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arXiv 1408.6554astro-ph.EP
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吸积环行星星云：观测信号

Accreting Circumplanetary Disks: Observational Signatures

Zhaohuan Zhu

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10 pages, 3 figures, Accepted by ApJ
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摘要：

我用大气辐射传输模型计算了吸积环行星盘的光谱能量分布。只有在1米长的$_{J}$行星周围的$10^{-10} M_{\odot} yr^{-1}$处吸积的环行星盘才能比行星本身更亮。一个中等程度吸积的环行星盘（$\dot{M}\sim 10^{-8}M_{\odot} yr^{-1}$ ;足以在一百万年内形成一颗10 M $_{J}$行星）围绕着一颗1 M $_{J}$行星，其最高温度为$\sim$ 2000 K，在近红外波段（$J$、$H$、$K$波段），这个盘的亮度与一颗晚M型褐矮星或一颗“热启动”的10 M $_{J}$行星一样。使用直接成像来寻找低质量行星周围的吸积盘（例如，1 M $_{J}$），并将它们与褐矮星或热的大质量行星区分开来，在中红外波段（$L'$，$M$，$N$波段）获得测光是至关重要的，因为环行行星盘的辐射比褐矮星或行星的辐射向更长的波长衰减得更慢。如果年轻的行星有强磁场（$\gtrsim$ 100 G），磁场可能会截断缓慢吸积的环行星盘（$\dot{M}\lesssim10^{-9} M_{\odot} yr^{-1}$），并导致磁层吸积，这可以提供额外的吸积特征，如吸积激波和线发射的紫外/光学过量。

英文摘要：

I calculate the spectral energy distributions (SEDs) of accreting circumplanetary disks using atmospheric radiative transfer models. Circumplanetary disks only accreting at $10^{-10} M_{\odot} yr^{-1}$ around a 1 M$_{J}$ planet can be brighter than the planet itself. A moderately accreting circumplanetary disk ($\dot{M}\sim 10^{-8}M_{\odot} yr^{-1}$; enough to form a 10 M$_{J}$ planet within 1 Myr) around a 1 M$_{J}$ planet has a maximum temperature of $\sim$2000 K, and at near-infrared wavelengths ($J$, $H$, $K$ bands), this disk is as bright as a late M-type brown dwarf or a 10 M$_{J}$ planet with a "hot start". To use direct imaging to find the accretion disks around low mass planets (e.g., 1 M$_{J}$) and distinguish them from brown dwarfs or hot high mass planets, it is crucial to obtain photometry at mid-infrared bands ($L'$, $M$, $N$ bands) because the emission from circumplanetary disks falls off more slowly towards longer wavelengths than those of brown dwarfs or planets. If young planets have strong magnetic fields ($\gtrsim$100 G), fields may truncate slowly accreting circumplanetary disks ($\dot{M}\lesssim10^{-9} M_{\odot} yr^{-1}$) and lead to magnetospheric accretion, which can provide additional accretion signatures, such as UV/optical excess from the accretion shock and line emission.

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