Hi,
I'm using the IDL routine 'Aper' which is derived from the DAOPHOT aperture
photometry routine and am trying to understand why it calculates errors the
way it does. The error the routine derives is given by:
error=sqrt((photon noise)^2 + (num_pix_aperture*sigma(sky)^2) +
((num_pix_aperture^2)*(sigma(sky)^2)/num_pix_sky))
I understand that the photon noise and the error in the sky value applied
within the aperture are important but I'm unsure why there is an extra term.
Does anyone know any documentation which explains the reasoning behind this?
Many Thanks,
Joe Mottram
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