Dalessandro, EmanueleEmanueleDalessandroSaracino, S.S.SaracinoORIGLIA, LiviaLiviaORIGLIAMarchetti, E.E.MarchettiFerraro, F. R.F. R.FerraroLanzoni, B.B.LanzoniGeisler, D.D.GeislerCohen, R. E.R. E.CohenMauro, F.F.MauroVillanova, S.S.Villanova2020-06-262020-06-2620160004-637Xhttp://hdl.handle.net/20.500.12386/26227Ground-based imagers at 8 m class telescopes assisted by multi-conjugate adaptive optics are primary facilities with which to obtain accurate photometry and proper motions in dense stellar fields. We observed the central region of the globular clusters Liller 1 and NGC 6624 with the Gemini Multi-conjugate Adaptive Optics System (GeMS) feeding the Gemini South Adaptive Optics Imager (GSAOI) currently available at the Gemini South telescope, under different observing conditions. We characterized the stellar point-spread function (PSF) in terms of FWHM, Strehl ratio (SR), and encircled energy (EE), over the field of view (FOV). We found that, for sub-arcsecond seeing at the observed airmass, we can obtain the diffraction-limited PSF (FWHM ≈ 80 mas), SR ∼ 40%, and EE ≥ 50% with a dispersion around 10% over the FOV of 85″ × 85″, in the K <SUB> s </SUB> band. In the J band the best images provide FWHMs between 60 and 80 mas, SR \gt 10 % , and {EE}\gt 40 % . For seeing at the observed airmass exceeding 1″, the performance worsens but it is still possible to perform PSF fitting photometry with 25% EE in J and 40% in K <SUB> s </SUB>. We also computed the geometric distortions of GeMS/GSAOI and we obtained corrected images with an astrometric accuracy of ∼1 mas in a stellar field with high crowding.STAMPAenArticle10.3847/1538-4357/833/1/1112-s2.0-85006340317000390765800007https://iopscience.iop.org/article/10.3847/1538-4357/833/1/1112016ApJ...833..111DFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation