Frame transfer -> FOV 4.3deg 2 16 readout amplifiers Slow:
40s; fast 2.5s
Slide 5
To check the overall performance Fridge: producing different
environment temperatures down to 80C Light source: a LED lighting
through several layers of white paper 2 CCD test results
Slide 6
Linearity Signal level.vs. Exposure time Full well capacity
> 100,000 e
Slide 7
Photon Transfer Curve (PTC) gain: e- -> analog-to-digital
units (ADU) pairs of flat frames with various signal levels
Variance: photon shot noise + readout noise 2 = N/g + 2 rd /g 2 1/g
is the slope of the variance-signal plot g ~ 1.64 e-/ADU
Slide 8
Readout Noise RMS of the overscan Slow: 4 e-; fast: 9-12 e- sky
brightness (AST3-1 in 2012) 8e-/sec for 60sec exposure, photon shot
noise 22 e- Fast mode is used for observation
Slide 9
Dark Current thermal electrons decreases by half as the
temperature is lowered every 7.3C
Slide 10
Charge Transfer Eciency CTE: the fraction of charges
transferred from one pixel to the next during readout Extended
Pixel Edge Response (EPER): excess charges found in the
overscan
Slide 11
3 Nonlinear PTC Downing+06 reported this effect, and found it
was caused by signal correlation between pixels Downing &
Sinclaire (2013): charge diffusion due to the Coulomb force of
stored charges (charge sharing) Antilogus+ 14: effective pixel
boundaries shift; predicting brighter-fatter effect from PTC
Downing & Sinclaire (2013)
Slide 12
We proposed a simple model, named charge sharing PSF, assuming
charge sharing fraction as a function of signal level AST3 CCDs
show significant signal correlation between a pixel and its
neighbors: (0,1)(0, 2)(1,1) Deriving charge sharing PSF from PTC,
then estimating the effect on real image
Slide 13
Profiles of stars (FWHM, elongation) depend on their
brightness, biasing photometry and shape measurement.
Slide 14
4 Current status CCD#1 (engineering grade) on AST3#1 in 2012 In
Jan 2015, 31th Chinese Antarctic Research Expedition (CHINARE) team
deployed AST3#2 with CCD#2, and replaced CCD#1 with CCD#3 Realtime
status is shown on website
http://aag.bao.ac.cn/ast3-2/index.php
Slide 15
Slide 16
CCD temperature control Original TEC control makes t_CCD
oscillate around setpoint with a amplitude of 4 degrees Prof.
Ashley has done a great job to keep it much more stable (~0.2
degree) 2015.02.11 2015.02.16
Slide 17
The heat from CCD chip by TEC is not removed efficiently, so
TEC cannot cool CCD very much T_CCD is about 10 degrees above
ambient temperature Dark current level@-50C: 1.7e-/sec (CCD#1),
0.29e-/sec(CCD#2) sky brightness (AST3-1 in 2012) 8e-/sec Noise
from dark current is expected to be insignificant
