GeMS/GSAOI photometric and astrometric performance in dense stellar fields

Abstract

Ground-based imagers at 8m class telescopes assisted by Multi conjugate Adaptive Optics are primary facilities 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 Full Width at Half Maximum (FWHM), Strehl Ratio (SR) and Encircled Energy (EE), over the field of view. We found that, for sub-arcsec seeing at the observed airmass, diffraction limit PSF FWHM ($\approx$ 80 mas), SR $\sim 40\%$ and EE $\ge 50\%$ with a dispersion around $10\%$ over the 85" x 85" field of view, can be obtained in the $K_s$ band. In the $J$ band the best images provide FWHMs between 60 and 80 mas, SR $>10\%$ and EE $>40\%$. For seeing at the observed airmass exceeding 1", the performance worsen but it is still possible to perform PSF fitting photometry with $25\%$ EE in $J$ and $40\%$ in $K_s$. We also computed the geometric distortions of GeMS/GSAOI and we obtained corrected images with an astrometric accuracy of $\sim$1 mas in a stellar field with high crowding.

32 pages, 13 figures, 4 tables; accepted for publication in ApJ

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• A panchromatic view of the bulge globular cluster NGC 6569
• Clues to the formation of Liller 1 from modeling its complex star formation history
• Towards Realistic Modeling of the Astrometric Capabilities of MCAO Systems: Detecting an Intermediate Mass Black Hole with MAVIS
• Unveiling the nature of the Gemini multiconjugate adaptive optics system distortions
• MUSE narrow field mode observations of the central kinematics of M15
• The Bulge Cluster Origin (BulCO) survey at the ESO-VLT: probing the early history of the Milky Way assembling. Design and first results in Liller1
• Successful application of PSF-R techniques to the case of the globular cluster NGC6121 (M4)
• The bulge globular cluster Terzan 6 as seen from multi-conjugate adaptive optics and HST
• Optimal Differential Astrometry for Multiconjugate Adaptive Optics. I. Astrometric Distortion Mapping using On-sky GeMS Observations of NGC 6723
• First sodium laser guide star asterism launching platform in China on 1.8m telescope at Gaomeigu Observatory
• The impact of geometric distortions in multiconjugate adaptive optics astrometric observations with future extremely large telescopes
• Multi-conjugated adaptive optics imaging of distant galaxies -- A comparison of Gemini/GSAOI and VLT/HAWK-I data