Deep HST Imaging in 47 Tuc and NGC 6397: Main Sequence Turnoff Ages

The ages of Galactic globular clusters provide insight into the formation history of the Milky Way. Utilizing HST photometry of unprecendented depth and wavelength coverage, we determine the main sequence turnoff ages of the nearby globular clusters NGC 6397 and 47 Tuc. The ages are determined by comparing stellar evolution models to the main sequences with a chi-squared minimization technique. Our analysis of 47 Tuc leverages the pronounced 'kink' or 'knee' feature that appears in the lower main sequence in the near-IR. We present our age estimates as probability distributions and construct confidence intervals over input parameters such as metallicity, distance, and reddening.