Using EMCCD's to improve the photometric precision of ground-based astronomical observations

We report on a novel data reduction technique that uses the fast, low-noise operation of EMCCD's to provide improvements in ground-based astronomical photometry of up to 48% by removing much of the incoherent wavelength-dependent absorption of the atmosphere. The technique has significant application potential in multicolour photometry where inter-colour short-timescale variability are particularly prone to atmospheric effects. We comment on a two-colour photometer we have developed to take advantage of the technique.