Substellar companions and isolated planetary-mass objects from protostellar disc fragmentation
Substellar companions and isolated planetary-mass objects from protostellar disc fragmentation
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DOI：
10.1111/j.1365-2966.2003.07317.x
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发表时间：
2003-10
影响因子：
4.8
通讯作者：
W. Rice;P. Armitage;I. Bonnell;M. Bate;S. Jeffers;S. Vine
中科院分区：
文献类型：
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作者：
W. Rice;P. Armitage;I. Bonnell;M. Bate;S. Jeffers;S. Vine
如果气体能在比轨道周期短的时间内冷却下来，自引力原恒星盘就不容易破碎。本文采用流体动力学模拟和n -体轨道积分相结合的方法，研究了一个初始质量比为M disc /M * = 0.1 i的破碎盘的长期演化过程。对于一个最初在半径范围内不稳定的盘，坍缩和随后的吸积的结合产生了质量光谱延伸（对于太阳质量的恒星，最高可达0.01 M O）的次恒星物体。随后的引力演化在几百万年内将大多数质量较低的天体抛射出去，只留下少数质量非常大的行星或棕矮星，它们在半径较小的偏心轨道上运行。基于这些结果，像HD 168443这样的星系——其中的伴星接近或超过了氘归向极限——似乎是通过引力不稳定性形成的最佳候选者。如果大质量的恒星伴星起源于盘裂，而低质量的行星伴星起源于核心吸积，那么半径为1 au的大质量恒星伴星的金属丰度分布应该与拥有低质量行星伴星的恒星不同。
Self-gravitating protostellar discs are unstable to fragmentation if the gas can cool on a time-scale that is short compared with the orbital period. We use a combination of hydrodynamic simulations and N-body orbit integrations to study the long-term evolution of a fragmenting disc with an initial mass ratio to the star of M d i s c /M * = 0.1 I . For a disc that is initially unstable across a range of radii, a combination of collapse and subsequent accretion yields substellar objects with a spectrum of masses extending (for a Solar-mass star up to 0.01 M O .. Subsequent gravitational evolution ejects most of the lower mass objects within a few million years, leaving a small number of very massive planets or brown dwarfs in eccentric orbits at moderately small radii. Based on these results, systems such as HD 168443 - in which the companions are close to or beyond the deuterium homing limit - appear to be the best candidates to have formed via gravitational instability. If massive substellar companions originate from disc fragmentation, while lower-mass planetary companions originate from core accretion, the metallicity distribution of stars which host massive substellar companions at radii of ∼1 au should differ from that of stars with lower mass planetary companions.