What is limiting near-infrared astrometry in the Galactic Center?

TL;DR

This paper identifies key error sources limiting high-precision near-infrared astrometry in the Galactic Center, emphasizing the importance of advanced adaptive optics and halo reconstruction techniques for improvement.

Contribution

It systematically analyzes and quantifies the dominant error sources affecting astrometric accuracy in crowded stellar fields, guiding future improvements.

Findings

Imperfect halo subtraction and image distortions are primary error sources.

Residual distortions limit bright star astrometry, seeing halos affect fainter stars.

High-performance adaptive optics with small field of view can significantly improve accuracy.

Abstract

We systematically investigate the error sources for high-precision astrometry from adaptive optics based near-infrared imaging data. We focus on the application in the crowded stellar field in the Galactic Center. We show that at the level of <=100 micro-arcseconds a number of effects are limiting the accuracy. Most important are the imperfectly subtracted seeing halos of neighboring stars, residual image distortions and unrecognized confusion of the target source with fainter sources in the background. Further contributors to the error budget are the uncertainty in estimating the point spread function, the signal-to-noise ratio induced statistical uncertainty, coordinate transformation errors, the chromaticity of refraction in Earth's atmosphere, the post adaptive optics differential tilt jitter and anisoplanatism. For stars as bright as mK=14, residual image distortions limit the astrometry, for fainter stars the limitation is set by the seeing halos of the surrounding stars. In order to improve the astrometry substantially at the current generation of telescopes, an adaptive optics system with high performance and weak seeing halos over a relatively small field (r<=3") is suited best. Furthermore, techniques to estimate or reconstruct the seeing halo could be promising.