Paper detail

MAD about the Large Magellanic Cloud: preparing for the era of Extremely Large Telescopes

We present J, H, Ks photometry from the the Multi conjugate Adaptive optics Demonstrator (MAD), a visitor instrument at the VLT, of a resolved stellar population in a small crowded field in the bar of the Large Magellanic Cloud near the globular cluster NGC 1928. In a total exposure time of 6, 36 and 20 minutes, magnitude limits were achieved of J \sim 20.5 mag, H \sim 21 mag, and Ks \sim20.5 mag respectively, with S/N> 10. This does not reach the level of the oldest Main Sequence Turnoffs, however the resulting Colour-Magnitude Diagrams are the deepest and most accurate obtained so far in the infrared for the LMC bar. We combined our photometry with deep optical photometry from the Hubble Space Telescope/Advanced Camera for Surveys, which is a good match in spatial resolution. The comparison between synthetic and observed CMDs shows that the stellar population of the field we observed is consistent with the star formation history expected for the LMC bar, and that all combinations of IJHKs filters can, with some care, produce the same results. We used the Red Clump magnitude in Ks to confirm the LMC distance modulus as, μ0=18.50\pm0.06r \pm0.09s mag. We also addressed a number of technical aspects related to performing accurate photometry with adaptive optics images in crowded stellar fields, which has implications for how we should design and use the Extremely Large Telescopes of the future for studies of this kind.