在M43区域的剪影盘中发现结晶水冰
Discovery of Crystallized Water Ice in a Silhouette Disk in the M43 Region
摘要：
本文给出了M42和M43区5颗亮（L<11.2）年轻恒星的1.9- 4.2 μ m光谱，它们与39- 80度的中到大倾角的剪影盘有关。在d121-1925和d216-0939附近观察到水冰吸收，而d182-316、d183-405和d218-354的光谱在检测限内的3.1 μ m附近没有显示水冰特征。通过比较邻近恒星的水冰特征，我们发现d121-1925和d216-0939的水冰吸收最有可能分别来自前景物质和周围的盘。发现盘的倾角是造成五颗年轻恒星水冰光学厚度差异的主要原因。我们的结果表明，有一个临界倾角为65度和75度之间的拱盘水冰的吸收变得强烈。发现d216-0939的圆盘表面的平均密度为6.38x10^（-18）g cm^（-3）。d216-0939盘中的水冰吸收带是显著的，因为水冰带的最大光学深度在比以前检测到的更长的波长处。这表明，该特征的主要载体是d216-0939圆盘表面的纯结晶水冰，其特征尺寸为~ 0.8 μ m，这表明晶粒生长。这是第一次直接探测到剪影盘中的纯结晶水冰。
英文摘要：
We present the 1.9--4.2um spectra of the five bright (L<11.2) young stars associated with silhouette disks with moderate to high inclination angle of 39--80deg in the M42 and M43 regions. The water ice absorption is seen toward d121-1925 and d216-0939, while the spectra of d182-316, d183-405, and d218-354 show no water ice feature around 3.1um within the detection limits. By comparing the water ice features toward nearby stars, we find that the water ice absorption toward d121-1925 and d216-0939 most likely originates from the foreground material and the surrounding disk, respectively. The angle of the disk inclination is found to be mainly responsible for the difference of the optical depth of the water ice among the five young stars. Our results suggest that there is a critical inclination angle between 65deg and 75deg for the circumstellar disk where the water ice absorption becomes strong. The average density at the disk surface of d216-0939 was found to be 6.38x10^(-18) g cm^(-3). The water ice absorption band in the d216-0939 disk is remarkable in that the maximum optical depth of the water ice band is at a longer wavelength than detected before. It indicates that the primary carrier of the feature is purely crystallized water ice at the surface of the d216-0939 disk with characteristic size of ~0.8um, which suggests grain growth. This is the first direct detection of purely crystallized water ice in a silhouette disk.
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