High-resolution SOFIA/EXES Spectroscopy of SO2 Gas in the Massive Young Stellar Object MonR2 IRS3: Implications for the Sulfur Budget

Ryan Dungee; Adwin Boogert; Curtis N DeWitt; Edward Montiel; Matthew J Richter; Andrew G Barr; Geoffrey A Blake; Steven B Charnley; Nick Indriolo; Agata Karska; David A Neufeld; Rachel L Smith; Alexander G G M Tielens

doi:10.3847/2041-8213/aaeda9

High-resolution SOFIA/EXES Spectroscopy of SO₂ Gas in the Massive Young Stellar Object MonR2 IRS3: Implications for the Sulfur Budget

Astrophys J Lett. 2018;868(1):L10. doi: 10.3847/2041-8213/aaeda9. Epub 2018 Nov 16.

Authors

Affiliations

¹ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA; rdungee@hawaii.edu.
² USRA, SOFIA, NASA Ames Research Center, MS 232-11, Moffett Field, CA 94035, USA.
³ Department of Physics, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA.
⁴ Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands.
⁵ Division of Geological and Planetary Sciences, MC 150-21, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, USA.
⁶ Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, USA.
⁷ NASA Goddard Space Flight Center, 8800 Greenbelt Road, MD 20771, USA.
⁸ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA.
⁹ Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland.
¹⁰ Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA.
¹¹ North Carolina Museum of Natural Sciences, 121 West Jones Street, Raleigh, NC 27603, USA.
¹² Department of Physics and Astronomy, Appalachian State University, 525 Rivers Street, Boone, NC 28608-2106, USA.

Abstract

Sulfur has been observed to be severely depleted in dense clouds leading to uncertainty in the molecules that contain it and the chemistry behind their evolution. Here, we aim to shed light on the sulfur chemistry in young stellar objects (YSOs) by using high-resolution infrared spectroscopy of absorption by the ν ₃ rovibrational band of SO₂ obtained with the Echelon-Cross-Echelle Spectrograph on the Stratospheric Observatory for Infrared Astronomy. Using local thermodynamic equilibrium models we derive physical parameters for the SO₂ gas in the massive YSO MonR2 IRS3. This yields a SO₂/H abundance lower limit of 5.6 ± 0.5 × 10^-7, or >4% of the cosmic sulfur budget, and an intrinsic line width (Doppler parameter) of b < 3.20 km s^-1. The small line widths and high temperature (T _ex = 234 ± 15 K) locate the gas in a relatively quiescent region near the YSO, presumably in the hot core where ices have evaporated. This sublimation unlocks a volatile sulfur reservoir (e.g., sulfur allotropes as detected abundantly in comet 67P/Churyumov-Gerasimenko), which is followed by SO₂ formation by warm, dense gas-phase chemistry. The narrowness of the lines makes formation of SO₂ from sulfur sputtered off grains in shocks less likely toward MonR2 IRS3.

Keywords: ISM – ISM; astrochemistry – infrared; individual objects (MonR2 IRS3) – ISM; molecules.

Grants and funding

NNX17AE34G/NASA/United States