2020ApJ...892...52L

Detections of SiO masers from the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey more tightly define the region where Oxygen-rich (O) Asymptotic Giant Branch (AGB) stars reside in multiple infrared (IR) color-color diagrams. Using Midcourse Space eXperiment (MSX) and Two Micron All Sky Survey (2MASS) data along with radio spectra from the BAaDE survey, we find that three main populations were observed in the BAaDE survey: O-rich AGB stars of which about 73% host SiO masers, Carbon-rich (C) AGB stars that do not host these masers, and a small contaminating set of possible Young Stellar Objects (YSOs). The distinction between YSOs and AGB stars can be drawn using only MSX data, specifically the [D]-[E] color, while the shorter wavelengths provided by 2MASS are necessary to divide potential C- and O-rich AGB stars. Divisions similar to these have been seen in multiple earlier IR-studies, but BAaDE currently provides a sample of ∼15,000 sources, which far exceeds previous studies in sample size, and, therefore, provides much more distinct divisions. With these IR distinctions in place, we discuss the sources that are exceptions in either their molecular detections or IR colors, as well as the distribution of the three populations in Galactic coordinates.