Microarcsecond astrometry with MCAO using a diffractive mask

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

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

1 Scopus citations

Abstract

We present a new ground-based technique to detect or follow-up long-period, potentially habitable 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 both by cancellation of high-altitude atmospheric layers, which induce dynamic focal-plane distortions, and the improvement of centroiding precision with sharper PSFs. However, mass determination of habitable exoplanets requires multi-year reference grid stability of ~1-10 μas or nanometer-level stability on the long-term average of out-of-pupil phase errors, which is difficult to achieve with MCAO (e.g., Meyer et al. 2011). 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 (Guyon et al. 2012). The diffractive grid provides three benefits to relative astrometry: (1) increased dynamic range, permitting observation of V < 10 stars without saturation; (2) calibration of dynamic distortion; and (3) a spectrum of the target star, which can be used to calibrate the magnitude of differential atmospheric refraction to the microarcsecond level. A diffractive 8-meter telescope with diffraction-limited MCAO in K-band reaches < 3-5 μas relative astrometric error per coordinate perpendicular to the zenith vector in one hour on a bright target star in fields of moderate stellar density (~10-40 stars arcmin-2). We present preliminary on-sky results of a test of the diffractive mask on the Nickel telescope at Lick Observatory.

Original languageEnglish (US)
Title of host publicationProceedings of the International Astronomical Union
PublisherCambridge University Press
Pages369-374
Number of pages6
Volume8
EditionS293
ISBN (Print)9781107033825
DOIs
Publication statusPublished - 2012

Publication series

NameProceedings of the International Astronomical Union
NumberS293
Volume8
ISSN (Print)17439213
ISSN (Electronic)17439221

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Keywords

  • astrometry
  • instrumentation: adaptive optics
  • stars: planetary systems
  • techniques:high angular resolution

ASJC Scopus subject areas

  • Astronomy and Astrophysics

Cite this

Ammons, S. M., Bendek, E. A., Guyon, O., Macintosh, B., & Savransky, D. (2012). Microarcsecond astrometry with MCAO using a diffractive mask. In Proceedings of the International Astronomical Union (S293 ed., Vol. 8, pp. 369-374). (Proceedings of the International Astronomical Union; Vol. 8, No. S293). Cambridge University Press. https://doi.org/10.1017/S1743921313013173