A Multi-Conjugate Adaptive Optics view of Bulge Globular Clusters

Abstract

The Galactic bulge is one of the most massive and inaccessible regions of the Galaxy, where thick clouds of dust along the line of sight almost totally absorb the optical light. Bulge globular clusters (GCs) are useful tools to constrain the properties of this system, as they share the same kinematics and chemical composition with bulge field stars. However, these systems have been widely excluded from large surveys due to the huge extinction, and they remain in many cases only poorly known so far. The aim of this Thesis is to contribute to fill this gap by studying the stellar populations and structural parameters of bulge GCs by means of state-of- the-art high resolution near-infrared (NIR) instruments. We exploited the capabilities offered by the Multi-Conjugate Adaptive Optics system GeMS combined with the GSAOI imager at the Gemini South Telescope, in Chile. We mainly focused on two extreme cases. The first is Liller 1, one of the most obscured and therefore least studied systems in the Galaxy. It probe the benefit of using an Adaptive Optics system on an 8 meter telescope. The second is NGC 6624, which is well-studied and therefore allows a detailed comparison and assessment of the GeMS+GSAOI performance. Based on these data we performed an in-depth characterization of the instruments in terms of Point Spread Function modeling, Strehl Ratio and Encircled Energy distribution variations within the field of view. We derived also the first analytic solution to correct the geometric distortions of this system. Taking advantage of the exquisite quality and depth of the NGC 6624 images, in combination with deep HST NIR observations of 47 Tucanae, we performed a detailed analysis aimed at probing reliability and limits of the so-called MS-knee as a tool to derive accurate absolute ages in NIR CMDs of GC.