We report the first detection of 3 μm water ice absorption in a protoplanetary disk. Low-resolution spectroscopy with Subaru IRCS was carried out for two T Tauri stars with an edge-on disk, HK Tau B and HV Tau C. A 3 μm deep water ice absorption (τ ≥ 1) toward both objects was detected. Contribution by foreground cloud material to the ice absorption should be small, since AV ≤ 3 toward HK Tau A and HV Tau A, HV Tau B. Although HV Tau C is reported to have a small amount of envelope material, its mass is insufficient to produce the large optical depth of the detected water ice. In addition, HK Tau B does not have any significant envelope mass. Therefore, the water ice exists inside the disks of these objects. The optical depth profile of the water ice absorption in the protoplanetary disks does not show any significant difference from those of protostellar sources. The water ice optical depth for HV Tau C showed a large variation (Δτ = 0.59) in two observing epochs separated by 2.32 yr. Assuming the ice absorption comes from a spherical cloud at 100 AU and Keplerian rotation, it suggests that a Pluto mass gas and dust cloud with a size of 1.4 AU may have passed by the line of sight. The lack of variability of the continuum level of HV Tau C at the two epochs implies that the dust grains with an icy mantle are segregated from the grains without an icy mantle.
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机译：我们报告了在原行星盘中首次检测到3μm水冰的吸收。用斯巴鲁IRCS进行的低分辨率光谱学是对两颗T型金牛座恒星，其边缘装有圆盘HK Tau B和HV TauC。检测到两个物体的3μm深水冰吸收（τ≥1）。前景云物质对冰吸收的贡献应该很小，因为朝向HK Tau A和HV Tau A，HV Tau B的AV≤3。尽管据报道HV Tau C的包膜材料较少，但其质量不足以产生检测到的水冰的大光学深度。另外，HK Tau B没有明显的包膜质量。因此，水冰存在于这些物体的圆盘内部。原行星盘中水冰吸收的光学深度分布与原恒星源的光学深度分布没有显着差异。 HV Tau C的水冰光学深度在相隔2.32年的两个观测纪元中显示出较大的变化（Δτ= 0.59）。假设冰的吸收来自100 AU的球形云和Keplerian旋转，这表明视线可能已经绕过了1.4 AU大小的冥王星气体和尘埃云。在两个时期，HV Tau C的连续水平没有变化，这意味着具有冰冷套层的尘埃颗粒与没有冰冷套层的尘埃颗粒分离。
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