M-dwarf binaries as tracers of star and brown dwarf formation
M-dwarf binaries as tracers of star and brown dwarf formation
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DOI：
10.1093/mnras/stv1361
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发表时间：
2015-06
影响因子：
4.8
通讯作者：
M. Marks;M. Janson;P. Kroupa;N. Leigh;I. Thies
中科院分区：
文献类型：
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作者：
M. Marks;M. Janson;P. Kroupa;N. Leigh;I. Thies
在AstraLux调查中，m -矮双星的距离分布比太阳型双星的分布更窄，在更小的距离处达到峰值。这通常被解释为意味着m矮星构成了从褐矮星到恒星的连续转变。本文采用动态居群综合（DPS）模型对m矮星分离分布进行了预测，其中具有迟型主星（≤1.5M⊙）的“星状”双星遵循通用初始分布函数，并在其出生嵌入星团中进行动态处理。一个独立的“类bd”星族有自己的双星分布函数和初始质量函数（IMF），其质量与恒星的IMF重叠。结合这两种形成模式，在晚期m矮星较宽的分离分布顶部有一个峰值，与晚期AstraLux样品一致。早期m矮星的DPS分离分布没有出现这样的峰值，这与m矮星的多倍分布（MinMS）数据一致。我们注意到，后一项调查可能与早期的AstraLux数据存在矛盾。总之，AstraLux和MinMS数据无法明确区分bd是否是恒星IMF的连续延伸。未来的观测工作需要充分回答这个有趣的问题。DPS模型预测，在AstraLux调查的灵敏度范围之外的双星仍有待探测。为了应用于未来的数据，我们提出了一种观测测量假定的类bd分支和恒星分支重叠的方法。我们讨论了普适恒星形成和分布函数的意义。
The separation distribution for M-dwarf binaries in the AstraLux survey is narrower and peaking at smaller separations than the distribution for solar-type binaries. This is often interpreted to mean that M-dwarfs constitute a continuous transition from brown dwarfs (BDs) to stars. Here a prediction for the M-dwarf separation distribution is presented, using a dynamical population synthesis (DPS) model in which “starlike” binaries with late-type primaries (≲ 1.5M⊙) follow universal initial distribution functions and are dynamically processed in their birth embedded clusters. A separate “BD-like” population has both its own distribution functions for binaries and initial mass function (IMF), which overlaps in mass with the IMF for stars. Combining these two formation modes results in a peak on top of a wider separation distribution for late M-dwarfs consistent with the late AstraLux sample. The DPS separation distribution for early M-dwarfs shows no such peak and is in agreement with the M-dwarfs in Multiples (MinMS) data. We note that the latter survey is potentially in tension with the early AstraLux data. Concluding, the AstraLux and MinMS data are unable to unambiguously distinguish whether or not BDs are a continuous extension of the stellar IMF. Future observational efforts are needed to fully answer this interesting question. The DPS model predicts that binaries outside the sensitivity range of the AstraLux survey remain to be detected. For application to future data, we present a means to observationally measure the overlap of the putative BD-like branch and the stellar branch. We discuss the meaning of universal star formation and distribution functions.