[Cmunipack] Photometry

[cmunipack , amper.ped.muni.cz]

Hi Jorg and Marek,

Jorg, could you sent me please the FITS file of the U Gem field, which 
was not processed correctly? Please, send me the file after all 
corrections (or at least dark and flat frame too) and also your ini 
files if they differ from the ones you sent me last week. Now I have no 
proper debug outputs in the photometry so I have to check it in on my PC...

Ad sigmas:
Sigma means standard deviation. In this case it is standard deviation of 
the image background. In the photometry routine, before the photometry 
is started, the program measures the mean value and noise level of the 
sky. So when the threshold is set to 3.0 sigmas, it means that the value 
of the pixel which is in the center of the star must be equal to or 
greater than mean background level plus three time the noise level.

"Cut off"s are also used for star filtering. The roundness and sharpness 
are statistical moments (I can send you exact mathematic formulas, but 
they are awful.) High xxx cutoff means, that the value of the parameter 
xxx must be equal to or less that the cutoff. Low cutoff is same for 
lower limit.

I do apologize, all this stuff should be in the documentation and I hope 
it will be some day...

Best wishes,

David


cmunipack , amper.ped.muni.cz napsal(a):
> Hi Marek,
> 
> thank you for this hint. I changed the threshold gradually from 5 down 
> to 3 sigmas. More "stars" are detected (I think there aren't 200 stars 
> in the picture) but the problem is still the same.
> By the way I have a question about these sigmas. Low good datum is in 
> sigmas and threshold is in sigmas. But sigmas of what? Can I compute the 
> appropriate value of sigma for my set of frames?
> Another thing that I don't understand are the four " .....cut off". What 
> does the values mean? I couldn't find an explanation in the helpfile.
> Thank you for your help.
> 
> Best regards
>    Jörg!
> 
> 
> ----- Original Message ----- From: <cmunipack , amper.ped.muni.cz>
> To: <cmunipack , amper.ped.muni.cz>
> Sent: Friday, May 11, 2007 3:32 PM
> Subject: Re: [Cmunipack] Photometry
> 
> 
> Hi Jorg,
> 
> maybe you have set up too high Threshold.
> 
> Best regards
> Marek!
> 
> Citát cmunipack , amper.ped.muni.cz:
> 
>> Hallo David and you all,
>>
>> when I examened the srt-files of the U Gem field I found out that even 
>> bright stars (1500 ADU out of 4096 ADU) were missing on a lot of 
>> frames although there weren't any bad pixels in them. I had a close 
>> look at these frames but I can't see any pattern behind this behavior 
>> of the program.
>>
>> Best regards
>>    Jörg!
>>
>>
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> 
> 
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