发表机构
Max-Planck-Institut für Radioastronomie; Max-Planck-Institut für extraterrestrische Physik; Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, CNES; Physikalisch-Meteorologisches Observatorium Davos und Weltstrahlungszentrum (PMOD/WRC); Universität Bern; Niels Bohr Institute, University of Copenhagen; Seoul National University; National Radio Astronomy Observatory; Institute of Astronomy, Department of Physics, National Tsinghua University; Univ. Grenoble Alpes, CNRS, IPAG（马克斯·普朗克射电天文研究所; 马克斯·普朗克地外物理研究所; 图卢兹大学、法国国家科学研究中心、法国国家空间研究中心天体物理学和行星学研究所在; 达沃斯物理气象观测站和世界辐射中心; 伯尔尼大学; 哥本哈根大学尼尔斯·玻尔研究所; 首尔大学; 美国国家射电天文台; 国立清华大学物理系天文学研究所; 格勒诺布尔阿尔卑斯大学、法国国家科学研究中心IPAG）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用ALMA的COMPASS巡天数据，在原恒星IRAS4A2中首次探测到完全氘代甲醇CD3OD，揭示甲醇氘代模式，并指出化学模型无法定量再现该模式，凸显氘分馏作为恒星形成过程诊断工具的价值。
AI 中文摘要
迄今为止，星际介质（ISM）中尚未有完全氘代甲醇CD3OD的可靠鉴定。我们的目标是继续在恒星形成区搜寻CD3OD，以确定甲醇的氘代模式，并为氘代过程设定约束条件。我们使用了阿塔卡马大型毫米/亚毫米波阵列（ALMA）开展的大型项目“原恒星中的复杂有机分子——ALMA光谱巡天（COMPASS）”中，对NGC1333分子云中原恒星系统IRAS4A进行的灵敏成像光谱巡天数据。在局部热力学平衡（LTE）假设下，推导了甲醇及其若干低丰度同位素体（包括氘代同位素体）的柱密度。除了在双星成分IRAS4A2方向探测到多种甲醇同位素体外，我们报告了CD3OD的首次星际探测。IRAS4A2中甲醇的氘代模式与其他低质量原恒星中测量到的模式相似，表观D/H比从单氘代到多氘代同位素体呈增加趋势。针对氘代的化学模型未能定量再现这种模式，而CD3OD的探测使这一差异更加显著。我们的LTE光谱建模得出甲醇与其13C和18O同位素体的柱密度比值较低，而13C与18O以及18O与17O的比值与本地ISM中预期的同位素比值一致。我们怀疑甲醇的柱密度被低估了。一种可能的解释是发射呈团块状而非整体均匀。完全氘代复杂有机分子（COM）的首次探测凸显了氘分馏作为研究恒星形成过程中有机分子形成与继承的诊断工具的强大威力。
英文摘要
There have been no robust identifications of fully deuterated methanol, CD3OD, in the interstellar medium (ISM) to date. Our goal is continue the search for CD3OD in star-forming regions to determine the deuteration pattern of methanol and set constraints on the deuteration process. We used a sensitive imaging spectral survey of the protostellar system IRAS4A in the NGC1333 molecular cloud performed as part of the large program carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) called Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). The column densities of methanol and several of its less abundant isotopologs, including deuterated ones, were derived under the assumption of local thermodynamic equilibrium (LTE). Along with the detection of several methanol isotopologs toward the binary component IRAS4A2, we report the first interstellar detection of CD3OD. The deuteration pattern of methanol in IRAS4A2 is similar to the pattern measured in other low-mass protostars, with an increase in the apparent D/H ratio from the singly to multiply deuterated isotopologs. Chemical models of prestellar and protostellar cores focused on deuteration do not reproduce this pattern quantitatively. This discrepancy is even more exacerbated by the detection of CD3OD. Our LTE modeling of the spectra yields low column density ratios of methanol to its 13C and 18O isotopologs while the 13C to 18O and 18O to 17O ratios are consistent with the isotopic ratios expected in the local ISM. We suspect that the column density of methanol is underestimated. One possible explanation is that the emission is clumpy rather than monolithic. The first detection of a fully deuterated COM highlights the power of deuterium fractionation as a diagnostic tool for investigating the formation and inheritance of organic molecules during the process of star formation.
CommentsAccepted for publication in Astronomy and Astrophysics
