论金属丰度与巨行星存在的相关性
On the correlation between metallicity and the presence of giant planets
摘要：
恒星金属丰度和巨行星存在之间的相关性已经得到了很好的证实。这一现象被初步解释为金属含量增加的恒星盘中可能增加了行星形成的几率。然而，这一解释有两点需要注意。首先，有行星的巨星并不像矮星那样，呈现出金属丰度分布偏向富含金属的天体。第二，与金属丰度的相关性在中等金属丰度下是无效的，因为在中等金属丰度下，可以发现巨行星优先绕厚盘恒星运行。这两个特点都不能用巨型行星形成的假设来解释。我们认为它们本质上是银河系的，可能与巨行星的形成过程无关。这表明，相同的动力学效应，即恒星在银盘中的迁移，是这两种特征的起源，重要的后果是，大多数富含金属的恒星承载巨行星起源于内盘，这一性质迄今为止在很大程度上被忽视。我们说明，一个行星的金属丰度的相关性类似于所观察到的是很容易得到的，如果从内部磁盘的恒星有一个更高的比例比恒星出生在太阳半径的巨行星，没有具体的依赖金属丰度。我们认为，内星系盘（分子环）中的分子氢密度可能在设定来自该地区的高比例巨行星中发挥作用。
英文摘要：
The correlation between stellar metallicity and the presence of giant planets is well established. It has been tentatively explained by the possible increase of planet formation probability in stellar disks with enhanced amount of metals. However, there are two caveats to this explanation. First, giant stars with planets do not show a metallicity distribution skewed towards metal-rich objects, as found for dwarfs. Second, the correlation with metallicity is not valid at intermediate metallicities, for which it can be shown that giant planets are preferentially found orbiting thick disk stars. None of these two peculiarities is explained by the proposed scenarios of giant planet formation. We contend that they are galactic in nature, and probably not linked to the formation process of giant planets. It is suggested that the same dynamical effect, namely the migration of stars in the galactic disk, is at the origin of both features, with the important consequence that most metal-rich stars hosting giant planets originate from the inner disk, a property that has been largely neglected until now. We illustrate that a planet-metallicity correlation similar to the observed one is easily obtained if stars from the inner disk have a higher percentage of giant planets than stars born at the solar radius, with no specific dependence on metallicity. We propose that the density of molecular hydrogen in the inner galactic disk (the molecular ring) could play a role in setting the high percentage of giant planets that originate from this region.
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