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arXiv 1609.03019astro-ph.EP
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系外行星形成历史对热彗星可观测的现今光谱的影响

The imprint of exoplanet formation history on observable present-day spectra of hot Jupiters

Christoph Mordasini, Roy van Boekel, Paul Mollière, Thomas Henning, Björn Benneke

摘要:

行星大气层的组成是由它的形成、演化和现今的日照决定的。因此,行星的光谱可能包含其起源的线索。我们提出了一个“链”的模型,连接到其可观察到的当今光谱的行星的形成。链环节包括(1)行星的形成和迁移,(2)它的长期热力学演化,(3)各种磁盘化学模型,(4)非灰色大气模型,(5)辐射模型,以获得模拟光谱观测与JWST和ARIEL。在我们的标准化学模型中,内盘中的难熔碳是耗尽的,就像太阳系和被太阳系外星子污染的白矮星一样。我们的主要发现是:(1)在形成过程中由微行星撞击产生的包层浓缩决定了热彗星的最终行星大气成分。根据这一发现,我们研究了两种原型形成途径:水冰线内部或外部的形成,分别称为“干”和“湿”行星。(2)“干”和“湿”行星都是富氧的(C/O<1),这是由于固体建筑块的富氧性质。对于标准的碳消耗,“干”行星的C/O比<0.2,而“湿”行星的典型C/O值在0.1和0.5之间,主要取决于笼形物形成效率。只有非标准的磁盘化学没有碳消耗导致富碳的C/O比>1的“干燥”的星球。(3)虽然我们一直发现C/O比<1,但它们仍然有很大的差异。为了将形成历史与特定的C/O联系起来,因此需要更好地理解磁盘化学。

英文摘要:

The composition of a planet's atmosphere is determined by its formation, evolution, and present-day insolation. A planet's spectrum therefore may hold clues on its origins. We present a "chain" of models, linking the formation of a planet to its observable present-day spectrum. The chain links include (1) the planet's formation and migration, (2) its long-term thermodynamic evolution, (3) a variety of disk chemistry models, (4) a non-gray atmospheric model, and (5) a radiometric model to obtain simulated spectroscopic observations with JWST and ARIEL. In our standard chemistry model the inner disk is depleted in refractory carbon as in the Solar System and in white dwarfs polluted by extrasolar planetesimals. Our main findings are: (1) Envelope enrichment by planetesimal impacts during formation dominates the final planetary atmospheric composition of hot Jupiters. We investigate two, under this finding, prototypical formation pathways: a formation inside or outside the water iceline, called "dry" and "wet" planets, respectively. (2) Both the "dry" and "wet" planets are oxygen-rich (C/O<1) due to the oxygen-rich nature of the solid building blocks. The "dry" planet's C/O ratio is <0.2 for standard carbon depletion, while the "wet" planet has typical C/O values between 0.1 and 0.5 depending mainly on the clathrate formation efficiency. Only non-standard disk chemistries without carbon depletion lead to carbon-rich C/O ratios >1 for the "dry" planet. (3) While we consistently find C/O ratios <1, they still vary significantly. To link a formation history to a specific C/O, a better understanding of the disk chemistry is thus needed.

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