Periodic error
Andras Dan send me a new worm (or mother screw) which he has tested to the sky to fix the periodic error. An this is what I was able to measure afterward :
The error remains within +/- 2 arcsec over 600sec, the RMS error is 0.88 arcsec. The pixel size is 3.16 arcsec in binning 1x1. It looks better now ! Also the automatic pointing of the telescope is OK, I've always have the object centered into the field.
Images
Since I'm surrounded by 5 high powerful street light, it is really tough to undertake deep sky imaging in such conditions. I've tried to record the M101 field, making 10 images of 60sec.
Raw
image of M101, 60sec binned 2x2. In that condition and without Moon, I've
got a background ranging from 8500 ADUs (Max is 16383) to the zenith to 12000
ADUs at 30° to west, 60sec exposure, 2x2 binning. That's like I was observing
in twilight or at a couple of degrees from the Moon (!). The images are extremely
difficult to flat field out properly.
Nevertheless, after combining and processing 10 images (PRiSM v4), this is what I got :
10
times 60sec combined image of M101. Note that some remainder of flat field
are still contaminating the image....Note also the large field of view!
To be more accurate concerning the light disturbance, we have computed the limiting magnitude and it yield to this histogram (PRiSMv4):
X is the magnitude and Y the amount of stars in the image, it shows that the limiting magnitude is about 17.2, the same calculation on a single image from the 10 yields to 16.2. By adding 10 images we gain one magnitude.
Above another interesting plot showing the signal to noise ration versus magnitude. All stars are inside the main part of this plot, the rest are galaxies, or non-stellar objects.
SN corner
One of the goal of this system is to detect SNs, so let's see how it behaves with real life ! We try with SN 2000CN in PGC61173 (UGC11064). Also additionnal information about AUDE SN network can be found here, and international network there, and VSNET. I used the text file written by JmL.Llappasset that can be downloaded by PRiSM to display the SNs to measure.
Field of 2000CN, a SN very close to the galaxy center (PRiSMv4).
Here can be found the full 1x1K field(50'x50') recorded, binning 1x1. A close up does show barely the SN where it supposed to be. But I can't measure it, must be around the 16.5th magnitude. The discovery image can be found here.
The
arrow shows the SN, but this is hardly visible !!
Conclusions
Obviously, this is hopeless to keep on observing in my home's garden unless I find a way to switch off these bloody street lights...
Home garden... too much light going thru it overnight.
According to my measurement I got magnitude 15 with 1700 ADUs of signal, this would mean that I could have magnitude 19 with 52 Adus, knowing that the sky background is around 10000 Adus (i.e. 48000e-), I've got a background photon noise of 45 Adus which is almost equal to the signal of a star of magnitude 19...That's why...
Now, I will have to seek for another place for that telescope... Observers must emigrate or die !!