喷泉星云周围的大坝？用VISIR/VLT空间分辨IRAS16342-3814的尘埃壳层
A dam around the Water Fountain Nebula? The dust shell of IRAS16342-3814 spatially resolved with VISIR/VLT
摘要：
无论是通过校准快速的恒星风，还是通过中心系统中的吸积驱动喷流，尘埃鸟居或稳定的圆盘可能是形成PNE的关键因素。我们研究了非常年轻的原行星状星云IRAS 16342 -3814（也称为喷泉星云）中的尘埃分布，该星云以两个反射瓣的形状显示出强烈的双极特征，以及高速准直分子流出。我们使用新的中红外（MIR）仪器VISIR的甚大望远镜（VLT）在成像和光谱模式，波长从8到13微米。我们提出了第一个空间分辨的MIR观测的尘埃演化的恒星与VISIR，发现改进的空间分辨率相矛盾的椭圆形亮度分布在IRAS 16342的心脏以前的索赔：我们发现腰部区域是黑暗的，即使在MIR。我们表明，模糊的尘埃带，这是主要由无定形硅酸盐，填充角是非常大的，甚至可能接近一个球对称的超风中看到的OH/IR星。我们的结论是，在众多的最近尘埃盘检测后AGB星和PNE，IRAS 16342没有显示这种极端的赤道密度增强，至少不是在尺度的尘埃环境，借给对象的红外外观。相反，它似乎是所观察到的旋进喷流正在塑造一个球对称的AGB超风的遗迹中的双极性质。
英文摘要：
Either by collimating a fast stellar wind or by driving a jet via accretion in the central system, dusty torii or stable disks may be crucial ingredients for the shaping of PNe. We study the dust distribution in the very young Proto-Planetary Nebule (PPN) IRAS16342-3814, also known as the Water Fountain Nebula, which is known to show strong bipolar characteristics in the shape of two reflection lobes, and high-velocity collimated molecular outlfows. We use the new Mid-IR (MIR) instrument VISIR on the Very Large Telescope (VLT) both in imaging and spectroscopy mode at wavelengths from 8 to 13 micron. We present the first spatially resolved MIR observations of a dusty evolved star obtained with VISIR and find that the improved spatial resolution contradicts previous claims of an elliptical brightness distribution at the heart of IRAS16342: we find the waist region to be dark even in the MIR. We show that the filling angle of the obscuring dust lane, which is made mostly of amorphous silicates, is very large, possibly even close to a spherically symmetric superwind as seen in OH/IR stars. We conclude that, in contrast to the multitude of recent dusty-disk detections in Post-AGB stars and PNe, IRAS16342 does not show this extreme equatorial density enhancement, at least not on the scale of the dusty environment which lends the object its IR appearance. Rather, it appears that the observed precessing jets are shaping the bipolar nature in the remains of a spherically symmetric AGB superwind.
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