Adaptive optics (AO) is a technology that corrects in real time for the blurring e †ects of atmospheric turbulence, in principle allowing Earth-bound telescopes to achieve their di †raction limit and to "" see ÏÏ as clearly as if they were in space. The power of AO using natural guide stars has been amply demonstrated in recent years on telescopes up to 3È4 m in diameter. The next breakthrough in astronomical resolution was expected to occur with the implementation of AO on the new generation of large, 8È10 m diameter telescopes. In this paper we report the initial results from the Ðrst of these AO systems, now coming on line on the 10 m diameter Keck II Telescope. The results include the highest angular resolution images ever obtained from a single telescope and at 0.85 and 1.65 km wavelengths, respectively), as well (0A .022 0A .040 as tests of system performance on three astronomical targets.
ABSTRACT. We analyze stellar images on 36,520 exposures made in the u, g, r, i, and z bands with MegaCam at the focus of the 3.6 m Canada-France-Hawai′i Telescope between 2005 August and 2008 August. The effect on image quality (IQ) of temperature differences (ΔTs) in the telescope environment and of wind speed and direction are first examined and discussed. The contributions of the optics to image spread are then estimated and the frequency distribution of the observatory-free site seeing is obtained. The main findings are: (1) In the convective mode, the thermally-induced image full width at half-maximum intensity (FWHM) grows with the temperature gradient and path length L at the rate of ∼0:2″ · ðΔT=LÞ 6=5 · L 3=5 . (2) For a given jΔTj, thermal convection is ∼3 times more detrimental to image quality than thermal inversions. (3) The orientation of the dome slit with respect to the wind direction has important effects on IQ. (4) The median observatory induced seeing is 0.43″ FWHM. (5) The FWHM caused by the optics and slight optomechanical imperfections ranges from 0.46″ in u to 0.28″ in i. (6) The median DIMM-scale zenith atmospheric seeing at a wavelength of 500 nm and an elevation of 17 m above ground at the CFHT site is 0.55″. (7) The characteristics value of the outer scale of turbulence is 30 m. The paper addresses various issues bearing on the management of facility seeing.
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