FAUST X：原双星系统[BHB2007] 11中的甲醛：小尺度氘化
FAUST X: Formaldehyde in the Protobinary System [BHB2007] 11: Small Scale Deuteration
AI总结：
基于FAUST项目，利用ALMA首次研究原双星系统[BHB2007] 11的甲醛氘化，测定了各同位素体柱密度与D/H比，并发现由宽角盘风驱动的非对称分子外流。
摘要：
背景。在恒星形成的早期阶段，含氢（H）物种中的氘（D）会得到富集，然而，目前仅有少量针对原恒星天体的高空间分辨率氘化研究，导致小尺度结构尚未被揭示和研究不足。目标。我们旨在约束甲醛（H2CO）中0/I类原恒星天体的氘同位素分馏比，甲醛在此环境中具有丰富的氘化同位素体。方法。我们在大型项目FAUST框架内使用ALMA观测了0/I类原双星系统[BHB2007] 11，其辐射分量嵌于半径为2-3 au的星周盘中。该系统被连接到更大环双星盘的复杂丝状结构所包围。本工作提出了对该源甲醛D分馏的首次研究，探测到H2CO 3(0,3)-2(0,2)，并结合HDCO 4(2,2)-3(2,1)、HDCO 4(1,4)-3(1,3)和D2CO 4(0,4)-3(0,3)。这些观测使得能够分辨与同样由FAUST数据揭示的甲醇热点相关联的多个速度分量以及外部包层。此外，基于在H2CO辐射观测中看到的运动学，我们提出了存在第二个大尺度外流。结果。HDCO和D2CO仅在核心中心区域被发现，而H2CO的分布更为普遍。从辐射转移建模得出，H2CO、HDCO和D2CO的柱密度范围分别为(3-8)x10$^{14}$ cm$^{-2}$、(0.8-2.9)x10$^{13}$ cm$^{-2}$和(2.6-4.3)x10$^{12}$ cm$^{-2}$，得出平均D/H比为0.01-0.04。根据运动学建模结果，第二个大尺度特征与流线状性质不一致，因此我们初步得出结论，该特征是由宽角盘风驱动的非对称分子外流。
英文摘要：
Context. Deuterium in H-bearing species is enhanced during the early stages of star formation, however, only a small number of high spatial resolution deuteration studies exist towards protostellar objects, leaving the small-scale structures unrevealed and understudied. Aims. We aim to constrain the deuterium fractionation ratios in a Class 0/I protostellar object in formaldehyde (H2CO), which has abundant deuterated isotopologues in this environment. Methods. We observed the Class 0/I protobinary system [BHB2007] 11, whose emission components are embedded in circumstellar disks that have radii of 2-3 au, using ALMA within the context of the Large Program FAUST. The system is surrounded by a complex filamentary structure connecting to the larger circumbinary disk. In this work we present the first study of formaldehyde D-fractionation towards this source with detections of H2CO 3(0,3)-2(0,2), combined with HDCO 4(2,2)-3(2,1), HDCO 4(1,4)-3(1,3) and D2CO 4(0,4)-3(0,3). These observations enable multiple velocity components associated with the methanol hotspots also uncovered by FAUST data, as well as the external envelope, to be resolved. In addition, based on the kinematics seen in the observations of the H2CO emission, we propose the presence of a second large scale outflow. Results. HDCO and D2CO are only found in the central regions of the core while H2CO is found more ubiquitously. From radiative transfer modelling, the column densities ranges found for H2CO, HDCO and D2CO are (3-8)x10$^{14}$ cm$^{-2}$, (0.8-2.9)x10$^{13}$ cm$^{-2}$ and (2.6-4.3)x10$^{12}$ cm$^{-2}$, respectively, yielding an average D/H ratio of 0.01-0.04. Following the results of kinematic modelling, the second large scale feature is inconsistent with a streamer-like nature and we thus tentatively conclude that the feature is an asymmetric molecular outflow launched by a wide-angle disk wind.
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