Sky coverage estimates for the natural guide star mode of the TMT facility AO system NFIRAOS

B. Ellerbroek; David Andersen

doi:10.1117/12.788053

15 July 2008 Sky coverage estimates for the natural guide star mode of the TMT facility AO system NFIRAOS

B. Ellerbroek, David Andersen

Proceedings Volume 7015, Adaptive Optics Systems; 70155W (2008) https://doi.org/10.1117/12.788053
Event: SPIE Astronomical Telescopes + Instrumentation, 2008, Marseille, France

Abstract

Although the TMT AO system NFIRAOS will operate primarily in a laser guidestar multi-conjugate AO mode, it will also provide a conventional natural guide star (NGS) mode for use on very narrow science fields containing a bright star and/or when laser propagation is prevented by thin cirrus clouds or other circumstances. The number of bright stars suitable for use with a high order AO system is limited, so we have performed a sky coverage analysis to determine the likelyhood of achieving a given Strehl ratio when observing a randomly selected science field. The results obtained are significantly better than for existing NGS AO systems, largely due to (i) the anticipated availability of large, high-speed detector arrays with sub-electron read noise, and (ii) the benign telescope windshake disturbances predicted for TMT. Order 60×60 wavefront sensing and correction is preferred to lower order AO compensation, and an H-band Strehl of 0.25 [0.50] is obtained with sky coverage of about 1.0 [0.1] per cent at the Galactic pole in median seeing. This level of performance will provide an important capability for TMT well into the life of the observatory.

Citation Download Citation

B. Ellerbroek and David Andersen "Sky coverage estimates for the natural guide star mode of the TMT facility AO system NFIRAOS", Proc. SPIE 7015, Adaptive Optics Systems, 70155W (15 July 2008); https://doi.org/10.1117/12.788053

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