No CrossRef data available.
Published online by Cambridge University Press: 07 February 2024
Multi-transition SiO maser emission has been detected in over 10 thousand evolved stars across the plane of the Milky Way by the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey. In addition to the large source catalog of the survey, the frequency coverage is also unprecedented: the J=1-0 (43 GHz) data cover seven separate transitions of SiO, and the J=2-1 (86 GHz) data cover ten SiO transitions. In contrast, most other SiO maser data only probe the SiO v=1 and v=2 at 43 GHz and/or the v=1 at 86 GHz. Our extended range allows for the derivation of SiO line ratios for a huge population of evolved stars, including those derived from rare transitions associated with 29SiO and 30SiO isotopologues. We examine how these ratios are affected by the specific combinations of transitions that are detected in a single source. Furthermore, we present a class of ‘isotopologue dominated’ sources where the 29SiO transitions are the brightest in the 43 GHz spectrum. Finally, using Optical Gravitational Lensing Experiment (OGLE) light curves of our maser stars, changes in line ratios as a function of stellar phase are discussed.