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Arxiv: JWST detections of amorphous and crystalline HDO ice toward massive protostars Published: 4/23/2024 9:00:00 PM Updated: 4/23/2024 9:00:00 PM

Paper abstract: This work aims to utilize the increased sensitivity and resolution of theJWST to quantify the HDO/H_{2}O ratio in ices toward young stellar objects(YSOs) and to determine if the HDO/H_{2}O ratios measured in the gas phasetoward massive YSOs (MYSOs) are representative of the ratios in their iceenvelopes. Two protostars observed in the Investigating Protostellar Accretion(IPA) program using JWST NIRSpec were analyzed: HOPS 370, an intermediate-massYSO (IMYSO), and IRAS 20126+4104, a MYSO. The HDO ice toward these sources wasdetected above the 3\sigma level and quantified via its 4.1 \mum band. Thecontributions from the CH_{3}OH combination modes to the observed opticaldepth in this spectral region were constrained via the CH_{3}OH 3.53 \mumband to ensure that the integrated optical depth of the HDO feature was notoverestimated. H_{2}O ice was quantified via its 3 \mum band. From thesefits, ice HDO/H_{2}O abundance ratios of 4.6\pm1.8\times10^{-3} and2.6\pm1.2\times10^{-3} are obtained for HOPS 370 and IRAS 20126+4104,respectively. The simultaneous detections of both crystalline HDO andcrystalline H_{2}O corroborate the assignment of the observed feature at 4.1\mum to HDO ice. The ice HDO/H_{2}O ratios are similar to the highestreported gas HDO/H_{2}O ratios measured toward MYSOs as well as the hot innerregions of isolated low-mass protostars, suggesting that at least some of thegas HDO/H_{2}O ratios measured toward massive hot cores are representative ofthe HDO/H_{2}O ratios in ices. The need for an H_{2}O-rich CH_{3}OHcomponent in the CH_{3}OH ice analysis supports recent experimental andobservational results that indicate that some CH_{3}OH ice may form prior tothe CO freeze-out stage in H_{2}O-rich ice layers.