GeMS/GSAOI: towards regular astrometric distortion correction

The GeMS/GSAOI pair has been in regular science operation since 2013 at the Gemini South telescope and regularly delivers close to diffraction limited imaging in the NIR bands over a wide field of view of 85" square. Although the original GeMS/GSAOI science cases intentionally did not specify any astrometric performance, the Gemini users community expressed a large interest into using it with this purpose. Both instruments are subject to gravity-induced flexures. GSAOI is often dismounted from the telescope in instrument exchanges, making a regular on-sky calibration strategy time prohibitive. In 2017, we installed a new GeMS calibration focal plane mask offering ~1600 pinhole sources with a position accuracy of ±25 μm equivalent to ±0.4 mas, which can be used to deliver distortion calibration. We evaluate the flexure effect in the GeMS/GSAOI pair and discuss how to facilitate the mask to calibrate intra-night distortion drifts.