Direct measurement of the Galactic bar pattern speed with SiO maser stars

Bar pattern speed is a fundamental parameter of the Milky Way, which could be measured directly from stellar motions in the bar/bulge region, where dust extinction is significant. As an excellent tracer in the bulge, SiO maser stars can provide an unprecedented opportunity to study the dynamics in the bulge region with precise stellar motion. The bulge Asymmetries and Dynamic Evolution (BAaDe) survey observed AGB stars with SiO maser emission with ALMA and VLA. Radio observations of the SiO maser lines yield accurate line-of-sight velocities in regions of galactic bulge and plane, which is not reachable with optical surveys. Using BAaDe dataset, we measure the bar pattern speed with a revised Tremaine-Weinberg method. We also test sample selection effects on the TW method with simulations, and evaluate various systematic errors of this method.