Photometric performance of LGS MCAO with science-based metrics: first results from Gemini/GeMS observations of Galactic globular clusters

摘要

Multi-conjugate adaptive optics can achieve diffraction limited images over a field of arcminutes and is a central technology for the future ELTs: Gemini/GeMS is the first facility-class LGS MCAO system to operate. With it we have taken images in J and Ks bands of the globular cluster NGC 1851 for which we also have HST/ACS observations in the visible. In this paper we present the deepest to date near-infrared photometry of NGC 1851 providing a wide colour baseline CMD that reaches the lower main sequence to have a new insight into the stellar populations of this globular cluster. The use of the GGCs' lower main sequence knee to determine its age is one of the science drivers for the observation of GGCs with MCAO given its visibility in the infrared and because it requires high Strehl ratios to measure the faint stars' photometry. In addition to the stellar population analysis, these data allow to examine the photometric performance of the instrument using a large number of point sources distributed across the field. We analyze the photometric performance of the instrument and the field dependence of the PSF, a central part on the prediction and improvement of the performance of future LGS MCAO systems like NFIRAOS for the Thirty Meter Telescope.