用CARMA 0.25角秒角分辨率分子观测探测AGB星IRC +10216的复杂尘埃形成区
The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations
摘要：
我们目前的低光谱分辨率分子干涉观测在1.2毫米获得的毫米波天文学研究组合阵列（CARMA）对富C AGB星IRC+10216。我们绘制了几条线的发射的SiS，H13 CN，SiO，和SiC 2的基态和第一激发振动态的高角分辨率为0.25 arcsec。这些观测使我们能够部分地分辨出距离恒星小于50恒星半径（R*）的包层的辐射，在那里恒星风主要是加速的。分子发射的结构已被建模与三维辐射传输代码。用一组排列在5 ~ 20 R* 之间的脉泽发射弧最好地再现了SiS（v=0，J=14-13）线的发射。H13 CN相对于H2的丰度从1-5 R* 下的8 e-7降低到20 R* 下的3e-7。在1 ~ 5 R* 之间的壳状区域中，SiO的观测值用丰度<2 e-8来解释。此时，SiO丰度急剧增加，直至（2-3）e-7。在20 ~ 50 R* 之间，SiO的振动温度在正东北方向增加2倍。SiC 2在恒星表面形成，其丰度为8 e-7，在20 R* 时下降到8 e-8，可能是由于尘埃颗粒的耗尽。在H13 CN，SiO和SiC 2的丰度分布中发现了几种不对称性，它们在信封的探索区域中定义了三个显着的方向（东北，西南偏南和东南）。这些分子的红移和蓝移发射之间存在一些差异，表明它们的丰度分布沿视线存在额外的不对称性。
英文摘要：
We present low spectral resolution molecular interferometric observations at 1.2 mm obtained with the Combined Array for Research in Millimetre-wave Astronomy (CARMA) towards the C-rich AGB star IRC+10216. We have mapped the emission of several lines of SiS, H13CN, SiO, and SiC2 in the ground and first excited vibrational states with a high angular resolution of 0.25 arcsec. These observations have allowed us to partially resolve the emission of the envelope at distances from the star <50 stellar radii (R*), where the stellar wind is mainly accelerated. The structure of the molecular emission has been modelled with a 3D radiation transfer code. The emission of line SiS(v=0,J=14-13) is best reproduced with a set of maser emitting arcs arranged between 5 and 20 R*. The abundance of H13CN with respect to H2 decreases from 8e-7 at 1-5 R* to 3e-7 at 20 R*. The SiO observations are explained with an abundance <2e-8 in the shell-like region between 1 and 5 R*. At this point, the SiO abundance sharply increases up to (2-3)e-7. The vibrational temperature of SiO increases by a factor of 2 due North-East between 20 and 50 R*. SiC2 is formed at the stellar surface with an abundance of 8e-7 decreasing down to 8e-8 at 20 R* probably due to depletion on to dust grains. Several asymmetries are found in the abundance distributions of H13CN, SiO, and SiC2 which define three remarkable directions (North-East, South-Southwest, and South-East) in the explored region of the envelope. There are some differences between the red- and blue-shifted emissions of these molecules suggesting the existence of additional asymmetries in their abundance distributions along the line-of-sight.
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