原恒星盘形成机制:角动量守恒与磁制动

Hsi-Wei Yen and Yueh-Ning Lee
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引用次数: 0

摘要

年轻原恒星周围的原恒星盘表现出多种多样的特性,其半径从不到十个天文单位到几百个天文单位不等。为了研究形成这种星盘半径分布的机制,我们从文献中收集了27颗0级和I级单颗原恒星的样本,这些原恒星的星盘已经解析,原恒星质量也已经动态测定。此外,我们还根据文献中观测到的比角动量剖面,推导出了致密内核中旋转与重力能量比的径向剖面。利用这些观测到的原恒星质量和旋转能量曲线,我们通过 Y.-N. Lee et al.Lee et al.中的流体力学和非理想磁流体动力学(MHD)模型计算出理论圆盘半径,并生成合成样本与观测数据进行比较。在我们的理论模型中,当中心原恒星+磁盘质量较低时,磁盘半径由流体力学决定。原恒星和磁盘长大并超过一定质量后,磁盘半径会受到磁制动和非理想 MHD 效应的调节。该模型合成的星盘半径分布与观测结果非常吻合。这一结果表明,流体力学和非理想 MHD 可以在不同质量区(或演化阶段)起主导作用,这取决于旋转能量和原恒星+磁盘质量。这个模型很自然地解释了大(>100 au)盘的罕见性和非常小(<10 au)盘的存在。它还预言,大多数原恒星盘的半径为几十个天文单位,正如观测到的那样。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Protostellar Disk Formation Regimes: Angular Momentum Conservation versus Magnetic Braking
Protostellar disks around young protostars exhibit diverse properties, with their radii ranging from less than ten to several hundred astronomical units. To investigate the mechanisms shaping this disk radius distribution, we compiled a sample of 27 Class 0 and I single protostars with resolved disks and dynamically determined protostellar masses from the literature. Additionally, we derived the radial profile of the rotational-to-gravitational-energy ratio in dense cores from the observed specific angular momentum profiles in the literature. Using these observed protostellar masses and rotational energy profile, we computed theoretical disk radii from the hydrodynamic and nonideal magnetohydrodynamic (MHD) models in Y.-N. Lee et al. and generated synthetic samples to compare with the observations. In our theoretical model, the disk radii are determined by hydrodynamics when the central protostar+disk mass is low. After the protostars and disks grow and exceed certain masses, the disk radii become regulated by magnetic braking and nonideal MHD effects. The synthetic disk radius distribution from this model matches well with the observations. This result suggests that hydrodynamics and nonideal MHD can be dominant in different mass regimes (or evolutionary stages), depending on the rotational energy and protostar+disk mass. This model naturally explains the rarity of large (>100 au) disks and the presence of very small (<10 au) disks. It also predicts that the majority of protostellar disks have radii of a few tens of astronomical units, as observed.
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