Molecular evolution in collapsing prestellar cores. III. Contraction of a Bonnor-Ebert sphere
Molecular evolution in collapsing prestellar cores. III. Contraction of a Bonnor-Ebert sphere
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DOI：
10.1086/427017
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发表时间：
2005-02-10
影响因子：
4.9
通讯作者：
Caselli, P
中科院分区：
文献类型：
--
作者：
Aikawa, Y;Herbst, E;Caselli, P
用数值计算方法研究了球形云核的引力坍缩。核心的初始条件接近临界Bonnor-Ebert球，在一个模型中（α = 1.1），中心密度类似于10（4）cm（-3），而在另一个模型中（α = 4.0），重力是压力的两倍，其中α是内部重力与压力的比值。α = 1.1的模型显示出合理的协议与所观察到的速度场在星前核。通过求解包含气相反应和颗粒表面反应的化学反应网络，计算了核中的分子分布。当核心的中心密度达到10（5）cm（-3）时，在α = 1.1模型的中心区域中，含碳物种显著地减少，而在另一模型中，减少仅是边际的。这两种不同的方法涵盖了所观察到的分子分布在不同的星前核心的变化，这表明分子分布可以探针的收缩或积累的时间尺度的核心。NH3/N2 H+比率的中心增强，这是在一些星前核中观察到的，可以复制在一定条件下，通过采用最近测量的N2 H+重组的分支分数。各种分子物种，如CH 3OH和CO2，通过颗粒表面反应产生。冰的成分对假定的温度有很大的依赖性。多氘物种包括在我们最新的气体-颗粒化学网络中。H-3（+）的氘代同位素异构体可用作演化核中心区域的探针，其中具有重元素的气相物质强烈贫化。在10 K，我们的模型可以重现所观察到的丰度比ND 3/ NH3，但低估了氘代正常甲醇的同位素比。
The gravitational collapse of a spherical cloud core is investigated by numerical calculations. The initial conditions of the core lie close to the critical Bonnor- Ebert sphere with a central density of similar to 10(4) cm(-3) in one model (alpha = 1.1), while gravity overwhelms pressure in the other ( alpha = 4.0), where alpha is the internal gravity- to-pressure ratio. The alpha = 1.1 model shows reasonable agreement with the observed velocity field in prestellar cores. Molecular distributions in cores are calculated by solving a chemical reaction network that includes both gas-phase and grain- surface reactions. When the central density of the core reaches 10(5) cm(-3), carbon- bearing species are significantly depleted in the central region of the alpha = 1.1 model, while the depletion is only marginal in the other model. The two different approaches encompass the observed variations of molecular distributions in different prestellar cores, suggesting that molecular distributions can be probes of contraction or accumulation timescales of cores. The central enhancement of the NH3/ N2H+ ratio, which is observed in some prestellar cores, can be reproduced under certain conditions by adopting recently measured branching fractions for N2H+ recombination. Various molecular species, such as CH3OH and CO2, are produced by grain- surface reactions. The ice composition depends sensitively on the assumed temperature. Multideuterated species are included in our most recent gas- grain chemical network. The deuterated isotopomers of H-3(+) are useful as probes of the central regions of evolved cores, in which gas- phase species with heavy elements are strongly depleted. At 10 K, our model can reproduce the observed abundance ratio of ND3/ NH3 but underestimates the isotopic ratios of deuterated to normal methanol.