Nature2014-06-26 4:32 PM

一个附近褐矮星上的天气变化 A global cloud map of the nearest known brown dwarf

论文摘要 

最近发现的被称为Luhman 16AB的系统是由两个褐矮星(比行星大得多、但又没有大到足以成为恒星的天体)组成的一个双星体系,距我们仅仅六光年。只有“半人马座阿尔法星”和“巴纳德星”比它更近。现在,Ian Crossfield等人在近红外波段测绘了褐矮星Luhman 16B的表面,发现了表示存在云块的大尺度表面模式。监测表明,该天体全球气候模式演变的特征时间尺度大约为一天。对褐矮星上天气模式演变做进一步观测,有可能为了解全球循环条件怎样影响褐矮星和巨大太阳系外行星上的尘埃大气提供一个新基准。

Abstract 

Brown dwarfs—substellar bodies more massive than planets but not massive enough to initiate the sustained hydrogen fusion that powers self-luminous stars—are born hot and slowly cool as they age. As they cool below about 2,300 kelvin, liquid or crystalline particles composed of calcium aluminates, silicates and iron condense into atmospheric ‘dust’, which disappears at still cooler temperatures (around 1,300 kelvin). Models to explain this dust dispersal include both an abrupt sinking of the entire cloud deck into the deep, unobservable atmosphere and breakup of the cloud into scattered patches (as seen on Jupiter and Saturn9). However, hitherto observations of brown dwarfs have been limited to globally integrated measurements, which can reveal surface inhomogeneities but cannot unambiguously resolve surface features. Here we report a two-dimensional map of a brown dwarf’s surface that allows identification of large-scale bright and dark features, indicative of patchy clouds. Monitoring suggests that the characteristic timescale for the evolution of global weather patterns is approximately one day.

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