A New Algorithm for Point‐Spread Function Subtraction in High‐Contrast Imaging: A Demonstration with Angular Differential Imaging

Direct imaging of exoplanets is limited by bright quasi-static speckles inthe point spread function (PSF) of the central star. This limitation can bereduced by subtraction of reference PSF images. We have developed an algorithmto construct an optimized reference PSF image from a set of reference images.This image is built as a linear combination of the reference images availableand the coefficients of the combination are optimized inside multiplesubsections of the image independently to minimize the residual noise withineach subsection. The algorithm developed can be used with many high-contrastimaging observing strategies relying on PSF subtraction, such as angulardifferential imaging (ADI), roll subtraction, spectral differential imaging,reference star observations, etc. The performance of the algorithm isdemonstrated for ADI data. It is shown that for this type of data the newalgorithm provides a gain in sensitivity by up to a factor 3 at smallseparation over the algorithm used in Marois et al. (2006).Comment: 7 pages, 11 figures, to appear in May 10, 2007 issue of Ap