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arXiv 1102.5089astro-ph.EPastro-ph.SR
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具有厚云的大质量气体巨星的模型大气:应用于HR 8799行星和对未来探测的预测

Model atmospheres for massive gas giants with thick clouds: Application to the HR 8799 planets and predictions for future detections

Nikku Madhusudhan, Adam Burrows, Thayne Currie

摘要:

我们已经生成了一套广泛的新的大质量巨行星大气模型,并使用它来获得行星HR 8799 b、c和d的光度数据的拟合。我们考虑了广泛的多云和无云模型。云模型结合了不同的几何和光学厚度,模态颗粒尺寸和金属丰度。对于每一颗行星和一组云参数,我们探索重力和有效温度的网格,从而确定对行星质量和年龄的限制。我们的新模型对数据产生了统计上显著的拟合,并最终证实HR 8799行星的云比解释典型L和T矮星数据所需的云厚得多。两种模型都符合数据,1)物理厚的镁橄榄石云和60微米的模态颗粒尺寸和2)云由1微米大小的纯铁液滴和1%的过饱和度。目前的数据不足以精确地限制云的微观特性,如成分和颗粒大小。HR 8799 b、HR 8799 c和HR 8799 d的最佳估计质量范围分别为2-12 M_J、6-13 M_J和3-11 M_J,这意味着它们的年龄在1000万年到1.5亿万年之间,与先前报道的恒星年龄一致。最佳拟合的温度和重力略低于Currie等人(2011年)使用更厚的云模型获得的值。最后,我们使用这些模型来预测即将成像的行星的近中红外颜色。我们的模型预测,行星质量的对象遵循的轨迹在一些近中红外色星等图,是明确地从标准的L/T矮轨迹场棕矮星分离。

英文摘要:

We have generated an extensive new suite of massive giant planet atmosphere models and used it to obtain fits to photometric data for the planets HR 8799b, c, and d. We consider a wide range of cloudy and cloud-free models. The cloudy models incorporate different geometrical and optical thicknesses, modal particle sizes, and metallicities. For each planet and set of cloud parameters, we explore grids in gravity and effective temperature, with which we determine constraints on the planet's mass and age. Our new models yield statistically significant fits to the data, and conclusively confirm that the HR 8799 planets have much thicker clouds than those required to explain data for typical L and T dwarfs. Both models with 1) physically thick forsterite clouds and a 60-micron modal particle size and 2) clouds made of 1 micron-sized pure iron droplets and 1% supersaturation fit the data. Current data are insufficient to accurately constrain the microscopic cloud properties, such as composition and particle size. The range of best-estimated masses for HR 8799b, HR 8799c, and HR 8799d conservatively span 2-12 M_J, 6-13 M_J, and 3-11 M_J, respectively and imply coeval ages between ~10 and ~150 Myr, consistent with previously reported stellar age. The best-fit temperatures and gravities are slightly lower than values obtained by Currie et al. (2011) using even thicker cloud models. Finally, we use these models to predict the near-to-mid IR colors of soon-to-be imaged planets. Our models predict that planet-mass objects follow a locus in some near-to-mid IR color-magnitude diagrams that is clearly separable from the standard L/T dwarf locus for field brown dwarfs.

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