The GeMS/GSAOI Galactic Globular Cluster Survey (G4CS) I: A Pilot Study
  of the stellar populations in NGC 2298 and NGC 3201
  We present the first results from the GeMS/GSAOI Galactic Globular Cluster
Survey (G4CS) of the Milky-Way globular clusters (GCs) NGC 3201 and NGC 2298.
Using the Gemini South Adaptive Optics Imager (GSAOI), in tandem with the
Gemini Multi-conjugate adaptive optics System (GeMS) on the 8.1-meter
Gemini-South telescope, we collected deep near-IR observations of both
clusters, resolving their constituent stellar populations down to $K_s\simeq21$
Vega mag. Point spread function (PSF) photometry was performed on the data
using spatially-variable PSFs to generate $JHK_{s}$ photometric catalogues for
both clusters. These catalogues were combined with Hubble Space Telescope (HST)
data to augment the photometric wavelength coverage, yielding catalogues that
span the near-ultraviolet (UV) to near-infrared (near-IR). We then applied 0.14
mas/year accurate proper-motion cleaning, differential-reddening corrections
and chose to anchor our isochrones using the lower main-sequence knee (MSK) and
the main-sequence turn-off (MSTO) prior to age determination. As a result of
the data quality, we found that the $K_{s}$ vs. F606W$-K_{s}$ and F336W vs.
F336W$-K_{s}$ color-magnitude diagrams (CMDs) were the most diagnostically
powerful. We used these two color combinations to derive the stellar-population
ages, distances and reddening values for both clusters. Following
isochrone-fitting using three different isochrone sets, we derived best-fit
absolute ages of $12.2\pm0.5$ Gyr and $13.2\pm0.4$ Gyr for NGC 3201 and NGC
2298, respectively. This was done using a weighted average over the two
aforementioned color combinations, following a pseudo-$\chi^2$ determination of
the best-fit isochrone set. Our derived parameters are in good agreement with
recent age determinations of the two clusters, with our constraints on the ages
being or ranking among the most statistically robust.
