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arXiv 0905.2140astro-ph.GA
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集群中的二进制文件的形成方式与字段中的相同吗?

Do binaries in clusters form in the same way as in the field?

Richard J. Parker, Simon P. Goodwin, Pavel Kroupa, M. B. N. Kouwenhoven

摘要:

我们研究了不同密度星团中双星系统的动力学破坏。我们发现,在高密度(10^4 ~ 10^5 Msun pc^-3)下,几乎所有间隔大于10^3 AU的双星在经过几次穿越后都被摧毁。在低密度(10^2 Msun pc^-3量级)下,许多距离大于10^3 AU的双星被摧毁,而距离大于10^4 AU的双星在经过几次穿越后就没有存活下来。因此,星系团中的双星分离可以作为星系团动力学年龄和过去密度的示踪剂。我们认为,猎户座星云团的中心区域在过去的密度大约是原来的100倍,半质量半径只有0.1 - 0.2 pc,因为(a)它正在膨胀,(b)它只有很少的双星分离> 10^3 AU,(c)它混合良好,因此动力学上很古老。我们还研究了字段二进制人口的起源。距离小于10^2天文单位的双星在任何星团中都不会发生显著的变化,因此在这些距离处,磁场反映了所有恒星形成的总和。距离在10^2 ~ 10^4天文单位范围内的双星,在越来越密集的星团中,受到动力学破裂的影响越来越大。如果大多数恒星的形成都是集群的,那么这些双星相对于磁场来说一定是过度产生的。最后,任何距离大于10^4天文单位的双星都不能在任何星团中存活,因此必须由孤立的恒星形成过程产生,但前提是所有孤立的恒星形成过程都产生极宽的双星。

英文摘要:

We examine the dynamical destruction of binary systems in star clusters of different densities. We find that at high densities (10^4 - 10^5 Msun pc^-3) almost all binaries with separations > 10^3 AU are destroyed after a few crossing times. At low densities (order(10^2) Msun pc^-3) many binaries with separations > 10^3 AU are destroyed, and no binaries with separations > 10^4 AU survive after a few crossing times. Therefore the binary separations in clusters can be used as a tracer of the dynamical age and past density of a cluster. We argue that the central region of the Orion Nebula Cluster was around 100 times denser in the past with a half-mass radius of only 0.1 - 0.2 pc as (a) it is expanding, (b) it has very few binaries with separations > 10^3 AU, and (c) it is well-mixed and therefore dynamically old. We also examine the origin of the field binary population. Binaries with separations < 10^2 AU are not significantly modified in any cluster, therefore at these separations the field reflects the sum of all star formation. Binaries with separations in the range 10^2 - 10^4 AU are progressively more and more heavily affected by dynamical disruption in increasingly dense clusters. If most star formation is clustered, these binaries must be over-produced relative to the field. Finally, no binary with a separation > 10^4 AU can survive in any cluster and so must be produced by isolated star formation, but only if all isolated star formation produces extremely wide binaries.

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