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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents



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ID: 421376.0, MPI für Astronomie / Publikationen_mpia
Atmospheric refractivity effects on mid-infrared ELT adaptive optics
Authors:Kendrew, Sarah; Jolissaint, Laurent; Mathar, Richard J.; Stuik, Remko; Hippler, Stefan; Brandl, Bernhard
Language:English
Publisher:SPIE
Place of Publication:Bellingham, Wash.
Date of Publication (YYYY-MM-DD):2008
Title of Proceedings:Adaptive Optics Systems
Start Page:70155T-70155T
End Page:11
Title of Series:SPIE
Volume (in Series):7015
Name of Conference/Meeting:Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series
Review Status:not specified
Audience:Experts Only
Abstract / Description:We discuss the effect of atmospheric dispersion on the performance of a mid-infrared adaptive optics assisted instrument on an extremely large telescope (ELT). Dispersion and atmospheric chromaticity is generally considered to be negligible in this wavelength regime. It is shown here, however, that with the much-reduced diffraction limit size on an ELT and the need for diffraction-limited performance, refractivity phenomena should be carefully considered in the design and operation of such an instrument. We include an overview of the theory of refractivity, and the influence of infrared resonances caused by the presence of water vapour and other constituents in the atmosphere. 'Traditional' atmospheric dispersion is likely to cause a loss of Strehl only at the shortest wavelengths (L-band). A more likely source of error is the difference in wavelengths at which the wavefront is sensed and corrected, leading to pointing offsets between wavefront sensor and science instrument that evolve with time over a long exposure. Infrared radiation is also subject to additional turbulence caused by the presence of water vapour in the atmosphere not seen by visible wavefront sensors, whose effect is poorly understood. We make use of information obtained at radio wavelengths to make a first-order estimate of its effect on the performance of a mid-IR ground-based instrument. The calculations in this paper are performed using parameters from two different sites, one 'standard good site' and one 'high and dry site' to illustrate the importance of the choice of site for an ELT.
Comment of the Author/Creator:Date: 2008, July 1, 2008
External Publication Status:published
Document Type:Conference-Paper
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:URL:http://adsabs.harvard.edu/abs/2008SPIE.7015E.159K [ID No:1]
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