ALMA-PILS调查：第一次检测到不饱和3碳分子普罗芬（C $_2$ H $_3$ CHO）和丙烯（C $_3$ H $_6$）（IRAS 16293 $-$ 2422 B）
The ALMA-PILS survey: First detection of the unsaturated 3-carbon molecules Propenal (C$_2$H$_3$CHO) and Propylene (C$_3$H$_6$) towards IRAS 16293$-$2422 B
摘要：
含有三个碳原子的复杂有机分子在恒星形成的最早阶段被发现。特别地，丙烯醛（C $_2$ H $_3$ CHO）是感兴趣的物种，因为其在更复杂的物种甚至生物分子的形成中的含义。本研究旨在寻找低质量原恒星双星IRAS 16293- 2422的热科里诺区是否存在C $_2$ H $_3$ CHO和丙烯（C $_3$ H $_6$）等三碳物种，以了解它们的形成途径。我们利用ALMA在波段6和波段7的观测资料，在原恒星IRAS 16293- 2422 B（IRAS 16293 B）中寻找C $_3$ H $_6$和C $_2$ H $_3$ CHO的存在。我们报告了对IRAS 16293 B的C $_3$ H $_6$和C $_2$ H $_3$ CHO的检测，然而，未发现对二元系统的另一个组分IRAS 16293 A的未混合线。我们推导出C-$_3$ H $_8$、HCCCHO、n-C-$_3$ H $_7$ OH、i-C-$_3$ H $_7$ OH、C-$_3$ O和顺式-HC（O）CHO对IRAS 16293 B的柱密度上限。然后，我们使用一个三相化学模型来模拟这些物种的形成在一个典型的星前环境，然后其流体力学崩溃，直到中央原恒星的诞生。不同的形成路径，如连续氢化和自由基，自由基添加在晶粒表面，进行了测试和比较的观测结果。模拟再现了与针对IRAS 16293 B观察到的丰度在一个数量级内的丰度，对于气相反应C PDMATHAMN + O $\rightarrow$ C PDMATHAMM + CO的$10^{-12}$ cm $^3$ s $^{-1}$的速率发现了最佳的一致性。和CH $_3$ OCHO是复杂有机分子的主要和关键的形成途径，而连续的氢化途径和自由基-自由基加成反应都有助于C $_2$ H $_5$ CHO的形成。
英文摘要：
Complex organic molecules with three carbon atoms are found in the earliest stages of star formation. In particular, propenal (C$_2$H$_3$CHO) is a species of interest due to its implication in the formation of more complex species and even biotic molecules. This study aims to search for the presence of C$_2$H$_3$CHO and other three-carbon species such as propylene (C$_3$H$_6$) in the hot corino region of the low-mass protostellar binary IRAS 16293--2422 to understand their formation pathways. We use ALMA observations in Band 6 and 7 from various surveys to search for the presence of C$_3$H$_6$ and C$_2$H$_3$CHO towards the protostar IRAS 16293--2422 B (IRAS 16293B). We report the detection of both C$_3$H$_6$ and C$_2$H$_3$CHO towards IRAS 16293B, however, no unblended lines were found towards the other component of the binary system, IRAS 16293A. We derive column density upper limits for C$_3$H$_8$, HCCCHO, n-C$_3$H$_7$OH, i-C$_3$H$_7$OH, C$_3$O, and cis-HC(O)CHO towards IRAS 16293B. We then use a three-phase chemical model to simulate the formation of these species in a typical prestellar environment followed by its hydrodynamical collapse until the birth of the central protostar. Different formation paths, such as successive hydrogenation and radical-radical additions on grain surfaces, are tested and compared to the observational results. The simulations reproduce the abundances within one order of magnitude from those observed towards IRAS 16293B, with the best agreement found for a rate of $10^{-12}$ cm$^3$ s$^{-1}$ for the gas-phase reaction C$_3$ + O $\rightarrow$ C$_2$ + CO. Successive hydrogenations of C$_3$, HC(O)CHO, and CH$_3$OCHO on grain surfaces are a major and crucial formation route of complex organics molecules, whereas both successive hydrogenation pathways and radical-radical addition reactions contribute to the formation of C$_2$H$_5$CHO.
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