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Proceedings Paper

Theoretical limits on bright star astrometry with multi-conjugate adaptive optics using a diffractive pupil
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Paper Abstract

We present a ground-based technique to detect or follow-up long-period exoplanets via precise relative astrometry of host stars using Multi-Conjugate Adaptive Optics (MCAO) on 8 meter telescopes equipped with diffractive masks. MCAO improves relative astrometry by sharpening PSFs, reducing the star centroiding error, and by providing a spatially stable, more easily modeled PSF. However, exoplanet mass determination requires multi-year reference grid stability of ~10-100 uas or nanometer-level stability on the long-term average of out-of-pupil phase errors, which is difficult to achieve with MCAO. The diffractive pupil technique calibrates dynamic distortion via extended diffraction spikes generated by a dotted primary mirror, which are referenced against a grid of background stars. We calculate the astrometic performance of a diffractive 8-meter telescope with diffraction-limited MCAO in K using analytical techniques and a simplified MCAO simulation. Referencing the stellar grid to the diffraction spikes negates the cancellation of Differential Tip/Tilt Jitter normally achieved with MCAO. However, due to the substantial gains associated with sharper, more stable PSFs, diffractive 8-m MCAO reaches ~ 4-6 μas relative astrometric error per coordinate in one hour on a bright target star (K ~ 7) in fields of moderate stellar density (~10 stars arcmin-2). Final relative astrometric precision with MCAO is limited by atmospheric differential tip/tilt jitter.

Paper Details

Date Published: 13 September 2012
PDF: 9 pages
Proc. SPIE 8447, Adaptive Optics Systems III, 84470P (13 September 2012); doi: 10.1117/12.927281
Show Author Affiliations
S. Mark Ammons, Lawrence Livermore National Lab. (United States)
Eduardo A. Bendek, Steward Observatory, The Univ. of Arizona (United States)
Olivier Guyon, Steward Observatory, The Univ. of Arizona (United States)
Subaru Telescope (United States)
Bruce Macintosh, Lawrence Livermore National Lab. (United States)
Dmitry Savransky, Lawrence Livermore National Lab. (United States)

Published in SPIE Proceedings Vol. 8447:
Adaptive Optics Systems III
Brent L. Ellerbroek; Enrico Marchetti; Jean-Pierre Véran, Editor(s)

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