GeMS/GSAOI photometric and astrometric performance in dense stellar fields

TL;DR

This study evaluates the photometric and astrometric performance of the GeMS/GSAOI system in dense stellar fields, demonstrating high-resolution imaging capabilities and precise astrometry under various observing conditions.

Contribution

It provides a detailed characterization of GeMS/GSAOI's PSF, photometric quality, and astrometric accuracy in dense globular cluster fields, highlighting its performance limits and capabilities.

Findings

Achieves diffraction-limited PSF FWHM (~80 mas) in Ks band under good seeing conditions.

Attains astrometric accuracy of approximately 1 mas in crowded stellar fields.

Provides performance metrics for different bands and seeing conditions, guiding future observations.

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 $\sim40\%$ and EE $\ge50\%$ 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.