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BINARIES AND THE L DWARF/T DWARF TRANSITION

机译：双星与L DWARF / T DWARF过渡

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摘要

High-resolution imaging has revealed an unusually high binary fraction among objects spanning the transition between the L dwarf and T dwarf spectral classes. In an attempt to reproduce and unravel the origins of this apparent binary excess, I present a series of Monte Carlo mass function and multiplicity simulations of field brown dwarfs in the vicinity of the Sun. These simulations are based on solar metallicity brown dwarf evolutionary models and incorporate empirical luminosity and absolute magnitude scales, measured multiplicity statistics, and observed spectral templates in the construction and classification of composite binary spectra. In addition to providing predictions for the number and surface density distributions of L and T dwarfs for volume-limited and magnitude-limited samples, these simulations successfully reproduce the observed binary fraction distribution assuming an intrinsic (resolved) binary fraction of 11_(-3)~(+6)% (95% confidence interval), consistent with prior determinations. However, the true binary fraction may be as high as 40% if, as suggested by Liu et al., a significant fraction of L/T transition objects (～66%) are tightly bound, unresolved multiples. The simulations presented here demonstrate that the binary excess among L/T transition objects arises primarily from the flattening of the luminosity scale over these spectral types and is not inherently the result of selection effects incurred in current magnitude-limited imaging samples. Indeed, the existence of a binary excess can be seen as further evidence that brown dwarfs traverse the L/T transition rapidly, possibly driven by a nonequilibrium submergence of photospheric condensates.
机译：高分辨率成像揭示了跨越L矮星和T矮星光谱类别之间过渡的物体中异常高的二进制分数。为了重现和阐明这种明显的二元过量的起源，我提出了一系列蒙特卡洛质量函数和太阳附近野棕矮星的多重模拟。这些模拟基于太阳金属性褐矮星演化模型，并在组合二元光谱的构建和分类中结合了经验光度和绝对量级标度，测得的多重统计量以及观察到的光谱模板。除了为体积受限和幅度受限的样本提供L和T小矮人的数量和表面密度分布的预测外，这些模拟还假设固有（解析）二进制分数为11 _（-3），成功地再现了观察到的二进制分数分布。 〜（+6）％（95％置信区间），与先前的确定一致。但是，如Liu等人的建议，如果L / T过渡物体的很大一部分（〜66％）紧密结合且未解决，则真实的二元分数可能高达40％。此处提供的模拟结果表明，L / T过渡对象之间的二进制过量主要是由于这些光谱类型上的光度标度趋于平坦而引起的，而不是固有地不是当前幅度受限的成像样本中产生选择效应的结果。确实，二元过量的存在可以看作是进一步的证据，表明褐矮星可能很快通过L / T跃迁，这可能是由光球凝结液的非平衡淹没驱动的。

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