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28 June 2006 Water vapor measurement and compensation in the near- and mid-infrared with the Keck Interferometer Nuller
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Abstract
Water vapor is the dominant source of randomly-changing atmospheric dispersion on timescales of seconds to minutes in the near- and mid-infrared. The dispersion changes are sufficient to limit the performance of the Keck Nuller unless steps are taken to measure and compensate for them. Here we present the first measurements of water vapor differential column fluctuations with the mid-infrared Keck Nuller and its near-infrared fringe tracker, taken in October 2005, and discuss theoretical and practical aspects of our dispersion feedforward implementation. The data show much larger fluctuations than were seen in median Mauna Kea conditions measured at radio wavelengths, and probably account for the generally poor performance of the Nuller during the observing run. The measurements in the two bands show strong correlations, indicating that the planned feedforward of the near-infrared value to stabilize the dispersion in the mid-infrared will substantially reduce the residual dispersion fluctuations seen by the Nuller.
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Chris Koresko, M. Mark Colavita, Eugene Serabyn, Andrew Booth, and Jean Garcia "Water vapor measurement and compensation in the near- and mid-infrared with the Keck Interferometer Nuller", Proc. SPIE 6268, Advances in Stellar Interferometry, 626817 (28 June 2006); https://doi.org/10.1117/12.672434
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