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Near-Infrared Observations of Neptune’s Tropospheric Cloud Layer with the Lick Observatory Adaptive Optics System

机译:利克天文台自适应光学系统对海王星对流层云层的近红外观测

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We provide one of the first constraints on the combined infrared single-scattering albedo and opacity of Neptune's upper tropospheric cloud layer. For the observations, we used the adaptive optics system on the Lick Observatory's 3 m Shane Telescope (Mount Hamilton, California). The cloud layer is thought to be composed of H2S and extend up to 3.5–4.5 bars. Previously, the single-scattering albedo was measured in the range 0.2–0.94 μm and found to be extremely high (>0.8), but decreasing with increasing wavelength. Assuming an optically thick cloud, we find the best-fit single-scattering albedo of a 3.5 bar layer to be 0.23 at 1.27 μm and 0.18 at 1.56 μm. Uncertainties in the column density of haze above the cloud layer, and from deconvolution to remove contaminating light scattered by the point-spread function from infrared-bright features, indicate that the cloud could be even darker, but it is unlikely to be brighter than we report. The cloud particles could be brighter than we report if the total near-infrared opacity of the cloud is very low or the cloud's scattering phase function is significantly more forward-scattering at 1.2–1.6 μm than at 0.75 μm.
机译:我们提供了结合红外单散射反照率和海王星对流层上层云层不透明度的首个约束条件之一。对于观测,我们在利克天文台的3 m Shane望远镜(加利福尼亚州汉密尔顿)上使用了自适应光学系统。云层被认为是由H2S组成,延伸到3.5–4.5 bar。以前,单散射反照率的测量范围为0.2–0.94μm,发现极高(> 0.8),但随着波长的增加而降低。假设云层光学较厚,我们发现3.5 bar层的最佳拟合单散射反照率在1.27μm时为0.23,在1.56μm时为0.18。云层上方的雾度的柱密度不确定,以及通过反卷积以消除由红外明亮特征的点扩散函数散射的污染光的不确定性,表明云可能更暗,但不太可能比我们更亮报告。如果云的总近红外不透明度非常低,或者云的散射相位函数在1.2–1.6μm处比在0.75μm处的正向散射要大得多,则云粒子可能比我们报告的更亮。

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