Quasi-simultaneous 43 and 86 GHz SiO Maser Observations and Potential Bias in the BAaDE Survey Are Resolved

TL;DR

This study compares SiO maser emissions at 43 and 86 GHz in Mira variables, revealing brightness differences and potential biases in surveys, and discusses implications for understanding circumstellar environments.

Contribution

First simultaneous observations of 43 and 86 GHz SiO masers in a large Mira sample, analyzing line strength ratios and their impact on survey biases and circumstellar conditions.

Findings

43 GHz v=1 line is brighter than 86 GHz v=1 by a factor of 1.36

86 GHz v=1 observations reach 85.9% of the distance compared to 43 GHz

Detection of 43 GHz v=3 line correlates with differences in v=1 line strengths

Abstract

We observed the 43 GHz v=1, 2, and 3 and 86 GHz v=1 SiO maser transitions quasi-simultaneously for a Mira-variable-dominated sample of over 80 sources from the Bulge Asymmetries and Dynamical Evolution (BAaDE) project, using ATCA, and statistically compared the relative line strengths. On average, the 43 GHz v=1 line is brighter than the 86 GHz v=1 line by a factor of 1.36+/-0.15. As a result, an 86 GHz v=1 observed sample can be observed to 85.9% of the distance of a 43 GHz v=1 observed sample using the same sensitivity. We discuss what impact this may have on the BAaDE Galactic plane survey using the VLA and ALMA. Despite fewer v=3 detections, specific trends are discerned or strengthened when the 43 GHz v=3 line is detected. In particular the 43 and 86 GHz v=1 lines are on average equal for sources with no detectable 43 GHz v=3 emission, but the 43 GHz v=1 line strength is on average about twice as bright as the 86 GHz v=1 line for sources with detectable 43 GHz v=3 emission. Some weak correlations are found between line strengths and Midcourse Space Experiment flux densities and colors, which are tightened when considering only sources with detectable 43 GHz v=3 emission. We discuss these trends in the context of a radiative pumping model to highlight how the 43 GHz v=3 line, when coupled with the v=1 and v=2 lines, can further our understanding of variable conditions like density in the circumstellar envelopes.