I made some quck calculations based on sky images from 20180115 (for sky images) and 20180116 (for high S/N bias and dark images).
This work from: /home/sco/Study1/S/README.Study1
Here I do a quick analysis of the bias and dark images from 20180106
and also some sky images from 20180105.
Image Num_images Mean sigma m.e. Npix
bias1 28 1389.8395 15.8844 0.0457 121022
bias2 42 1388.5105 15.7676 0.0413 145590
bias3 70 1388.7037 16.8659 0.0397 180799
bias4 105 1391.0508 15.5541 0.0576 72969
Mean bias = 1389.5 -+0.6
Bias-subtracted
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dark_5sec 28 1392.3094 16.8975 0.0637 70352 2.9 adu 0.56 adu/sec
dark_10sec 28 1393.2416 28.8734 0.1001 83188 3.7 adu 0.37 adu/sec
dark_20sec 28 1395.1547 47.3694 0.1541 94487 5.6 adu 0.28 adu/sec
sky_g 1 1440.2162 26.6864 0.1927 19172
sky_r 1 1577.8711 31.2581 0.1864 28134
NOTE: Mean bias for 20180115 = 1382.9 -+0.4
For the 5 sec images:
dark = 1392.3 - 1389.5 = 2.8 adu
skyg = 1440.2 - 1382.9 - 2.8 = 54,5 adu 11.0 % error
skyr = 1577.8 - 1382.9 - 2.8 = 192.1 adu 3.1 % error
Suppose I have no bias frame (or dark)? This means roughly my sky levels
are uncertain by -+6adu (just a guess). The resulting percentage errors
are shown above for the g,r sky images
20180116T034431.2_acm_sci.fits = a single bias image (from the bias1 set).
20180116T041113.8_acm_sci.fits == single 5sec dark
For sky images I had to use the previous nighT
20180115: clear, dark night (no moon)
Using the images in /home/mcs/astronomer/sco/RA_logs/20180115/lmrun:
[astronomer@mcs lmrun]$ pwd
/home/mcs/astronomer/sco/RA_logs/20180115/lmrun
[astronomer@mcs lmrun]$ gethead 20*fits OBJECT FILTER EXPTIME
Here I record only the 5sec images
20180115T051213.9_acm_sci.fits ___ g` 5
20180115T055730.5_acm_sci.fits ___ r` 5
20180115T084419.9_acm_sci.fits ___ r` 5
20180115T092450.5_acm_sci.fits ___ r` 5
20180115T100140.3_acm_sci.fits ___ g` 5
20180115T110644.2_acm_sci.fits ___ r` 5
20180115T114129.5_acm_sci.fits ___ r` 5
20180115T121920.4_acm_sci.fits ___ r` 5
Note: I did take a 25 image bias set on 20180115, here are the stats:
1390.4210 0.1131 73.5987 25 20180115T042224.8_acm_sci
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Here I subtract bias and dark:
To make a bias-subtracted dark5:
clip_imarith.sh dark_5sec.fits - bias4.fits dark5.fits
Mean = 1.5 adu (0.3 adu/sec)
The g sky image:
clip_imarith.sh sky_g.fits - bias4.fits im1.fits
clip_imarith.sh im1.fits - dark5.fits im2.fits Signal = 46.5 adu 9.30 adu/sec
The r sky image:
clip_imarith.sh sky_r.fits - bias4.fits im1.fits
clip_imarith.sh im1.fits - dark5.fits im2.fits Signal = 182.3 adu 36.45 adu/sec