The Bulge Asymmetries and Dynamical Evolution (BAaDE) SiO Maser Survey at 86 GHz with ALMA

Abstract

We report on the first 1,432 sources observed using the Atacama Large Millimeter/submillimeter Array (ALMA), from the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey, which aims to obtain tens of thousands of line-of-sight velocities from SiO masers in Asymptotic Giant Branch (AGB) stars in the Milky Way. A 71% detection rate of 86 GHz SiO masers is obtained from the infrared color-selected sample, and increases to 80% when considering the likely oxygen-rich stars using Midcourse Space Experiment (MSX) colors isolated in a region where [D]-[E] <= 1.38. Based on Galactic distributions, the presence of extended CS emission, and likely kinematic associations, the population of sources with [D]-[E] > 1.38 probably consists of young stellar objects, or alternatively, planetary nebulae. For the SiO detections we examined whether individual SiO transitions provide comparable stellar line-of-sight velocities, and found that any SiO transition is suitable for determining a stellar AGB line-of-sight velocity. Finally, we discuss the relative SiO detection rates and line strengths in the context of current pumping models.