Disentangling confused stars at the galactic center with long-baseline infrared interferometry

We present simulations of Keck Interferometer ASTRA and VLTI GRAVITY observations of mock star fields in orbit within 50mas of SgrA*. Dual-field phase referencing techniques, as implemented on ASTRA and planned for GRAVITY, will provide the sensitivity to observe SgrA* with long-baseline 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 point-spread function, 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 m_K 18 through the least confused regions of our field of view at a precision of 200 μas 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 μas astrometry on an m_K = 16.3 source and 200 μas astrometry on an m_K = 18.8 source in 6 hr 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 SgrA* and to low-order general relativistic effects. ASTRA and GRAVITY both have the potential to detect and monitor sources very close to SgrA*. 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.