Unveiling the nature of Gemini multiconjugate adaptive optics system distortions

Abstract Astrometry was not a science case of the Gemini Multiconjugate Adaptive Optics System (GeMS) at its design stage. However, since GeMS has been in regular science operation with the Gemini South Adaptive Optics Imager (GSAOI), its astrometric performance has been deeply analysed. The non-linear component of the distortion-map model shows a characteristic pattern, which is similarly repeated in each detector of GSAOI. The nature of this pattern was unknown and subjected to different hypotheses. This article describes the origin of the GeMS distortion pattern, as well as its multi-epoch variation. Finally, we show a comparison with the current design of the Multiconjugate Adaptive Optics RelaY (MAORY) of the Extremely Large Telescope (ELT).