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arXiv 0906.0584astro-ph.SR
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年轻恒星天体的化学模拟。方法和基准

Chemical Modelling of Young Stellar Objects, I. Method and Benchmarks

Simon Bruderer, Steven D. Doty, Arnold O. Benz

备注：
Accepted by ApJS. 24 pages, 15 figures. A version with higher resolution images is available from http://www.astro.phys.ethz.ch/staff/simonbr/papgridI.pdf . Online data available at http://www.astro.phys.ethz.ch/chemgrid.html . Second paper of this series of papers available at arXiv:0906.0588
发表信息：
Astrophys.J.Supp.183:179-196,2009
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摘要：

即将到来的设施，如赫歇尔空间天文台或ALMA将提供丰富的年轻恒星物体（YSO）的分子线观测。根据线通量，可以通过辐射转移计算来估计化学丰度。为了从丰度中推导出物理性质，需要对化学网络进行建模，并将其与观测结果进行拟合。然而，该建模过程在计算上要求极高，特别是如果除了密度和温度之外，还必须考虑远紫外（FUV）照射、X射线和多维几何形状。我们开发了一个快速的工具，适用于各种应用程序的化学建模在YSO。具有密度、温度、FUV辐射和X射线通量的气体的化学组成的网格被预先计算为时间的函数。一个特定的插值方法的开发，以减少数据库到一个可行的大小。已发表的AFGL 2591模型被用来验证该方法的准确性。对FUV敏感分子进行第二个基准测试。化学建模的新方法比直接建模快250，000倍以上，平均因子为1.35。该工具已分发供公众使用。在方法的发展过程中，我们对化学演化进行了探索：我们发现，通过提高宇宙射线电离率，可以再现YSO包层中的X射线化学。我们进一步发现，在低密度气体与高电离的CH+的丰度可以通过双电离的碳（C++）的重组，并提出了一个新的值的初始丰度的主要硫载流子在热的核心。

英文摘要：

Upcoming facilities such as the Herschel Space Observatory or ALMA will deliver a wealth of molecular line observations of young stellar objects (YSOs). Based on line fluxes, chemical abundances can then be estimated by radiative transfer calculations. To derive physical properties from abundances, the chemical network needs to be modeled and fitted to the observations. This modeling process is however computationally exceedingly demanding, particularly if in addition to density and temperature, far UV (FUV) irradiation, X-rays, and multi-dimensional geometry have to be considered. We develop a fast tool, suitable for various applications of chemical modeling in YSOs. A grid of the chemical composition of the gas having a density, temperature, FUV irradiation and X-ray flux is pre-calculated as a function of time. A specific interpolation approach is developed to reduce the database to a feasible size. Published models of AFGL 2591 are used to verify the accuracy of the method. A second benchmark test is carried out for FUV sensitive molecules. The novel method for chemical modeling is more than 250,000 times faster than direct modeling and agrees within a mean factor of 1.35. The tool is distributed for public use. In the course of devloping the method, the chemical evolution is explored: We find that X-ray chemistry in envelopes of YSOs can be reproduced by means of an enhanced cosmic-ray ionization rate. We further find that the abundance of CH+ in low-density gas with high ionization can be enhanced by the recombination of doubly ionized carbon (C++) and suggest a new value for the initial abundance of the main sulphur carrier in the hot-core.

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