Tip-tilt anisoplanatism in MCAO-assisted astrometric observations

TL;DR

This paper analyzes how tip-tilt residuals caused by atmospheric turbulence affect the precision of astrometric measurements in MCAO systems, emphasizing the role of integration time and residual modeling.

Contribution

It provides a detailed analysis of tip-tilt residual effects on astrometry in MCAO systems, including modeling through temporal transfer functions and error budget estimation.

Findings

Tip-tilt residuals significantly impact astrometric accuracy.

Integration time influences the magnitude of residuals and errors.

The analysis aids in optimizing MCAO system performance for high-precision astrometry.

Abstract

A new era of ground-based observations, either in the infrared with the next-generation of 25-40m extremely large telescopes or in the visible with the 8m Very Large Telescope, is going to be assisted by multi-conjugate adaptive optics (MCAO) to restore the unprecedented resolutions potentially available for these systems in absence of atmospheric turbulence. Astrometry is one of the main science drivers, as MCAO can provide good quality and uniform correction over wide field of views ($\sim$ 1 arcmin) and offer a large number of reference sources with high image quality. The requirements have been set to very high precisions on the differential astrometry (e.g. 50$\mu$as for MICADO/MORFEO - formerly known as MAORY - at the Extremely Large Telescope) and an accurate analysis of the astrometric error budget is needed. In this context, we present an analysis of the impact of MCAO atmospheric tip-tilt residuals on relative astrometry. We focus on the effects of the scientific integration time on tip-tilt residuals, that we model through the temporal transfer function of the exposure. We define intra- and inter-exposure tip-tilt residuals that we use in the estimation of the centroiding error and the differential tilt jitter error within the astrometric error budget. As a case study, we apply our results in the context of the MORFEO astrometric error budget.