Issue |
A&A
Volume 689, September 2024
|
|
---|---|---|
Article Number | A94 | |
Number of page(s) | 17 | |
Section | Celestial mechanics and astrometry | |
DOI | https://doi.org/10.1051/0004-6361/202449734 | |
Published online | 06 September 2024 |
Differential image motion in astrometric observations with very large seeing-limited telescopes*
1
Main Astronomical Observatory, National Academy of Sciences of the Ukraine,
Zabolotnogo 27,
03680
Kyiv,
Ukraine
e-mail: laz@mao.kiev.ua
2
European Space Agency (ESA), European Space Astronomy Centre (ESAC),
Camino Bajo del Castillo s/n,
28692
Villanueva de la Cañada, Madrid,
Spain
3
Observatoire de Genève, Université de Genève,
51 Chemin Des Maillettes,
1290
Versoix,
Switzerland
4
Instituto de Astrofísica de Canarias, calle Víal Láctea,
San Cristóbal de La Laguna,
Spain
Received:
26
February
2024
Accepted:
11
July
2024
Aims. We investigate how to quantitatively model the observed differential image motion (DIM) in relative astrometric observations.
Methods. As a test bed we used differential astrometric observations from the FORS2 camera of the Very Large Telescope (VLT) obtained during 2010–2019 under several programs of observations of southern brown dwarfs. The measured image motion was compared to models that decompose atmospheric turbulence in frequency space and translate the vertical turbulence profile into DIM amplitude. This approach accounts for the spatial filtering by the telescope’s entrance pupil and the observation parameters (field size, zenith angle, reference star brightness and distribution, and exposure time), and it aggregates that information into a newly defined metric integral term.
Results. We demonstrate excellent agreement (within 1%) between the model parameters derived from the DIM variance and determined by the observations. For a 30 s exposure of a typical 1′-radius field close to the Galactic plane, image motion limits astrometric precision to ~60 μas when sixth-order transformation polynomial is applicable. We confirm that the measured image motion variance is well described by Kolmogorov-type turbulence with exponent 11/3 dependence on the field size at effective altitudes of 16–18 km, where the best part of the DIM is generated. Extrapolation to observations with extremely large telescopes enables the estimation of the astrometric precision limit for seeing-limited observations of ~5 μas, which has a variety of exciting scientific applications.
Key words: atmospheric effects / methods: data analysis / techniques: high angular resolution / astrometry
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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