My area of research is stellar astronomy and I am interested in what resolved systems of stars can tell us about planet formation, dark matter, the age of the Universe, the dynamical evolution of stellar systems and the formation of galaxies. To investigate these diverse subjects I observe a wide range of objects including nearby stars, open and globular star clusters and the resolved components of our neighbouring galaxies. To accomplish my research goals I use a variety of telescopes particularly the twin Gemini Telescopes, the Canada France Hawaii Telescope and the Hubble Space Telescope.
 One area of current interest is a search for the oldest white dwarfs. In the right environments, extremely cool white dwarfs can be used to check on the chronology of stellar systems and provide age estimates largely independent of the usual assumptions of stellar evolution theory. Ages of stellar systems using white dwarfs are currently being derived for open clusters, the Galactic halo and globular star clusters. The eventual aim is that these ages will confront ages derived from stellar evolution and from cosmology and lead to new insights into cosmology. A current project of particular interest is our work on the metal-poor globular star cluster NGC 6397. We obtained images totaling 126 orbits with the Hubble Space Telescope in this cluster and have reached both the termination of the hydrogen-burning main sequence as well as the truncation in the white dwarf cooling sequence as seen in the figure above. This truncation is the limit to which the bulk of the white dwarfs have cooled to over the lifetime of the cluster and will be an important diagnostic in determining the cluster age. In the photo below I illustrate a small portion of the deep ACS image in NGC 6397 highlighting a faint cluster white dwarf (above insert) and a star very close to the theoretically predicted hydrogen burning limit.  |