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

S. Mark Ammons, Eduardo A. Bendek, Olivier Guyon, Bruce Macintosh, Dmitry Savransky

Research output: Chapter in Book/Report/Conference proceedingConference contribution

8 Scopus citations


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.

Original languageEnglish (US)
Title of host publicationAdaptive Optics Systems III
StatePublished - 2012
EventAdaptive Optics Systems III - Amsterdam, Netherlands
Duration: Jul 1 2012Jul 6 2012

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


OtherAdaptive Optics Systems III


  • Adaptive optics
  • Astrometry
  • Differential atmospheric refraction
  • Differential tip/tilt jitter
  • Diffractive pupil
  • Exoearth
  • Extrasolar planet
  • MCAO
  • Microarcsecond
  • PECO
  • SIM

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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