EDP Sciences
Free Access
Volume 427, Number 3, December I 2004
Page(s) 1127 - 1143
Section Celestial mechanics and astrometry
DOI https://doi.org/10.1051/0004-6361:20041481
Published online 16 November 2004

A&A 427, 1127-1143 (2004)
DOI: 10.1051/0004-6361:20041481

Filtration of atmospheric noise in narrow-field astrometry with very large telescopes

P. F. Lazorenko and G. A. Lazorenko

Main Astronomical Observatory, National Academy of Sciencies of the Ukraine, Zabolotnogo 27, 03680 Kyiv-127, Ukraine
    e-mail: laz@mao.kiev.ua

(Received 17 June 2004 / Accepted 19 July 2004)

This paper presents a non-classic approach to narrow field astrometry that offers a significant improvement over conventional techniques due to enhanced reduction of atmospheric image motion. The method is based on two key elements: apodization of the entrance pupil and the enhanced virtual symmetry of reference stars. Symmetrization is implemented by setting special weights to each reference star. Thus a reference field itself forms a virtual net filter that effectively attenuates the image motion spectrum. Atmospheric positional error was found to follow a power dependency $\Delta \sim R^{k \mu/2} D^{-k/2+1/3}$ on angular field size R and aperture D; here k is some optional even integer $2 \leq k \leq \sqrt{8N+1}-1$ limited by a number N of reference stars, and $\mu \leq 1$ is a term dependent on k and the magnitude and sky star distribution in the field. As compared to conventional techniques for which k=2, the improvement in accuracy increases by some orders. Limitations to astrometric performance of monopupil large ground-based telescopes are estimated. The total atmospheric and photon noise for at a 10 m telescope at good  0.4'' seeing was found to be, depending on sky star density, 10 to 60  $\mu$as per 10 min exposure in R band. For a 100 m telescope and FWHM =  0.1'' (low-order adaptive optics corrections) the potential accuracy is 0.2 to 2  $\mu$as.

Key words: atmospheric effects -- turbulence -- methods: data analysis -- astrometry -- instrumentation: high angular resolution

© ESO 2004

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