极涡假说:不断演变、光谱截然不同的极区解释了褐矮星和巨型系外行星的短期和长期光曲线演变以及色倾角趋势

Nguyen Fuda and Dániel Apai
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引用次数: 0

摘要

最近的研究揭示了褐矮星与视角有关的颜色和光谱趋势,以及长期的光度变化(∼100 小时)。这些趋势的起源尚未得到解释。在这里,我们提出这些看似互不相关的观测结果都源于同一个现象:褐矮星和直接成像系外行星的极区在光谱上不同于低纬度区域,而且它们的演化时间尺度更长,可能是由极地漩涡驱动的。我们通过一个能够模拟超冷大气时间序列和磁盘积分光谱的时空大气模型来探索这一假设。我们研究了三种具有不同光谱和时间成分的情景:一种是没有极地涡旋的空假设,另一种是有极地涡旋的情景。我们发现,有极地漩涡的情景可以解释观测到的红外颜色倾角趋势和变率振幅倾角趋势。褐矮星和巨型系外行星大气中存在光谱上不同的、随时间演变的极区,这就提出了一种可能性,即一维静态大气模型可能不足以详细再现超冷大气。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
The Polar Vortex Hypothesis: Evolving, Spectrally Distinct Polar Regions Explain Short- and Long-term Light-curve Evolution and Color–Inclination Trends in Brown Dwarfs and Giant Exoplanets
Recent studies revealed viewing-angle-dependent color and spectral trends in brown dwarfs, as well as long-term photometric variability (∼100 hr). The origins of these trends are yet unexplained. Here, we propose that these seemingly unrelated sets of observations stem from the same phenomenon: the polar regions of brown dwarfs and directly imaged exoplanets are spectrally different from lower-latitude regions, and they evolve over longer timescales, possibly driven by polar vortices. We explore this hypothesis via a spatiotemporal atmosphere model capable of simulating time series and disk-integrated spectra of ultracool atmospheres. We study three scenarios with different spectral and temporal components: a null hypothesis without polar vortex, and two scenarios with polar vortices. We find that the scenarios with polar vortex can explain the observed infrared color–inclination trend and the variability amplitude–inclination trend. The presence of spectrally distinct, time-evolving polar regions in brown dwarfs and giant exoplanet atmospheres raises the possibility that one-dimensional static atmospheric models may be insufficient for reproducing ultracool atmospheres in detail.
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