arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2001.06558astro-ph.EPastro-ph.SR
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辐照褐矮星WD0137-349B的简化三维GCM模拟

Simplified 3D GCM modelling of the irradiated brown dwarf WD0137-349B

Elspeth K. H. Lee, Sarah L. Casewell, Katy L. Chubb, Mark Hammond, Xianyu Tan, Shang-Min Tsai, Raymond T. Pierrehumbert

摘要:

内容:白矮星-棕矮星短周期双星(P $_{\rm orb}$ $\lesssim$ 2小时)是一些已知的最极端的辐射大气环境。这些系统提供了一个机会,探索不同的典型热木星系统的辐照大气的理论和建模工作。目的:研究棕矮星WD 0137 - 349 B的三维大气结构和动力学性质。方法:采用三维GCM模式Exo-FMS,采用双波段灰色辐射传输方案,模拟WD 0137 - 349 B的大气。用三维蒙特卡罗辐射传输模式\textsc{cmcrt}对GCM模式的结果进行后处理。结果:我们的研究结果表明,WD 0137 - 349 B的昼夜能量输送效率低下,昼夜温度差异大。存在多种流型,根据其纬向和纬度向东或向西不对称地转移能量。翻转区域产生于西终结者。我们能够重现的开始系统近红外发射过量$\gtrsim$ 1.95 $μ$ m的GNIRS仪器所观察到的。我们的模型通过$\approx$ 1-3的因子过度预测了IR相曲线通量,但通常很好地拟合了相曲线的形状。使用\textsc{vulcan}的化学动力学模型表明,在高海拔地区,一个高度电离的区域可以形成在棕矮星的向阳面。结论:我们首次尝试在三维环境中模拟短周期白矮星-棕矮星双星的大气。需要进一步研究紫外线照射的辐射和光化学加热,以更准确地捕获棕矮星大气层内的能量平衡。云的形成也可能在形成褐矮星的发射光谱中起重要作用。

英文摘要:

Context: White dwarf - Brown dwarf short period binaries (P$_{\rm orb}$ $\lesssim$ 2 hours) are some of the most extreme irradiated atmospheric environments known. These systems offer an opportunity to explore theoretical and modelling efforts of irradiated atmospheres different to typical hot Jupiter systems. Aims: We aim to investigate the three dimensional atmospheric structural and dynamical properties of the Brown dwarf WD0137-349B. Methods: We use the three dimensional GCM model Exo-FMS, with a dual-band grey radiative-transfer scheme to model the atmosphere of WD0137-349B. The results of the GCM model are post-processed using the three dimensional Monte Carlo radiative-transfer model \textsc{cmcrt}. Results: Our results suggest inefficient day-night energy transport and a large day-night temperature contrast for WD0137-349B. Multiple flow patterns are present, shifting energy asymmetrically eastward or westward depending on their zonal direction and latitude. Regions of overturning are produced on the western terminator. We are able to reproduce the start of the system near-IR emission excess at $\gtrsim$ 1.95 $μ$m as observed by the GNIRS instrument. Our model over predicts the IR phase curve fluxes by factors of $\approx$1-3, but generally fits the shape of the phase curves well. Chemical kinetic modelling using \textsc{vulcan} suggests a highly ionised region at high altitudes can form on the dayside of the Brown dwarf. Conclusions: We present a first attempt at simulating the atmosphere of a short period White dwarf - Brown dwarf binary in a 3D setting. Further studies into the radiative and photochemical heating from the UV irradiation is required to more accurately capture the energy balance inside the Brown dwarf atmosphere. Cloud formation may also play an important role in shaping the emission spectra of the Brown dwarf.

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