arXiv 1802.025902018-02-07astro-ph.EPastro-ph.GAastro-ph.SR

解锁原行星盘I中的CO耗尽。温暖的分子层

Unlocking CO Depletion in Protoplanetary Disks I. The Warm Molecular Layer

Kamber R. Schwarz, Edwin A. Bergin, L. Ilsedore Cleeves, Ke Zhang, Karin I. Öberg, Geoffrey A. Blake, Dana Anderson

备注：: 23 pages, 25 figures, 5 tables, accepted for publication in ApJ
DOI：: 10.3847/1538-4357/aaae08

摘要：

CO通常被用作星际介质和原行星盘中总气体质量的示踪剂。最近有很多关于CO作为质量示踪剂在磁盘中的效用的争论。对原行星盘中CO的观测揭示了一系列的CO丰度，在许多系统中测量到低的CO与尘埃质量比。一种可能性是通过化学方法从CO中除去碳。然而，对有利于这种化学后处理的各种物理条件并不十分了解。我们对198个不同物理条件下的原行星盘中的含时化学进行了系统的研究。我们改变尘埃粒度分布，温度，漫画射线和X射线电离率，磁盘质量，和初始水丰度，详细说明什么样的物理条件是必要的激活各种CO消耗机制在温暖的分子层。我们把我们的分析集中在两个区域的温暖分子层：外盘（100 AU）以及CO雪线和内盘（19 AU）内的中面CO雪线。经过一百万年，我们发现，大多数模型有一个CO丰度相对于H $_2$小于$10^{-4}$在外盘，而丰度小于$10^{-5}$需要存在的宇宙射线。在CO雪线内部，CO的显著消耗仅发生在具有高宇宙射线率的模型中。如果宇宙射线不存在于年轻的磁盘，它是很难从CO化学去除碳。此外，去除水之前，CO耗尽阻碍了化学处理的CO。化学处理本身不能解释目前的观测低CO丰度。其他机制也必须参与。

英文摘要：

CO is commonly used as a tracer of the total gas mass in both the interstellar medium and in protoplanetary disks. Recently there has been much debate about the utility of CO as a mass tracer in disks. Observations of CO in protoplanetary disks reveal a range of CO abundances, with measurements of low CO to dust mass ratios in numerous systems. One possibility is that carbon is removed from CO via chemistry. However, the full range of physical conditions conducive to this chemical reprocessing is not well understood. We perform a systematic survey of the time dependent chemistry in protoplanetary disks for 198 models with a range of physical conditions. We varying dust grain size distribution, temperature, comic ray and X-ray ionization rate, disk mass, and initial water abundance, detailing what physical conditions are necessary to activate the various CO depletion mechanisms in the warm molecular layer. We focus our analysis on the warm molecular layer in two regions: the outer disk (100 au) well outside the CO snowline and the inner disk (19 au) just inside the midplane CO snow line. After 1 Myr, we find that the majority of models have a CO abundance relative to H$_2$ less than $10^{-4}$ in the outer disk, while an abundance less than $10^{-5}$ requires the presence of cosmic rays. Inside the CO snow line, significant depletion of CO only occurs in models with a high cosmic ray rate. If cosmic rays are not present in young disks it is difficult to chemically remove carbon from CO. Additionally, removing water prior to CO depletion impedes the chemical processing of CO. Chemical processing alone cannot explain current observations of low CO abundances. Other mechanisms must also be involved.

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