CO J = 2 - 1 Emission from Evolved Stars in the Galactic Bulge

TL;DR

This study detects CO J=2-1 emission from three evolved stars in the Galactic Bulge, estimating their gas mass-loss rates and gas-to-dust ratios, and highlights challenges due to foreground contamination.

Contribution

First detection of CO J=2-1 emission from evolved stars in the Galactic Bulge with derived mass-loss rates and gas-to-dust ratios, advancing understanding of stellar evolution in this region.

Findings

Detected CO J=2-1 emission from 3 stars in the Galactic Bulge.

Estimated gas mass-loss rates ranging from 3.4 to 7.9 x 10^-5 M_Sun/year.

Determined gas-to-dust ratios between 160 and 310.

Abstract

We observe a sample of 8 evolved stars in the Galactic Bulge in the CO J = 2 - 1 line using the Submillimeter Array (SMA) with angular resolution of 1 - 4 arcseconds. These stars have been detected previously at infrared wavelengths, and several of them have OH maser emission. We detect CO J = 2 - 1 emission from three of the sources in the sample: OH 359.943 +0.260, [SLO2003] A12, and [SLO2003] A51. We do not detect the remaining 5 stars in the sample because of heavy contamination from the galactic foreground CO emission. Combining CO data with observations at infrared wavelengths constraining dust mass loss from these stars, we determine the gas-to-dust ratios of the Galactic Bulge stars for which CO emission is detected. For OH 359.943 +0.260, we determine a gas mass-loss rate of 7.9 (+/- 2.2) x 10^-5 M_Sun/year and a gas-to-dust ratio of 310 (+/- 89). For [SLO2003] A12, we find a gas mass-loss rate of 5.4 (+/- 2.8) x 10^-5 M_Sun/year and a gas-to-dust ratio of 220 (+/- 110). For [SLO2003] A51, we find a gas mass-loss rate of 3.4 (+/- 3.0) x 10^-5 M_Sun/year and a gas-to-dust ratio of 160 (+/- 140), reflecting the low quality of our tentative detection of the CO J = 2 - 1 emission from A51. We find the CO J = 2 - 1 detections of OH/IR stars in the Galactic Bulge require lower average CO J = 2 - 1 backgrounds.