Pinpointing the near-infrared location of Sgr A* by correcting optical distortion in the NACO imager

TL;DR

This paper enhances the astrometric precision of Sgr A*'s location in near-infrared observations by correcting optical distortions in the VLT/NACO imager, enabling more accurate studies of stellar orbits around the Galactic Center.

Contribution

The authors developed a method to model and correct optical distortion in the NACO imager, significantly improving the stability and accuracy of the Sgr A* reference frame.

Findings

Astrometric accuracy improved to ~0.17 mas in position.

Reference frame stability enhanced to ~0.07 mas/yr.

Long-term measurements now span over a decade.

Abstract

Near-infrared observations of stellar orbits at the Galactic Center provide conclusive evidence for a massive black hole associated with the compact radio source Sgr A*. The astrometric reference frame for these observations is tied to a set of red giant stars, which are also detectable at radio wavelengths through SiO maser emission in their envelopes. We have improved the precision and long-term stability of this reference frame, in which Sgr A* is localized to within a factor 5 better than previously: ~0.17 mas in position (in 2009) and ~0.07 mas/yr in velocity. This improvement is the result of modeling and correcting optical distortion in the VLT/NACO imager to a sub-mas level and including new infrared and radio measurements, which now both span more than a decade in time. A further improvement will follow future observations and facilitate the detection of relativistic orbital effects.