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

TL;DR

This paper presents initial results from the BAaDE survey using ALMA, detecting SiO masers in thousands of AGB stars in the Milky Way to study their velocities and distribution.

Contribution

First large-scale ALMA survey of SiO masers in Galactic AGB stars, providing extensive velocity data and insights into stellar populations and maser excitation.

Findings

71% detection rate of SiO masers in infrared-selected sample

Detection rate increases to 80% with MSX color criteria

SiO transitions yield consistent stellar velocities

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.