Hi everyone,
for those of you who have been working on GeMS+GSAOI images , I’d like to share some of my experience on their photometric data reduction. During the GeMS’ Science Verification phase we have observed the Galactic globular cluster NGC 1851 to get precise photometry of this crowded stellar field (Turri et al. 2015).
Some of the choices usually adopted to reduce seeing limited data have to be adjusted to the peculiarity of MCAO PSFs to improve the quality of photometric (and possibly astrometric) results. I’ve performed the analysis using DAOPHOT but here I will make general suggestions useful with any profile fitting program.
I will break my post into several short parts starting with an introduction on the selection of stars for the profile fitting photometry. I will later talk about how the PSF varies spatially and temporally, what are the effects of the PSF size and crowding on the photometry and finally about the method used for the photometric calibration.
Stay tuned for the next part and please feel free to ask questions at any point.

Cheers,
Paolo