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C. Roat, D. Wittman, J.A. Tyson (UC Davis)
The LSST deep catalog will be derived from hundreds of observations of each field in each filter. The first step is the creation of a single deep stacked image for each field in each filter. This stack is a highly compressed version of the LSST dataset and will be valuable for many applications which require speed and ease of handling rather than utmost accuracy, for example, quick images for viewing by the general public and for astronomers to conduct preliminary analysis, plan observations, match with other surveys, etc. However, some applications will require analysis of the full dataset using the stack and its associated catalog only as a starting point. One of these is weak lensing, for which full advantage must be taken of the best-seeing images. Although lensing is the driver for this work, the following approach should in principle also improve the accuracy of photometry, bulge/disk fits, star/galaxy separation, etc.
Galaxy shape parameter measurement for weak lensing studies will be done by simultaneously fitting individual exposures to a common profile model convolved with each exposure's point spread function (PSF) at that position in the image. This technique allows more accurate reconstruction of smaller galaxies than previous techniques that used co-addition of images because information is not degraded during the process of co-addition. Technically, the benefits of fitting individual exposures are: the direct incorporation of PSF estimation errors in the formal error calculation, and more reliable PSF interpolation since no dithering has occurred. Improvement over other techniques is quantified using current Deep Lens Survey data, which is compared against expectations from simulations for the LSST.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.