AST3 detector properties Ma Bin (NAOC) 2015.03.09 2015 AST3 meeting@HKU
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- Slide 1
- AST3 detector properties Ma Bin (NAOC) 2015.03.09 2015 AST3
meeting@HKU
- Slide 2
- OUTLINE 1 AST3 CCD 2 CCD test results 3 Nonlinear PTC 4 Current
status
- Slide 3
- 1 AST3 CCD STA 1600FT 10560 * 10560 pixels Pixel size 9m ->
1 thermoelectric cooling (TEC)
- Slide 4
- 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
- Slide 18
- Thank you !