The Milky Way Bar Potential Constrained by the Kinematics of SiO Maser Stars in BAaDE Survey

Abstract

We introduce a novel method that utilizes the longitude–velocity (l − v) envelope to constrain the Milky Way (MW) bar potential. Previous work used the l − v diagram to explain the distribution of the observed high-velocity stars. We successfully reproduce their results but find that their method is limited to only one type of periodic orbits. In contrast, we propose that the l − v envelope provides much more comprehensive constraints. We compare the properties of test particles in the M. Portail et al. MW potential model (P17) with the observed SiO maser stars from the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey. We find that the l − v envelope generated by the bar potential demonstrates reasonable agreement with the observational data, albeit with slight discrepancies near the Galactic center. The inconsistencies suggest that the P17 potential yields a lower central rotation curve, a slightly larger quadrupole strength, or a possibly underestimated pattern speed. We also adopt an updated version of the P17 potential with a modified central mass component proposed by G. H. Hunter et al. (H24). The fitting of the l − v envelope suggests that the H24 potential does not completely address the existing challenges and may hint at a possible underestimation of the central bar mass. Our study demonstrates that the l − v envelope can be used as a valuable tool for constraining the Galactic potential and provides insights into the MW bar potential.