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arXiv 1808.03293astro-ph.EP
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行星形成:一种优化的种群合成方法

Planet Formation: An Optimized Population-Synthesis Approach

John Chambers

摘要:

利用粒子数综合方法研究了行星形成的物理过程。我们发展了一个简单的行星生长模型,包括卵石和气体吸积,以及在一个不断发展的原行星盘中的轨道迁移。该模型是运行人口的2000个恒星的磁盘质量和半径的范围内,和初始原行星轨道。所得到的行星分布与观测到的太阳系外行星的人口进行比较,并使用粒子群优化方案迭代地改进模型参数。最终的行星系的特征主要由卵石隔离质量控制,这是一颗行星的质量,它足以扰动附近的气体,使漂移的卵石停止向内流动,停止生长。卵石隔离质量随着轨道距离的增加而增加,因此巨大的行星核心只能在外盘中形成。巨人向内迁移,在最后的轨道距离范围内居住。最适合的模型具有大的初始原行星质量,短的卵石漂移时间尺度,低磁盘粘度和短的大气冷却时间,所有这些都促进了快速增长。该模型成功地再现了观测到的巨行星和棕矮星的频率和分布。对于单行星系统来说,超级地球的适合性较差,但当包含更多的原行星时,它会稳步提高。虽然这项研究的目的是为了匹配太阳系外行星的分布,但类似于太阳系的系统中有1-2%至少包含4颗原行星。

英文摘要:

The physics of planet formation is investigated using a population synthesis approach. We develop a simple model for planetary growth including pebble and gas accretion, and orbital migration in an evolving protoplanetary disk. The model is run for a population of 2000 stars with a range of disk masses and radii, and initial protoplanet orbits. The resulting planetary distribution is compared with the observed population of extrasolar planets, and the model parameters are improved iteratively using a particle swarm optimization scheme. The characteristics of the final planetary systems are mainly controlled by the pebble isolation mass, which is the mass of a planet that perturbs nearby gas enough to halt the inward flux of drifting pebbles and stop growth. The pebble isolation mass increases with orbital distance so that giant planet cores can only form in the outer disk. Giants migrate inwards, populating a wide range of final orbital distances. The best model fits have large initial protoplanet masses, short pebble drift timescales, low disk viscosities, and short atmospheric cooling times, all of which promote rapid growth. The model successfully reproduces the observed frequency and distribution of giant planets and brown dwarfs. The fit for super Earths is poorer for single-planet systems, but improves steadily when more protoplanets are included. Although the study was designed to match the extrasolar planet distribution, analogs of the Solar System form in 1-2% of systems that contain at least 4 protoplanets.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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