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Hello all, I have a fairly simple question. It's about performing photometry measurements on GMOS data. Since GMOS has three detectors, each of them with their own gain, rdnoise and bias levels, images are then multiplied (at the processing stage by gireduce) by the gain in each detector to transform ADUs to electros. So fluxes now are in electrons.
Without knowing this, I've performed the usual photometry with apphot and then realized about that, by looking at the magnitude errors that looked funny.
So the question is:
It is only in the error estimation (sky and magnitudes) that the gain value is used within apphot? If that's true, it won't be a problem to have fluxes in electrons and carry on.(from apphot)
[code:1:b4c5468098]
flux = sum - area * msky (ADUs)
mag = zmag - 2.5 * log10 (flux) + 2.5 * log10 (itime)
merr = 1.0857 * err / flux
err = sqrt (flux / epadu + area * stdev**2 +
area**2 * stdev**2 / nsky)
[/code:1:b4c5468098]Also, since fluxes are in electrons, I bet that I should need to modify the SNR to account for values in electrons and not in ADUs to use
[code:1:b4c5468098]
errmag ~2.5*log10(1+1/SNR)
[/code:1:b4c5468098]
Thank you in advance!
Cheers,
sebastian