9/29 - Obs Belle Etoile

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Olivier Thizy
Posts: 370
Joined: Sat Sep 24, 2011 10:52 am
Location: in the french Alps...
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9/29 - Obs Belle Etoile

Post by Olivier Thizy »

Hello,


I have observed QR Vul, P Cyg, 28 Cyg, 32 Cyg, 31 Cyg so far. I am on HD195407 now...

For bright objects, I was taking too many exposures. I have used the following method to calculate the right number of exposure to take - I'll document it later with several screen shots but in a nutshell:
-Take one short exposure (10s) to see the maximum & minimum ADU level where the spectrum is the brightest
-I am shooting for a max ADU around 40000 so my exposure time would be:
Exposure Time in seconds = 400000/(max-min)
-After two exposures, I reduce each of them individually
-I divide the first profile with the second, I obtain a rather flat signal but noisy
-In ISIS I measure the SNR around Halpha (in my case, I just measure the 34th order)
-I calculate the number of exposure to reach a Signal/Noise Ratio of 100 (rounded to the integer above):
Nb Exposures = ((100/SNR)/1.4)^2

This seems to work fariyl well as I measure a SNR just above 100 for the targets I have used this method so far on.


Clear skies to all,
Olivier Thizy
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