arXiv 2109.026552021-09astro-ph.GA

星形长丝中低邻对H2比的研究

On the low ortho-to-para H2 ratio in star-forming filaments

Alessandro Lupi, Stefano Bovino, Tommaso Grassi

备注：: 12 pages, 9 figures, 2 tables, matches the published version

摘要：

恒星和行星系统的形成是一个复杂的现象，它依赖于多种物理过程的相互作用。尽管如此，它代表了我们理解宇宙的一个关键阶段，特别是导致彗星和行星上关键分子（例如水）形成的条件。赫歇尔的观测表明，恒星是由气态结构形成的，其中主要成分是分子氢（H $_2$）。根据它的核自旋H $_2$可以以两种形式存在：具有平行自旋的“ortho”和自旋反平行的“para”。这些异构体之间的相对比例，即邻对位比（OPR），在恒星形成气体的热力学和影响分子云中水的氘代的基本化学过程中起着至关重要的作用，通常用于确定太阳系天体中水的起源。在这里，第一次，我们评估的OPR从温暖的中性介质的演变，通过国家的最先进的三维磁流体动力学模拟湍流分子云。我们的研究结果表明，恒星形成云表现出低OPR（$\ll 0.1$）已经在中等密度（$\sim$ 1000厘米$^{-3}$）。我们还限制了宇宙射线电离率，发现$10^{-16}\,\rm s^{-1}$是解释弥散云观测所需的下限。我们的研究结果代表了一个进步的理解恒星和行星形成过程提供了一个强大的确定的化学初始条件的理论和观测研究。

英文摘要：

The formation of stars and planetary systems is a complex phenomenon, which relies on the interplay of multiple physical processes. Nonetheless, it represents a crucial stage for our understanding of the Universe, and in particular of the conditions leading to the formation of key molecules (e.g. water) on comets and planets. Herschel observations demonstrated that stars form out of gaseous filamentary structures in which the main constituent is molecular hydrogen (H$_2$). Depending on its nuclear spin H$_2$ can be found in two forms: `ortho' with parallel spins and `para' where the spins are anti-parallel. The relative ratio among these isomers, i.e. the ortho-to-para ratio (OPR), plays a crucial role in a variety of processes related to the thermodynamics of star-forming gas and to the fundamental chemistry affecting the deuteration of water in molecular clouds, commonly used to determine the origin of water in Solar System's bodies. Here, for the first time, we assess the evolution of the OPR starting from the warm neutral medium, by means of state-of-the-art three-dimensional magneto-hydrodynamic simulations of turbulent molecular clouds. Our results show that star-forming clouds exhibit a low OPR ($\ll 0.1$) already at moderate densities ($\sim$1000 cm$^{-3}$). We also constrain the cosmic rays ionisation rate, finding that $10^{-16}\,\rm s^{-1}$ is the lower limit required to explain the observations of diffuse clouds. Our results represent a step forward in the understanding of the star and planet formation process providing a robust determination of the chemical initial conditions for both theoretical and observational studies.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

摘要：

英文摘要：

相关论文