Predicting the properties of binary stellar systems: the evolution of accreting protobinary systems
Predicting the properties of binary stellar systems: the evolution of accreting protobinary systems
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DOI：
10.1046/j.1365-8711.2000.03333.x
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发表时间：
2000-02
影响因子：
4.8
通讯作者：
M. Bate
中科院分区：
文献类型：
--
作者：
M. Bate
我们研究双星系统的形成。我们考虑一个模型，其中的“种子”原双星系统的形式，通过分裂，在一个崩溃的分子云核心和发展到其最终质量的吸积材料从下落的气体信封。这种吸积改变了双星的质量比和轨道，并且是形成拱星盘和/或拱双星盘的主要原因。鉴于这个模型的二元形成，我们预测的二元系统的性质，以及它们如何依赖于分子云核心内的初始条件。我们预测，应该有一个连续的趋势，这样更接近的双星更有可能有质量相等的组件，更有可能有circumbinary光盘比更广泛的系统。比较我们的结果与观测，我们发现，观测到的双星质量比分布和作为分离函数的环双星盘的频率最容易再现，如果祖分子云核的径向密度分布在均匀和1/r之间（例如，高斯），具有近似均匀的旋转。这与观测到的星前核的性质非常一致。相反，我们发现，所观察到的性质的双星不能被复制，如果云核是在固体旋转，并具有初始密度分布是强烈的中心凝聚。最后，与太阳系外行星的径向速度搜索相一致，我们发现，很难形成一个棕矮星伴星的太阳型星星与一个巨大的分离10 Au，但棕矮星伴星的频率应该增加较大的分离或较低的质量的主。
We investigate the formation of binary stellar systems. We consider a model where a ‘seed’ protobinary system forms, via fragmentation, within a collapsing molecular cloud core and evolves to its final mass by accreting material from an infalling gaseous envelope. This accretion alters the mass ratio and orbit of the binary, and is largely responsible for forming the circumstellar and/or circumbinary discs. Given this model for binary formation, we predict the properties of binary systems and how they depend on the initial conditions within the molecular cloud core. We predict that there should be a continuous trend such that closer binaries are more likely to have equal-mass components and are more likely to have circumbinary discs than wider systems. Comparing our results with observations, we find that the observed mass-ratio distributions of binaries and the frequency of circumbinary discs as a function of separation are most easily reproduced if the progenitor molecular cloud cores have radial density profiles between uniform and 1/r (e.g., Gaussian) with near-uniform rotation. This is in good agreement with the observed properties of pre-stellar cores. Conversely, we find that the observed properties of binaries cannot be reproduced if the cloud cores are in solid-body rotation and have initial density profiles which are strongly centrally condensed. Finally, in agreement with the radial-velocity searches for extrasolar planets, we find that it is very difficult to form a brown dwarf companion to a solar-type star with a separation ≲10 au, but that the frequency of brown dwarf companions should increase with larger separations or lower mass primaries.