Initial Investigations

Whilst the camera was cooling we attempted to take light frames (pointed at a roughly uniform section of the inside of the dome) in order to see the receeding cooling ring, which we could not see previously as we cooled too much. Initial readings were unsuccessful during initial cooling phase, as saturations were quickly met and not enough data was collected. Future investigations will be conducted to better understand the phenomena of the expanding cooling ring and whether or not this is an affect we need to be wary of.

Next we investigated the so called bias level in ADU, needed for working out an accurate number for the amount of photon events compared to the number of ADU's outputted by the CCD. This was achieved by taking five zero second exposure dark frames, which will then be averaged over their arrays, and between each image to find the bias.

In addendum to dark frames taken previously, It was questioned whether or not the 'hot' pixels appearing in longer exposures were a fault of the camera, and appeared in the same places, or whether this was due to other effects. Looking into the dark frames, it was seen that the 'hot' pixels appeared to be randomly distributed over the images for several exposures, appearing both as 'dots' and as 'streaks'. Therefore we conclude that these must be from a foreign influence, not from the CCD or optics of the system. Examples of these can be seen below.


Additionally, looking at higher exposure times, there appears to be an increase in the amount of 'dots' and 'streaks', however as of yet this has not yet been thoroughly tested. If this is indeed the case, then this would be consistent with a flux of incident particles decaying at a constant rate, and could be explained by naturally occuring cosmic rays. Upon taking an hour long exposure (significantly longer than previous max of 300 seconds), only very few of these effects were seen, converse to the trend seen for lower exposures. A possible reason could be that over such an exposure, the 'hot' pixels are masked as the backgrond around them is increased, making them less visible, so the chance of seeing any easily detectable events is reduced.

These 'cosmic ray tests' were first done with the camera placed in the back of the telescope, at around 45 degrees from the horizontal. Cosmic rays are generally expected to fall directly downards, so if the camera was facing upwards, then cosmic rays would register on the CCD as a bright dots, whereas if at an angle, these could register as streaks. For the data taken for an upwards facing camera [no] streaks were seen, but as seen before, some streaks can be seen for the angled position. Therefore these may well be due to cosmic rays, or decay related radiation produced in the atmosphere. Below is seen a comparison of two hour long exposures, one at an angle, and one facing upwards:

-side by side, streaks, no streaks, up or angle-



-- DavidHadden - 27 Oct 2015

Topic attachments
I Attachment Action Size Date Who Comment
PNGpng 120s.png manage 452.9 K 27 Oct 2015 - 16:43 DavidHadden  
Compressed Zip archivezip manage 4832.6 K 27 Oct 2015 - 13:59 DavidHadden  
Compressed Zip archivezip manage 10184.2 K 27 Oct 2015 - 13:59 DavidHadden  
PNGpng hour_comparison_correct.png manage 197.2 K 27 Oct 2015 - 16:04 DavidHadden  
PNGpng hour_comparison_zoom_correct.png manage 241.3 K 27 Oct 2015 - 16:11 DavidHadden  
Compressed Zip archivezip manage 5875.8 K 27 Oct 2015 - 11:16 DavidHadden  
Edit | Attach | Print version | History: r7 < r6 < r5 < r4 < r3 | Backlinks | Raw View | Raw edit | More topic actions...

Physics WebpagesRHUL WebpagesCampus Connect • Royal Holloway, University of London, Egham, Surrey TW20 0EX; Tel/Fax +44 (0)1784 434455/437520

Topic revision: r6 - 27 Oct 2015 - ElenaCukanovaite

This site is powered by the TWiki collaboration platformCopyright © 2008-2018 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding RHUL Physics Department TWiki? Send feedback