In case of short exposure times, when
the image sampling frequency corresponds to the frequency of the temperature oscillations,
this leads to “beats” and background level variations from one image to the next. These
variations in background level disappear if a longer exposure time is selected. However, they
do not affect the acquisition performance. In June 2011, the noise was improved and the
quality of images now allows detecting objects as faint as magnitudes 25 in R and V bands in
3 min exposures and good weather conditions.
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