发表机构
European Southern Observatory; Institut de Recherche en Astrophysique et Planétologie; Université de Toulouse; CNRS; CNES; Niels Bohr Institute; University of Copenhagen; Max-Planck-Institut für Radioastronomie; National Radio Astronomy Observatory; Univ. Grenoble Alpes; IPAG; National Tsinghua University; Physikalisch-Meteorologisches Observatorium Davos und Weltstrahlungszentrum (PMOD/WRC); Universität Bern; Seoul National University（欧洲南方天文台; 天体物理与行星学研究所; 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; 尼尔斯·玻尔研究所; 哥本哈根大学; 马克斯·普朗克射电天文学研究所; 美国国家射电天文台; 格勒诺布尔阿尔卑斯大学; 格勒诺布尔天体物理与行星学研究所; 国立清华大学; 达沃斯物理气象观测站暨世界辐射中心; 伯尔尼大学; 首尔国立大学）
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 COMPASS巡天数据，在BHR71-IRS1中探测到多种甲基氰同位素体，通过柱密度比分析，发现其氘化程度与甲醇相似，表明两者形成于相同的星前阶段，且氘化同位素体形成更晚。
AI 中文摘要
甲基氰是在低质量和高质量原恒星周围的气相中观测到的最丰富的含氮复杂有机分子之一。然而，目前很少有观测具有足够宽的频率覆盖范围和足够高的灵敏度，能够系统地表征朝向此类区域的其微量同位素体。我们通过分析作为原恒星中的复杂有机分子：ALMA光谱巡天（COMPASS）大计划一部分的朝向BHR71-IRS1的数据，在约33 GHz频率范围内增加了这一数量。我们研究了朝向BHR71-IRS1的尽可能多的甲基氰同位素体。我们通过光谱拟合并假设局部热力学平衡，得到了柱密度和激发温度。然后我们将导出的柱密度比与朝向IRAS 16293-2422 A和B、V883 Ori、G31.41+0.31和Sgr B2(N2b)的柱密度比进行了比较。我们探测到CH3CN、CH3CN $v_8$=1、13-CH3CN、CH3-13-CN、CH3C-15-N、CH2DCN和CHD2CN。13-CH3CN/CH3-13-CN的柱密度比约为1，与之前的观测一致。CH2DCN/CH3CN的比值对于所有低质量天体都是相似的，但比朝向Sgr B2(N2b)的比值高约一个数量级。这可能是由于更温暖的星前阶段或Sgr B2(N2b)不同的形成时间尺度。从甲基氰同位素体得到的D/H比值与朝向BHR71-IRS1的甲醇的D/H比值很好地吻合，这可能表明甲基氰的形成和氘化发生在与甲醇相似的恒星形成阶段（即星前阶段）。我们发现甲基氰的D/H比值随着氘原子数量的增加而增加，这表明氘化同位素体可能在星前阶段的后期形成。未来的COMPASS研究将增加具有甲基氰分析的低质量系统的样本量，并可能统计性地检验这里观察到的一些趋势。
英文摘要
Methyl cyanide is one of the most abundant nitrogen-bearing complex organic molecules observed in the gas phase around low- and high-mass protostars. However, very few observations exist with a broad enough frequency coverage and sufficiently high sensitivity to systematically characterize its minor isotopologues toward such regions. We add to this number by analyzing data toward BHR71-IRS1 taken as part of the Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) Large Program over a ~33 GHz frequency range. We studied as many isotopologues of methyl cyanide as possible toward BHR71-IRS1. We found the column densities and excitation temperatures via spectral fitting and assuming local thermodynamic equilibrium. We then compared the derived column density ratios with those toward IRAS 16293-2422 A and B, V883 Ori, G31.41+0.31, and Sgr B2(N2b). We detect CH3CN, CH3CN $v_8$=1, 13-CH3CN, CH3-13-CN, CH3C-15-N, CH2DCN, and CHD2CN. The column density ratio of 13-CH3CN/CH3-13-CN is around unity, in agreement with previous observations. The CH2DCN/CH3CN ratios are similar for all the low-mass objects but are ~1 order of magnitude higher than those toward Sgr B2(N2b). This could be due to a warmer pre-stellar phase or a different formation timescale of Sgr B2(N2b). The D/H ratios found from methyl cyanide isotopologues agree well with those of methanol toward BHR71-IRS1, likely pointing to the formation and deuteration of methyl cyanide in a similar star-formation phase as methanol (i.e., the pre-stellar phase). We find an increase in the methyl cyanide D/H ratios with the number of deuterium atoms, which suggests that the deuterated isotopologues may form later in the pre-stellar phase. Future COMPASS studies will increase the sample size of low-mass systems with methyl cyanide analysis and potentially examine some of the trends observed here statistically.
CommentsPublished in A&A, Volume 714, A52
