Disentangling Confused Stars at the Galactic Center with Long Baseline Infrared Interferometry

TL;DR

This paper uses simulations to demonstrate how infrared interferometry with Keck and VLTI instruments can improve the detection and tracking of stars near Sgr A*, enabling better study of the galactic center's stellar environment.

Contribution

The study shows how dual-field phase referencing enhances confusion noise limits and astrometric precision for observing stars near Sgr A* with current and upcoming interferometers.

Findings

Keck Interferometer can characterize star fields with few bright sources.

GRAVITY can detect and track multiple sources with high precision.

Astrometric monitoring can distinguish relativistic effects and mass distribution around Sgr A*.

Abstract

We present simulations of Keck Interferometer ASTRA and VLTI GRAVITY observations of mock star fields in orbit within ~50 milliarcseconds of Sgr A*. Dual-field phase referencing techniques, as implemented on ASTRA and planned for GRAVITY, will provide the sensitivity to observe Sgr A* with infrared interferometers. Our results show an improvement in the confusion noise limit over current astrometric surveys, opening a window to study stellar sources in the region. Since the Keck Interferometer has only a single baseline, the improvement in the confusion limit depends on source position angles. The GRAVITY instrument will yield a more compact and symmetric PSF, providing an improvement in confusion noise which will not depend as strongly on position angle. Our Keck results show the ability to characterize the star field as containing zero, few, or many bright stellar sources. We are also able to detect and track a source down to mK~18 through the least confused regions of our field of view at a precision of ~200 microarcseconds along the baseline direction. This level of precision improves with source brightness. Our GRAVITY results show the potential to detect and track multiple sources in the field. GRAVITY will perform ~10 microarcsecond astrometry on a mK=16.3 source and ~200 microarcsecond astrometry on a mK=18.8 source in six hours of monitoring a crowded field. Monitoring the orbits of several stars will provide the ability to distinguish between multiple post-Newtonian orbital effects, including those due to an extended mass distribution around Sgr A* and to low-order General Relativistic effects. Early characterizations of the field by ASTRA including the possibility of a precise source detection, could provide valuable information for future GRAVITY implementation and observation.