CHARACTERIZING THE BROWN DWARF FORMATION CHANNELS FROM THE INITIAL MASS FUNCTION AND BINARY-STAR DYNAMICS
CHARACTERIZING THE BROWN DWARF FORMATION CHANNELS FROM THE INITIAL MASS FUNCTION AND BINARY-STAR DYNAMICS
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DOI：
10.1088/0004-637x/800/1/72
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发表时间：
2015-01
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影响因子：
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通讯作者：
I. Thies;J. Pflamm-Altenburg;P. Kroupa;M. Marks
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作者：
I. Thies;J. Pflamm-Altenburg;P. Kroupa;M. Marks
恒星初始质量函数（IMF）是恒星星族的一个重要性质。越来越多的证据表明，通过直接的云碎裂过程的经典恒星形成机制很难再现观测到的棕矮星和极低质量恒星的丰度和双星特性。特别是，最近的恒星IMF的分析推导表现出赤字的棕矮星相比，观测数据。在这里，我们推导出的剩余质量函数的褐矮星作为一个经验措施的褐矮星缺乏在最近的恒星形成模型相对于观测和表明，它是兼容的Thies-Kroupa IMF的亚恒星部分和通过数值模拟获得的质量函数。我们的结论是，现有的模型可以进一步改善，包括一个亚恒星校正项，占额外的形成通道，如磁盘或灯丝碎片。术语“周边破碎”在此被引入用于这种额外的形成通道。此外，我们提出了一个更新的恒星和亚恒星双星的分析模型。由此产生的二进制分数和动态演变的同伴质量比分布是在良好的协议与观测数据的恒星和极低质量的双星在银河系领域，在集群，并在动态未处理的恒星群，如果所有的恒星形成的双星与恒星同伴。对质量函数和伴随质量比分布的正确分析以及结果的解释给出了注意事项。年轻棕矮星周围吸积盘的存在并不意味着它们就像恒星一样直接碎裂。
The stellar initial mass function (IMF) is a key property of stellar populations. There is growing evidence that the classical star-formation mechanism by the direct cloud fragmentation process has difficulties reproducing the observed abundance and binary properties of brown dwarfs and very-low-mass stars. In particular, recent analytical derivations of the stellar IMF exhibit a deficit of brown dwarfs compared to observational data. Here we derive the residual mass function of brown dwarfs as an empirical measure of the brown dwarf deficiency in recent star-formation models with respect to observations and show that it is compatible with the substellar part of the Thies–Kroupa IMF and the mass function obtained by numerical simulations. We conclude that the existing models may be further improved by including a substellar correction term that accounts for additional formation channels like disk or filament fragmentation. The term “peripheral fragmentation” is introduced here for such additional formation channels. In addition, we present an updated analytical model of stellar and substellar binarity. The resulting binary fraction and the dynamically evolved companion mass-ratio distribution are in good agreement with observational data on stellar and very-low-mass binaries in the Galactic field, in clusters, and in dynamically unprocessed groups of stars if all stars form as binaries with stellar companions. Cautionary notes are given on the proper analysis of mass functions and the companion mass-ratio distribution and the interpretation of the results. The existence of accretion disks around young brown dwarfs does not imply that these form just like stars in direct fragmentation.