High-precision astrometry with a diffractive pupil telescope

Olivier Guyon, Eduardo A. Bendek, Josh A. Eisner, Roger Angel, Neville J. Woolf, Thomas D. Milster, S. Mark Ammons, Michael Shao, Stuart Shaklan, Marie Levine, Bijan Nemati, Joe Pitman, Robert A. Woodruff, Ruslan Belikov

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


Astrometric detection and mass determination of Earth-mass exoplanets require sub-μas accuracy, which is theoretically possible with an imaging space telescope using field stars as an astrometric reference. The measurement must, however, overcome astrometric distortions, which are much larger than the photon noise limit. To address this issue, we propose to generate faint stellar diffraction spikes using a two-dimensional grid of regularly spaced small dark spots added to the surface of the primary mirror (PM). Accurate astrometric motion of the host star is obtained by comparing the position of the spikes to the background field stars. The spikes do not contribute to scattered light in the central part of the field and therefore allow unperturbed coronagraphic observation of the star's immediate surroundings. Because the diffraction spikes are created on the PM and imaged on the same focal plane detector as the background stars, astrometric distortions affect equally the diffraction spikes and the background stars and are therefore calibrated. We describe the technique, detail how the data collected by the wide-field camera are used to derive astrometric motion, and identify the main sources of astrometric error using numerical simulations and analytical derivations. We find that the 1.4 m diameter telescope, 0.3 deg2 field we adopt as a baseline design achieves 0.2 μas single measurement astrometric accuracy. The diffractive pupil concept thus enables sub-μas astrometry without relying on the accurate pointing, external metrology, or high-stability hardware required with previously proposed high-precision astrometry concepts.

Original languageEnglish (US)
Article number11
JournalAstrophysical Journal, Supplement Series
Issue number2
StatePublished - Jun 2012


  • astrometry
  • planets and satellites: detection
  • techniques: high angular resolution
  • telescopes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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