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arXiv 1409.2242astro-ph.GAastro-ph.SR
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H II区域RCW 82的扩展模型

Model of the expansion of H II region RCW 82

K. V. Krasnobaev, R. R. Tagirova, G. Yu. Kotova

备注：
14 pages, 3 figures
发表信息：
The Astrophysical Journal, Volume 786, Issue 2, article id. 90, 6 pp. (2014)
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摘要：

本文旨在解决在RCW 82 H { \small II}区观测到的年轻天体的形成问题。在一个经典的触发模型的框架中，估计的碎裂时间大于H { \small II}区域的估计年龄。因此，年轻的天体不可能在H { \small II}区域的动力学演化过程中形成。我们提出了一个新的模型，有助于解决这个问题。该模型表明H { \small II}区域RCW 82嵌入在比周围的星际介质更致密的有限尺寸的云中。根据这个模型，当电离激波前沿离开云时，它会导致形成一个加速的致密气体壳层。在加速壳层中，瑞利-泰勒（R-T）不稳定性的影响占主导地位，观测到的约3 pc量级的扰动增长的特征时间为0.14百万年，这小于H { \small II}区域的估计年龄。总时间$t_{\sum}$，即H { \small II}区域到云边缘的膨胀时间、R-T不稳定性增长时间和自由降落时间之和，估计为$0.44<t_{\sum} < 0.78$ Myr。我们的结论是，在H { \small II}区域RCW 82中的年轻天体可能是由于R-T不稳定性而形成的，随后碎裂成大尺度凝聚。

英文摘要：

This paper aims to resolve the problem of formation of young objects observed in the RCW 82 H {\small II} region. In the framework of a classical trigger model the estimated time of fragmentation is larger than the estimated age of the H {\small II} region. Thus the young objects could not have formed during the dynamical evolution of the H {\small II} region. We propose a new model that helps resolve this problem. This model suggests that the H {\small II} region RCW 82 is embedded in a cloud of limited size that is denser than the surrounding interstellar medium. According to this model, when the ionization--shock front leaves the cloud it causes the formation of an accelerating dense gas shell. In the accelerated shell, the effects of the Rayleigh--Taylor (R-T) instability dominate and the characteristic time of the growth of perturbations with the observed magnitude of about 3 pc is 0.14 Myr, which is less than the estimated age of the H {\small II} region. The total time $t_{\sum}$, which is the sum of the expansion time of the H {\small II} region to the edge of the cloud, the time of the R-T instability growth, and the free fall time, is estimated as $0.44<t_{\sum} < 0.78$ Myr. We conclude that the young objects in the H {\small II} region RCW 82 could be formed as a result of the R-T instability with subsequent fragmentation into large-scale condensations.

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