Optical wavefront reconstruction algorithms played a central role in the effort to identify gross manufacturing errors in NASA's Hubble Space Telescope (HST). NASA's success with reconstruction algorithms on the HST has lead to an effort to develop software that can aid and in some cases replace complicated, expensive and error-prone hardware. Among the many applications is HST's replacement, the Next Generation Space Telescope (NGST).This work details the theory of optical wavefront reconstruction, reviews some numerical methods for this problem, and presents a novel numerical technique which we call extended least squares. We compare the performance of these numerical methods for potential inclusion in prototype NGST optical wavefront reconstruction software. We begin with a tutorial of Rayleigh-Sommerfeld diffraction theory.

We report Chandra ACIS-S3 x-ray imaging and spectroscopy of the R Aquarii binary system that show a spatially resolved two-sided jet and an unresolved central source. This is the first published report of such an x-ray jet seen in an evolved stellar system comprised of ~2-3 M (also see Kellogg et al 2000). At E < 1 keV, the x-ray jet extends both to the northeast and southwest relative to the central binary system. At 1 < E < 7.1 keV, R Aqr is a point-like source centered on the star system. While both 3.5-cm radio continuum emission and x-ray emission appear coincident in projection and have maximum intensities at ~7.5" NE of the central binary system, the next strongest x-ray component is located ~30" SW of the central binary system and has no radio continuum counterpart. The x-ray jets are likely shock heated in the recent past, and are not in thermal equilibrium. The strongest SW x-ray jet component may have been shocked recently since there is no relic radio emission as expected from an older shock. At the position of the central binary, we detect x-ray emission below 1.6 keV consistent with blackbody emission at T ~ 2 × 10 6 K. There is also a prominent 6.4 keV feature, a possible fluorescence or collisionally excited Fe Kα line from an accretion disk or from the wind of the giant star. For this excitation to occur, there must be an unseen hard source of x-rays or particles in the immediate vicinity of the hot star. Such a source would be hidden from view by the surrounding edge-on accretion disk.

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