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Arxiv: JWST Observations of Young protoStars (JOYS). Overview of gaseous molecular emission and absorption in low-mass protostars Published: 10/2/2024 6:08:02 PM Updated: 10/2/2024 6:08:02 PM
Paper abstract: The MIRI-MRS instrument onboard JWST allows for probing the molecular gascomposition at mid-IR wavelengths at unprecedented resolution and sensitivity.It is important to study these features in low-mass embedded protostellarsystems since the formation of planets is thought to start in this phase. Wepresent JWST/MIRI-MRS data of 18 low-mass protostellar systems in the JOYSprogram, focusing on gas-phase molecular lines in spectra extracted from thecentral protostellar positions. Besides H2, the most commonly detectedmolecules are H2O, CO2, CO, and OH. Other molecules such as 13CO2, C2H2, 13CCH,HCN, C4H2, CH4, and SO2 are detected only toward at most three of the sources.The JOYS data also yield the surprising detection of SiO gas toward two sources(BHR71-IRS1, L1448-mm) and for the first time CS and NH3 at mid-IR wavelengthstoward a low-mass protostar (B1-c). The temperatures derived for the majorityof the molecules are 100-300 K, much lower than what is typically derivedtoward more evolved Class II sources (>500 K). Toward three sources (e.g.,TMC1-W), hot (~1000 K) H2O is detected, indicative of the presence of hotmolecular gas in the embedded disks, but such warm emission from othermolecules is absent. The agreement in abundance ratios with respect to H2Obetween ice and gas point toward ice sublimation in a hot core for a fewsources (e.g., B1-c) whereas their disagreement and velocity offsets hint athigh-temperature (shocked) conditions toward other sources (e.g., L1448-mm,BHR71-IRS1). The typical temperatures of the gas-phase molecules of 100-300 Kare consistent with both ice sublimation in hot cores as well ashigh-temperature gas phase chemistry. Molecular features originating from theinner embedded disks are not commonly detected, likely because they are tooextincted even at mid-IR wavelengths by small not-settled dust grains in upperlayers of the disk.