原恒星坍缩过程中简单分子的时间演化
Time evolution of simple molecules during proto-star collapse
摘要：
我们研究的形成和演化的几个分子在一个崩溃的星际云使用一个相当大的反应网络包含超过四百个原子和分子物种。我们采用了一个随时间变化的，球对称的，流体动力学代码遵循的流体动力学和化学演化的崩溃云。流动被假定为自引力。我们使用两个模型来研究流体动力学演化：在第一个模型中，我们将物质注入到最初的低密度区域，在第二个模型中，我们从一个恒定密度的云开始，让它由于自引力而崩溃。我们研究了这两种情况下的中央核心的演变。在计算分子氢的形成过程中，我们考虑了颗粒化学的影响，并在每个时间步上进行了气体和颗粒化学的计算。我们遵循的崩溃超过$10^{14}$ s（约300万年），并提出了全球平均丰度的各种简单的，但生物学上重要的分子，如甘氨酸，丙氨酸等的时间演变，我们比较我们的结果与那些从观察中发现，对于较轻的分子的协议一般是非常好的。对于复杂分子，我们倾向于低估丰度。这表明可能存在其他途径来形成这些分子或需要更准确的反应速率。关键词：流体动力学;恒星形成; ISM;化学演化
英文摘要：
We study the formation and evolution of several molecules in a collapsing interstellar cloud using a reasonably large reaction network containing more then four hundred atomic and molecular species. We employ a time dependent, spherically symmetric, hydrodynamics code to follow the hydrodynamic and chemical evolution of the collapsing cloud. The flow is assumed to be self-gravitating. We use two models to study the hydrodynamic evolution: in the first model, we inject matter into an initially low density region and in the second model, we start with a constant density cloud and let it collapse due to self-gravity. We study the evolution of the central core for both the cases. We include the grain chemistry to compute the formation of molecular hydrogen and carried out the effect of gas and grain chemistry at each time step. We follow the collapse for more than $10^{14}$s (about 3 million years) and present the time evolution of the globally averaged abundances of various simple but biologically important molecules, such as glycine, alanine etc. We compare our results with those obtained from observations found that for lighter molecules the agreement is generally very good. For complex molecules we tend to under predict the abundances. This indicates that other pathways could be present to form these molecules or more accurate reaction rates were needed. Keywords: hydrodynamics; star formation; ISM; chemical evolution
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