High-precision astrometry towards ELTs

TL;DR

This study evaluates the potential for high-precision astrometry with the upcoming ELT, emphasizing the importance of atmospheric dispersion correction and distortion modeling to achieve milliarcsecond accuracy.

Contribution

It demonstrates the expected improvements from an atmospheric dispersion corrector and develops a distortion correction model using current adaptive optics data.

Findings

ADC can improve positional accuracy by up to ~2 mas.

Distortions can reach ~200 mas and be corrected to ~1 mas.

Both ADC and distortion modeling are essential for future ELT astrometry.

Abstract

With the aim of paving the road for future accurate astrometry with MICADO at the European-ELT, we performed an astrometric study using two different but complementary approaches to investigate two critical components that contribute to the total astrometric accuracy. First, we tested the predicted improvement in the astrometric measurements with the use of an atmospheric dispersion corrector (ADC) by simulating realistic images of a crowded Galactic globular cluster. We found that the positional measurement accuracy should be improved by up to ~2 mas with the ADC, making this component fundamental for high-precision astrometry. Second, we analysed observations of a globular cluster taken with the only currently available Multi-Conjugate Adaptive Optics assisted camera, GeMS/GSAOI at Gemini South. Making use of previously measured proper motions of stars in the field of view, we were able to model the distortions affecting the stellar positions. We found that they can be as large as ~200 mas, and that our best model corrects them to an accuracy of ~1 mas. We conclude that future astrometric studies with MICADO requires both an ADC and an accurate modelling of distortions to the field of view, either through an a-priori calibration or an a-posteriori correction.