PHOT/Msky

laure wrote on Nov 17, 2010

Hi,

I'm comparing two photometry procedure, IRAF/PHOT and Funtools and I get very different results whereas comparing the two methods with non background-substracted counts, I obtain very consistant results.

I can conclude that the problem comes from the background estimation.

Does anybody know how Msky is determined please?

Thank you very much!

Laure

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Mike Fitzpatrick wrote on Nov 17, 2010

The Msky value is actually just an average of the values calculated for the sky region, however there are several methods by which you can fit the sky region. The help page for the FITSKY task and FITSKYPARS pset has some information, more detailed information on each algorithm can be found in the specification for the APPHOT package (http://iraf.net/irafdocs/apspec/). Note also that the psets used to specify the data parameters (e.g. gain, readnoise, etc in the DATAPARS) also play a part in the fit and may be set inappropriately.

I don't know how the funtools code works so I can't draw a direct comparison. Hope this helps.

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laure wrote on Nov 17, 2010

thank you very much!

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laure wrote on Nov 17, 2010

Hello,

I have still a last question about PHOT:
I've set the k-sigma clipping (low and high) to 100 in order to prevent PHOT from excluding pixels in the background.

But it seems that PHOT still rejects pixels that could correspond to sources in the background...

Am I wrong? is there another parameter to set?

Thank you very much!

Laure

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Last post on Nov 17, 2010