3D Kinematics of Stellar SiO Masers in the Galactic Center

Abstract

We present 3D velocity measurements and acceleration limits for stars within a few parsec of the Galactic Center (GC) black hole, Sgr A*, based on observations of 43 and 86 GHz circumstellar maser emission. Observations were taken with the Very Large Array in 2013, 2014, and 2020 and with the Atacama Large Millimeter/submillimeter Array in 2015 and 2017. We detect 28 masers in total, of which four are new detections. Combining these data with extant maser astrometry, we calculate stellar proper motions and accelerations with uncertainties as low as ∼10 μas yr⁻¹ and 0.5 μas yr⁻², respectively, corresponding to approximately 0.5 km s⁻¹ and 0.04 km s⁻¹ yr⁻¹ at a distance of 8 kpc. We measure radial velocities from maser spectra with ∼0.5 km s⁻¹ uncertainties, though the precision and accuracy of such measurements for deducing the underlying stellar velocities are limited by the complex spectral profiles of some masers. We therefore measure radial acceleration limits with typical uncertainties of ∼0.1 km s⁻¹ yr⁻¹. We analyze the resulting 3D velocities and accelerations with respect to expected motions resulting from models of the mass distribution in the GC.