Temperature Control for CCD

We first tested the lowest temperature we could achieve for the CCD, whilst keeping the cooler power at around 90%, so that small changes in atmospheric conditions could be accounted for by the cooler, so the temperature of the camera could remain as fixed as possible.

Ambient Temperature today: 12 degrees celsius, and tested in the range -10 to -20 degrees, the results of which can be seen in the table below:

Temperature (Degrees Celsius) Cooler Power (%)
-9.8 to -10.2 62 to 65
-14.8 to -15.2 75 to 80
-16.9 to -17.4 87 to 91
-20.0 100

From this we concluded that the optimum temperature for today's observations is around -17 degrees, and was used throughout.

Thermal Noise

We then set about determining the thermal noise created by the system. For this the lens cap was left on, as we were only interested in seeing what images where produced due to thermal noise, not from outside sources. We took images at different exposure times, as seen in the attached zipped file (Exposure_test_lens_cover_on.zip), containing the FITs files. A 200 second exposure can be seen annotated below.

DarkFrameCropAnnotated.png

Here A is most likely a 'hot' pixel, around 4 magnitudes brighter than the background of the image. B is another bright spot, but this time more spread out, and around 2 magnitudes brighter than the background. The interesting feature at C was first thought to be a cosmic ray, as it appears to have moved over the image during exposure, however it appears to have curved in a noticable way, over a small distance, perhaps identifying it as a low momentum, charged particle. We have yet to acertain whether this is a result of natural radioactivity however.

CCD Faults (?)

Then we removed the lens cover and took images of a smooth side of the inside of the dome, and from this we identified two interesting properties of the camera. First several ring structures are visible in such conditions, marring the observed image. These can be identified as dust on the optical components of the telescope, resulting in 3 distinct ring sizes, correpsonding to dust on one of the 3 components. A annotated picture showing these and related parameters can be seen below. Below saturation an overbright cirular line is visible on the images, this is identified as due to the cooling ring which cools down the CCD chip, which shows a sharp cut-off section around the edge of the image, uncharacteristic of any affect caused by the optics. However when saturation is reached (~40 seconds), the image is warped considerably, and this line is no longer present. The full set of files can be seen in the zipped file titled Exposure_test_lens_cover_off.zip

LightFrameAnnotatedpng.png

Here A shows the largest of the rings, with an outer ring diameter of around 340 pixels, and an inner ring diameter of 130. B is the medium ring, with outer and inner ring diameters of 180 and 75 pixels respectively. Seen very faintly at C is one of the small rings, which due to its size, only one ring can be measured for, at around 12 pixels. D hghlights the cooling ring of the camera, which although much brighter looking, has around 1000-1500 additional ADU's.

Analysis

The thermal noise image for 0.1 seconds was used for the following analysis. The pixels values were divided in to 50, 100, 300 bins as can be seen below.

thermal_noise_0_1s_50_bins.png

thermal_noise_0_1s_100_bins.png

thermal_noise_0_1s_500_bins.png

For longer exposure times there were very bright collections of pixels that could be cosmic rays. This made it harder to plot a histogram since the pixel values for these unusual pixels were about 100 times bigger, so these pixels were removed by defining that anything above 600 ADU is to be removed. 32 of such pixels were removed. 1560568 pixels were left. The image below shows the histogram for 50s exposure time:

thermal_noise_50s_500_bins.png

-- Public.DavidHadden - 13 Oct 2015

Topic attachments
I Attachment Action Size Date Who Comment
PNGpng 10scoffAnnotated.png manage 1449.0 K 20 Oct 2015 - 15:34 DavidHadden  
PNGpng DarkFrameCropAnnotated.png manage 357.1 K 21 Oct 2015 - 13:32 DavidHadden  
Compressed Zip archivezip Exposure_test_lens_cover_off.zip manage 17595.8 K 13 Oct 2015 - 15:15 DavidHadden Exposures of the side of the dome, taken with the lens cover removed.
Compressed Zip archivezip Exposure_test_lens_cover_on.zip manage 14439.3 K 13 Oct 2015 - 14:42 DavidHadden Exposure time test with the lens cover on.
PDFpdf LightFrameAnnotatedpdf.pdf manage 1434.7 K 21 Oct 2015 - 13:19 DavidHadden  
PNGpng LightFrameAnnotatedpng.png manage 1623.2 K 21 Oct 2015 - 13:26 DavidHadden  
PNGpng histogram.png manage 35.2 K 13 Oct 2015 - 19:57 ElenaCukanovaite Histogram for one of the thermal noise images.
PNGpng thermal_noise_0_1s_100_bins.png manage 29.4 K 16 Oct 2015 - 21:07 ElenaCukanovaite Thermal noise image for 0.1s with the pixel values divided in to 100 bins.
PNGpng thermal_noise_0_1s_500_bins.png manage 29.0 K 16 Oct 2015 - 21:07 ElenaCukanovaite Thermal noise image for 0.1s with the pixel values divided in to 500 bins.
PNGpng thermal_noise_0_1s_50_bins.png manage 26.3 K 16 Oct 2015 - 21:07 ElenaCukanovaite  
PNGpng thermal_noise_50s_500_bins.png manage 29.4 K 17 Oct 2015 - 20:05 ElenaCukanovaite  

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Topic revision: r8 - 21 Oct 2015 - DavidHadden

 
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