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Published June 2006 | Published
Journal Article Open

The anisoplanatic point-spread function in adaptive optics

Britton, M. C.

Abstract

The effects of anisoplanatism on the adaptive optics point‐spread function are investigated. A model is derived that combines observations of the guide star with an analytic formulation of anisoplanatism in order to generate predictions for the adaptive optics point‐spread function at arbitrary locations within the field of view. The analytic formulation captures the dependencies of anisoplanatism on aperture diameter, observing wavelength, angular offset, zenith angle, and turbulence profile. The predictions of this model are compared to narrowband 2.12 and 1.65 μm images of a 21" binary (m_v = 7.3, 7.6) acquired with the Palomar adaptive optics system on the 5 m Hale Telescope. Contemporaneous measurements of the turbulence profile made with a DIMM/MASS (differential image motion monitor/multiaperture scintillation sensor) unit are used together with images of the primary to predict the point‐spread function of the binary companion. Predicted companion Strehl ratios are shown to match measurements to within a few percent, whereas predictions based on the isoplanatic angle approximation are highly discrepant. The predicted companion point‐spread functions are shown to agree with observations to 10%. These predictions are used to measure the differential photometry between binary members to an accuracy of 1 part in 10^3, and the differential astrometry to an accuracy of 1 mas. Errors in the differential astrometry are shown to be dominated by differential atmospheric tilt jitter. These results are compared to other techniques that have been employed for photometry, astrometry, and high‐contrast imaging.

Additional Information

© 2006 Astronomical Society of the Pacific. Received 2006 March 7; accepted 2006 May 2; published 2006 June 28. The author would like to thank many colleagues who participated in discussions of this research, including Brent Ellerbroek, Richard Dekany, Mitchell Troy, Andrei Tokovinin, Keith Taylor, Andrew Pickles, Roger Smith, Don Gavel, and Matthias Schoeck. The author gratefully acknowledges the efforts of the Thirty Meter Telescope site-testing group and the Palomar Observatory staff in setting up and maintaining the turbulence-monitoring equipment at Palomar Observatory. This paper was prepared as part of the work of the Thirty Meter Telescope (TMT) project. TMT is a partnership of the Association of Universities for Research in Astronomy, Inc. (AURA), the Association of Canadian Universities for Research in Astronomy (ACURA), the California Institute of Technology, and the University of California. The partners gratefully acknowledge the support of the Gordon and Betty Moore Foundation, the US National Science Foundation (NSF), the National Research Council of Canada, the Natural Sciences and Engineering Research Council of Canada, and the Gemini Partnership. This work has also been supported by the National Science Foundation Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement AST 98-76783.

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August 19, 2023
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October 23, 2023