A Fourier optics approach to evaluate the astrometric performance of MICADO

TL;DR

This paper develops a Fourier Optics framework to analyze how wavefront errors affect the high-precision astrometric measurements of MICADO, an upcoming near-infrared instrument for the ELT, considering various error sources.

Contribution

It introduces a comprehensive Fourier Optics approach to evaluate PSF centroid shifts due to wavefront errors, aiding in the performance assessment of MICADO.

Findings

Modeling of wavefront errors using Zernike polynomials and PSD analysis.

Assessment of PSF centroid shifts as a function of wavefront errors.

Framework enables detailed evaluation of MICADO's astrometric accuracy.

Abstract

We present our investigation into the impact of wavefront errors on high accuracy astrometry using Fourier Optics. MICADO, the upcoming near-IR imaging instrument for the Extremely Large Telescope, will offer capabilities for relative astrometry with an accuracy of 50 micro arcseconds ({\mu}as). Due to the large size of the point spread function (PSF) compared to the astrometric requirement, the detailed shape and position of the PSF on the detector must be well understood. Furthermore, because the atmospheric dispersion corrector of MICADO is a moving component within an otherwise mostly static instrument, it might not be sufficient to perform a simple pre-observation calibration. Therefore, we have built a Fourier Optics framework, allowing us to evaluate the small changes in the centroid position of the PSF as a function of wavefront error. For a complete evaluation, we model both the low order surface form errors, using Zernike polynomials, and the mid- and high-spatial frequencies, using Power Spectral Density analysis. The described work will then make it possible, performing full diffractive beam propagation, to assess the expected astrometric performance of MICADO.