HST ROTATIONAL SPECTRAL MAPPING OF TWO L-TYPE BROWN DWARFS: VARIABILITY IN AND OUT OF WATER BANDS INDICATES HIGH-ALTITUDE HAZE LAYERS
HST ROTATIONAL SPECTRAL MAPPING OF TWO L-TYPE BROWN DWARFS: VARIABILITY IN AND OUT OF WATER BANDS INDICATES HIGH-ALTITUDE HAZE LAYERS
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两个 L 型褐矮星的 HST 旋转光谱图：水带内外的变化表明高空雾霾层
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
A. Heinze
中科院分区：
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作者：
Hao Yang;D. Apai;M. Marley;D. Saumon;C. Morley;E. Buenzli;É. Artigau;Jacqueline Radigan;S. Metchev;A. Burgasser;S. Mohanty;P. Lowrance;A. Showman;T. Karalidi;D. Flateau;A. Heinze
我们展示了两颗L5矮星2 MASS J18212815+1414010和2 MASS J15074759 - 1627386的时间分辨近红外光谱，这些矮星是用哈勃太空望远镜（HST）上的广角相机3仪器观测到的。我们研究了1.1 μm ~ 1.7 μm的旋光调制通量随波长的变化。我们发现两个L5矮星在1.15 μm和1.4 μm处的水吸收带的变化幅度与相邻的连续谱相似。这与以前的L/T过渡矮星的HST观测结果不同，在1.4 μm处的水吸收显示出约为其他波长处振幅的一半的变化。我们发现从L5矮星到早期T矮星，水带外的通量变化相对于水带内的通量变化的相对幅度呈现出逐渐增大的趋势。我们利用Saumon和Marley的模型，发现所观察到的L5矮星的变化可以解释为存在的空间变化的高空霾层以上的冷凝云。因此，我们的观察表明，阴霾层的不均匀性的驱动程序的可变性必须位于非常低的压力，甚至水的不透明度是可以忽略不计的。在不久的将来，旋转光谱映射技术可以用于其他原子和分子物种，以探测棕矮星和系外行星大气中的不同压力水平，并揭示水平和垂直云结构。
We present time-resolved near-infrared spectroscopy of two L5 dwarfs, 2MASS J18212815+1414010 and 2MASS J15074759−1627386, observed with the Wide Field Camera 3 instrument on the Hubble Space Telescope (HST). We study the wavelength dependence of rotation-modulated flux variations between 1.1 μm and 1.7 μm. We find that the water absorption bands of the two L5 dwarfs at 1.15 μm and 1.4 μm vary at similar amplitudes as the adjacent continuum. This differs from the results of previous HST observations of L/T transition dwarfs, in which the water absorption at 1.4 μm displays variations of about half of the amplitude at other wavelengths. We find that the relative amplitude of flux variability out of the water band with respect to that in the water band shows a increasing trend from the L5 dwarfs toward the early T dwarfs. We utilize the models of Saumon & Marley and find that the observed variability of the L5 dwarfs can be explained by the presence of spatially varying high-altitude haze layers above the condensate clouds. Therefore, our observations show that the heterogeneity of haze layers—the driver of the variability—must be located at very low pressures, where even the water opacity is negligible. In the near future, the rotational spectral mapping technique could be utilized for other atomic and molecular species to probe different pressure levels in the atmospheres of brown dwarfs and exoplanets and uncover both horizontal and vertical cloud structures.