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arXiv 1804.03075astro-ph.EP
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用分层贝叶斯模型研究热木星膨胀半径

Investigating hot-Jupiter inflated radii with hierarchical Bayesian modelling

Marko Sestovic, Brice-Olivier Demory, Didier Queloz

摘要:

到今天为止,已经发现了数百个热彗星,但其中很大一部分的膨胀半径仍然无法解释。目前还不清楚是否一个单一的暴胀机制足以解释整个半径分布,或者是否需要它们的组合。我们试图了解热木星半径与恒星辐射和质量的关系。我们的目标还在于发现由不可观测参数引起的半径上的内在物理散射。通过构建一个分层贝叶斯模型,我们推断了286颗气体巨星的行星半径,质量和入射通量之间的概率关系。我们分别纳入观测数据的不确定性和人口的内在物理分散。这使我们能够将半径中的固有物理散射(由于潜在参数,如重元素分数)作为待推断的参数。我们发现,行星的质量起着关键作用的膨胀程度,与行星在0.37 - 0.98 MJ之间的范围内显示最膨胀的半径。在更高的质量,半径响应入射通量开始减少。在0.37 +-0.03兆焦耳的阈值以下,我们发现巨系外行星作为一个群体无法保持大于1.4 RJ的膨胀半径,而是随着入射通量增加到超过10^6 Wm-2而表现出更小的尺寸。我们还发现,低于1兆焦耳,有一个截止点,在高入射通量超过我们发现没有更多的膨胀的行星,这个截止点随着质量的减少而减少。当入射通量大于1.6*10^6 Wm-2,质量范围为0.37 - 0.98 MJ时,我们没有发现非膨胀热彗星的证据。我们的研究证明了人口水平分析对掌握系外行星基本性质的重要性。

英文摘要:

As of today, hundreds of hot Jupiters have been found, yet the inflated radii of a large fraction of them remain unexplained. It is still unclear whether a single inflation mechanism is enough to explain the entire distribution of radii, or whether a combination of them is needed. We seek to understand the relationship of hot Jupiter radii with stellar irradiation and mass. We also aim to find the intrinsic physical scatter in their radii caused by unobservable parameters. By constructing a hierarchical Bayesian model, we infer the probabilistic relation between planet radius, mass and incident flux for a sample of 286 gas giants. We separately incorporate the observational uncertainties of the data and the intrinsic physical scatter in the population. This allows us to treat the intrinsic physical scatter in radii (due to latent parameters such as the heavy element fraction) as a parameter to be inferred. We find that the planetary mass plays a key role in the inflation extent, with planets in the range between 0.37 - 0.98 MJ showing the most inflated radii. At higher masses, the radius response to incident flux begins to decrease. Below a threshold of 0.37 +- 0.03 MJ we find that giant exoplanets as a population are unable to maintain inflated radii greater than 1.4 RJ but instead exhibit smaller sizes as the incident flux is increased beyond 10^6 Wm-2. We also find that below 1 MJ, there is a cutoff point at high incident flux beyond which we find no more inflated planets, and that this cutoff point decreases as the mass decreases. At incident fluxes higher than 1.6*10^6 Wm -2 and in a mass range 0.37 - 0.98 MJ, we find no evidence for a population of non-inflated hot Jupiters. Our study demonstrates the importance of population-level analysis to grasp the underlying properties of exoplanets.

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