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

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 SO 2 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 SO 2 gas in the massive YSO MonR2 IRS3. This yields a SO 2 /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 SO 2 formation by warm, dense gas-phase chemistry. The narrowness of the lines makes formation of SO 2 from sulfur sputtered off grains in shocks less likely toward MonR2 IRS3.

The First Mid-infrared Detection of HNC in the Interstellar Medium: Probing the Extreme Environment toward the Orion Hot Core

“…Similar to our conclusion, Barr et al (2020) find that the MIR probes hot gas at the center of hot cores, compared to the sub-millimeter which probes the outer envelope. Two previous studies also show that SOFIA/EXES detects molecules previously unobserved at longer wavelengths (Barr et al 2018;Dungee et al 2018).…”

“…Currently, this is the only spectrograph able to resolve individual molecular transitions over the entire MIR. Several studies of hot cores with SOFIA/ EXES are ongoing (Indriolo et al 2015a(Indriolo et al , 2020Barr et al 2018Barr et al , 2020Dungee et al 2018). Rangwala et al (2018) detected eight HCN R-branch rovibrational transitions toward IRc2 between 12.96 and 13.33 μm, enough to directly calculate its temperature and column density.…”

Efficient Production of S8 in Interstellar Ices: The Effects of Cosmic-Ray-driven Radiation Chemistry and Nondiffusive Bulk Reactions

“…The recent detection of several new sulfur-bearing molecules in the interstellar medium (ISM) (Agundez et al 2018;Cernicharo et al 2018), as well as in comet 67P/Churyumov-Gerasimenko (67P/C-G) by the Rosetta orbiter (Calmonte et al 2016) has, in part, spurred renewed interest in the chemistry of this malodorous element (Hudson & Gerakines 2018;Morgan et al 2018;Dungee et al 2018;Danilovich et al 2018;Drozdovskaya et al 2018;Zakharenko et al 2019;Gorai et al 2017).…”

High Resolution Infrared Spectroscopy of Hot Molecular Gas in AFGL 2591 and AFGL 2136: Accretion in the Inner Regions of Disks Around Massive Young Stellar Objects

“…This study focuses on AFGL 2136 and AFGL 2591, however several other hot cores have been observed before at high spectral resolution at MIR wavelengths using a few specifically chosen settings. These studies reveal MIR transitions in absorption towards hot cores (Mitchell et al 1989(Mitchell et al , 1990Evans et al 1991;Knez et al 2009;Barentine & Lacy 2012;Rangwala et al 2018;Dungee et al 2018;Indriolo et al 2013Indriolo et al , 2015Indriolo et al , 2020. Hot cores have also been observed at low spectral resolution in the MIR with ISO (Lahuis & van Dishoeck 2000;Keane et al 2001;.…”