JWST对大质量原恒星方向上无定形和结晶HDO冰的探测
JWST detections of amorphous and crystalline HDO ice toward massive protostars
AI总结：
本研究利用JWST观测数据量化了两颗原恒星方向冰中的HDO/H$_{2}$O比例，证实大质量热核的气相比例可代表冰相比例，并支持部分CH$_{3}$OH冰在CO冻结前形成。
摘要：
本工作旨在利用JWST提升的灵敏度和分辨率，量化年轻恒星体（YSO）方向冰中的HDO/H$_{2}$O比例，并确定在大质量YSO（MYSO）方向气相中测得的HDO/H$_{2}$O比例是否能代表其冰包层的比例。我们分析了使用JWST NIRSpec在Investigating Protostellar Accretion（IPA）项目中观测的两颗原恒星：HOPS 370，一颗中等质量YSO（IMYSO），以及IRAS 20126+4104，一颗MYSO。这些源的HDO冰在3$\sigma$水平以上被探测到，并通过其4.1 $\mu$m波段进行量化。通过CH$_{3}$OH 3.53 $\mu$m波段限制了CH$_{3}$OH组合模式对该光谱区域观测光深的贡献，以确保HDO特征的积分光深未被高估。H$_{2}$O冰通过其3 $\mu$m波段进行量化。从这些拟合中，HOPS 370和IRAS 20126+4104的冰HDO/H$_{2}$O丰度比分别为4.6$\pm$1.8$\times$10$^{-3}$和2.6$\pm$1.2$\times$10$^{-3}$。同时探测到结晶HDO和结晶H$_{2}$O，证实了将4.1 $\mu$m观测特征归因于HDO冰的判定。冰HDO/H$_{2}$O比例与MYSO方向报告的最高气相HDO/H$_{2}$O比例以及孤立低质量原恒星热内部区域相似，表明大质量热核方向测得的部分气相HDO/H$_{2}$O比例至少能代表冰中的HDO/H$_{2}$O比例。CH$_{3}$OH冰分析中对富H$_{2}$O的CH$_{3}$OH组分的需求，支持了最近的实验和观测结果，即部分CH$_{3}$OH冰可能在CO冻结阶段之前于富H$_{2}$O冰层中形成。
英文摘要：
This work aims to utilize the increased sensitivity and resolution of the JWST 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 phase toward massive YSOs (MYSOs) are representative of the ratios in their ice envelopes. Two protostars observed in the Investigating Protostellar Accretion (IPA) program using JWST NIRSpec were analyzed: HOPS 370, an intermediate-mass YSO (IMYSO), and IRAS 20126+4104, a MYSO. The HDO ice toward these sources was detected above the 3$σ$ level and quantified via its 4.1 $μ$m band. The contributions from the CH$_{3}$OH combination modes to the observed optical depth in this spectral region were constrained via the CH$_{3}$OH 3.53 $μ$m band to ensure that the integrated optical depth of the HDO feature was not overestimated. H$_{2}$O ice was quantified via its 3 $μ$m band. From these fits, ice HDO/H$_{2}$O abundance ratios of 4.6$\pm$1.8$\times$10$^{-3}$ and 2.6$\pm$1.2$\times$10$^{-3}$ are obtained for HOPS 370 and IRAS 20126+4104, respectively. The simultaneous detections of both crystalline HDO and crystalline H$_{2}$O corroborate the assignment of the observed feature at 4.1 $μ$m to HDO ice. The ice HDO/H$_{2}$O ratios are similar to the highest reported gas HDO/H$_{2}$O ratios measured toward MYSOs as well as the hot inner regions of isolated low-mass protostars, suggesting that at least some of the gas HDO/H$_{2}$O ratios measured toward massive hot cores are representative of the HDO/H$_{2}$O ratios in ices. The need for an H$_{2}$O-rich CH$_{3}$OH component in the CH$_{3}$OH ice analysis supports recent experimental and observational results that indicate that some CH$_{3}$OH ice may form prior to the CO freeze-out stage in H$_{2}$O-rich ice layers.
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