Atmospheres of protoplanetary cores: Critical mass for nucleated instability
Atmospheres of protoplanetary cores: Critical mass for nucleated instability
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DOI：
10.1086/505695
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发表时间：
2006-09-01
影响因子：
4.9
通讯作者：
Rafikov, Roman R.
中科院分区：
文献类型：
--
作者：
Rafikov, Roman R.
本文系统地研究了吸积原行星核的准静态大气层的不同不透明度行为和原行星星云不同部分的实际星子吸积率。我们证明了有两类重要的大气：（1）具有与周围星云气体平滑融合的外部对流区的大气，以及（2）具有几乎等温的外部辐射区的大气，有效地将大气内部从星云中分离出来。在一个给定的核心周围积聚的大气类型取决于核心质量、星云参数和核心的吸积光度。在原行星盘内部的核心（距离太阳大约0.3 Au）有很大的光度，导致第一种类型的大气，而在巨行星区域的核心（超过几个Au）有很小的吸积光度，总是积累大量的第二种类型的大气。核不稳定性开始所需的临界核心质量被发现有很大的变化，作为一个函数，从太阳的距离。这个质量在0.1-1 Au处为5-20 M圆，这太大而不允许通过在原位生长的核心周围的成核不稳定性形成“热超导体”。在巨行星区域，临界核心质量取决于气体不透明度和星子吸积率，但对星云温度或密度不敏感，前提是外部辐射区域的不透明度不取决于气体密度（例如，灰尘不透明度）。如果小行星的吸积速度足够快，在星云气体消散之前形成原行星核，那么巨行星区域的临界质量可以高达20-60 M圈（不透明度为0.1 cm（2）g（-1））。
We systematically study quasi- static atmospheres of accreting protoplanetary cores for different opacity behaviors and realistic planetesimal accretion rates in various parts of the protoplanetary nebula. We demonstrate that there are two important classes of atmospheres: ( 1) those having an outer convective zone that smoothly merges with the surrounding nebular gas, and ( 2) those possessing an almost isothermal outer radiative region that effectively decouples the atmospheric interior from the nebula. The type of atmosphere accumulating around a given core depends on the core mass, nebular parameters, and accretion luminosity of the core. Cores in the inner parts of the protoplanetary disk ( within roughly 0.3 AU from the Sun) have large luminosities resulting in atmospheres of the first type, while cores in the giant planet region ( beyond several AU) have small accretion luminosities and always accumulate massive atmospheres of the second type. The critical core mass needed for the nucleated instability to commence is found to vary considerably as a function of distance from the Sun. This mass is 5-20 M circle plus at 0.1-1 AU, which is too large to permit the formation of ''hot Jupiters'' by nucleated instability around the cores that have grown in situ. In the region of giant planets the critical core mass depends on the gas opacity and planetesimal accretion rate but is insensitive to the nebular temperature or density provided that the opacity in the outer radiative region does not depend on the gas density ( e.g., dust opacity). The critical mass in the region of giant planets can be as high as 20-60 M circle plus ( for an opacity of 0.1 cm(2) g(-1)) if planetesimal accretion is fast enough for protoplanetary cores to form prior to the nebular gas dissipation.