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K. J. Lindsay, A. M. Koekemoer (STScI)
We provide an examination of optimal dither patterns for the James Webb Space Telescope (JWST) instruments. The general motivation for dithering is to improve photometric fidelity by moving sources to a number of locations within the shutter apertures, and to mitigate photometric uncertainties. The study is preliminary in its scope, as the design for each JWST instrument has not been finalized. However, current knowledge of the instruments added to extensive prior experience with the Hubble Space Telescope (HST) has allowed for a relatively robust investigation of a number of aspects of dither patterns that will be relevant for JWST. Although this study is based primarily on the NIRCam instrument, as its design and observational characteristics are sufficiently well defined, the other instruments are also considered in a more general fashion. Through use of simulated NIRCam images, we demonstrate how quantitative measurements of morphological, astrometric, and photometric properties allow for a direct comparison between different dither patterns and the intrinsic properties of the sources. We examine the benefits incurred from dithering, against the fractional increase in overhead time associated with each observing scenario. Based on these properties, we define metrics to describe and quantify the relative merits of different dither patterns or observing scenarios, based on instrumental properties and observing overheads. This work was supported by NASA contract NAS5-03127 for support of the JWST Science and Operations Center at the Space Telescope Science Institute.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.