褐矮星大气中的纬度化学和云变化
Latitudinal chemical and cloud variations in the atmosphere of a brown dwarf
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中文总结 AI 辅助
研究褐矮星大气，提出差分分子旋转展宽新方法，通过对褐矮星DENIS J0255 - 4700观测，证实其大气存在纬度化学变化，数据显示低纬度CH4和NH3消耗，该方法可用于多颗褐矮星和系外行星大气研究。
中文摘要 AI 辅助
褐矮星是太阳系外巨行星的巨大类似物。与通常受明亮主星存在限制观测的系外行星相比，褐矮星是研究次恒星大气物理、化学和动力学的理想目标。先前对其大气的观测和模拟表明，赤道附近优先形成云，并伴有赤道 - 极地热梯度。本文表明这种大气结构应会导致通过多普勒效应可检测到的纬度化学变化。我们引入了一种新方法——差分分子旋转展宽，即比较高分辨率光谱中单个分子的表观旋转展宽。将此方法应用于褐矮星DENIS J0255 - 4700大气中不同分子（CO、H2O、CH4和NH3）的VLT - CRIRES观测，证实了纬度化学变化的存在。我们的数据表明低纬度地区CH4和NH3的消耗，与赤道云带一致。我们的方法可应用于多个褐矮星和系外行星以绘制其大气并研究各种大气过程。
英文摘要
Brown dwarfs are massive analogues of extrasolar giant planets. Compared to exoplanets whose observations are generally limited by the presence of their bright host star, brown dwarfs are ideal targets for studying substellar atmospheric physics, chemistry and dynamics. Previous observations and simulations of their atmospheres suggest preferential cloud formation around the equator, associated with an equator-pole thermal gradient. Here we show that this atmospheric structure should induce latitudinal chemical variations detectable by the Doppler effect. We introduce a new method - Differential Molecular Rotational Broadening - which consists in comparing the apparent rotational broadening of individual molecules from high-resolution spectra. Application of this approach to VLT-CRIRES observations for different molecules (CO, H2O, CH4 and NH3) in the atmosphere of the brown dwarf DENIS J0255-4700 confirms the existence of latitudinal chemical variations. Our data suggest a depletion of CH4 and NH3 at low latitudes, consistent with an equatorial cloud belt. Our method could be applied to multiple brown dwarfs and exoplanets to map their atmospheres and to study various atmospheric processes.
