Pushing the Limits of Near-Infrared Photometry with the Gemini Multi-Conjugate Adaptive Optics System: Study of crowded fields in the Globular Cluster M5

Abstract

Abstract We present the deepest J – Ks near-infrared photometry of the globular cluster M5 (NGC 5904) from observations taken with the Gemini South Adaptive Optics Imager in tandem with the Gemini Multi-conjugate adaptive optics System (GeMS) on the 8.1m Gemini-South telescope. Point spread function (PSF) photometry was carried out using a spatially variable PSF, zero point calibrations based on correlations to a standard photometric catalogue, colour corrections, and crowding corrections. The latter corrections provided a new challenge given the field variations of the adaptive optics corrections in the central crowded regions of this cluster. The final photometric precision in our J – Ks colour-magnitude diagram exposes a dispersion amongst the lower main-sequence stars of M5 for the first time. This dispersion occurs below a main-sequence knee due to variations in the helium and CNO abundances from multiple stellar populations, consistent with results from the bright evolved stars in this cluster from ultraviolet to near-infrared Hubble Space Telescope photometry and ground-based spectroscopy. This paper completes our original GeMS quality analysis program, providing insights into adaptive optics analyses in crowded fields.