发表机构
INAF - Osservatorio Astrofisico di Arcetri; Observatoire de Paris; PSL Research University; CNRS; Vrije Universiteit Amsterdam（意大利国家天体物理研究所-阿尔切特里天体物理天文台; 巴黎天文台; 巴黎文理研究大学; 法国国家科学研究中心; 阿姆斯特丹自由大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过CHEMICO项目观测大质量恒星形成核中的分子离子，发现含硫离子及N2D+、DCO+、SO+丰度是灵敏的演化示踪剂，并测得随演化增高的宇宙射线电离率。
AI 中文摘要
分子离子在星际介质中分子的形成过程中起着启动和调控的关键作用，并被认为是恒星形成区域演化的灵敏示踪剂。在“大质量恒星形成核中的化学演化”（CHEMICO）项目框架内，我们研究了朝向三个代表连续演化阶段的大质量恒星形成核的分子离子的时间演化。CHEMICO基于利用毫米波射电天文研究所30米望远镜进行的3毫米、2毫米和1.2毫米波段的无偏谱线巡天。我们探测到19种分子离子，包括同位素取代体。通过局部热动平衡分析，我们得出以下主要结果：（i）总体而言，含硫离子的物理参数对演化最敏感，而含氮离子的物理参数最不敏感；（ii）表现出最显著时间变化的分子丰度是SO+、DCO+和N2D+；（iii）一种针对暖气体条件定制的简单解析方法给出的H2宇宙射线电离率比星际介质中测量的典型值高出几个数量级，并随演化显著增加；（iv）质子化物种与中性物种的丰度比随着中性物种的质子亲和能的增加而增加，无论源处于何种演化阶段，这表明质子转移在冷和暖星际环境中似乎以相似的方式进行。分子离子在大质量恒星形成区域表现出不同的演化趋势，其中含硫物种以及N2D+、DCO+和SO+的丰度成为特别灵敏的演化示踪剂。测量的电子丰度和宇宙射线电离率与内部产生宇宙射线且其效率随时间增加的情况一致。
英文摘要
Molecular ions are crucial in initiating and regulating the formation of molecules in the interstellar medium, and are expected to be sensitive tracers of evolution in star-forming regions. Within the framework of the project `CHemical Evolution of MassIve star-forming COres' (CHEMICO), we investigate the temporal evolution of molecular ions towards three high-mass star-forming cores that represent three sequential evolutionary stages. CHEMICO is based on an unbiased spectral line survey of the bandwidth at 3, 2, and 1.2~mm carried out with the 30m telescope of the Insitut de Radioastronomie millimétrique. We detect 19 molecular ions, including isotopologues. From a local thermodynamic equilibrium analysis, we derive the following main results: (i) Overall, the physical parameters of sulphur-bearing ions are the most sensitive to evolution, whereas those of nitrogen-bearing ions are the least; (ii) The molecular abundances that exhibit the most pronounced temporal variations are those of SO+, DCO+, and N2D+; (iii) A simple analytic approach tailored for warm gas conditions provides cosmic-ray ionisation rates of H2 several orders of magnitude above the canonical values measured in the interstellar medium and with a marked increase with evolution; (iv) The abundance ratio of protonated-to-neutral species increases with the proton affinity of the neutral regardless of the evolutionary stage of the source, indicating that proton-transfer appears to proceed similarly in both cold and warm interstellar environments. Molecular ions exhibit distinct evolutionary trends in high-mass star-forming regions, with sulphur-bearing species and the abundances of N2D+, DCO+, and SO+ emerging as particularly sensitive tracers of evolution. Measured electron fractions and cosmic-ray ionisation rates are in line with an internal production of cosmic-rays that becomes increasingly efficient with time.
Comments20 pages, 6 figures, 6 tables, 4 Appendices
