ALMA对NGC 6302致密分子区的高空间分辨率观测
ALMA high spatial resolution observations of the dense molecular region of NGC 6302
摘要：
双极行星状星云形成背后的机制仍然知之甚少。精确地追踪后AGB恒星的富含分子的赤道区域，可以对工作中的喷射机制提供有价值的见解。利用ALMA波段7干涉图研究了行星状星云NGC 6302致密分子区的物理条件、结构和速度场。$^{12}$ CO和$^{13}$ CO J=3-2 ALMA数据的高空间分辨率允许对喷出物的几何形状进行前所未有的详细分析。我们用SHAPE软件建立了分子区域的空间运动学模型，并用SHAPEMOL插件进行了详细的激发和辐射传递的非LTE计算。我们发现，分子区域由一个巨大的环，其中出现了一个系统的瓣壁碎片，并包围在光学可见的瓣的基础。该区域的一般属性与以前的作品是一致的，虽然更大的空间分辨率的数据允许一个非常详细的描述。我们确认分子区域的质量为0.1 M $_{\odot}$。此外，我们报告了一个以前未检测到的成分在星云赤道，一个内部，年轻的环倾斜$\sim$ 60 $^\circ$相对于主环，显示出一个特征半径为7.5 $\times$ 10 $^{16}$厘米，质量为2.7 $\times$ 10 $^{-3}$ M $_{\odot}$，和对应的光学图像的星云。这个内环与西北光学叶的运动学年龄相同，这意味着它大约在同一时间喷出，在大部分分子环状区域喷出之后数百年。我们讨论了一系列的事件导致形成的分子和光学星云，并简要地推测这个有趣的内环的起源。
英文摘要：
The mechanism behind the shaping of bipolar planetary nebulae is still poorly understood. Accurately tracing the molecule-rich equatorial regions of post-AGB stars can give valuable insight into the ejection mechanisms at work. We investigate the physical conditions, structure and velocity field of the dense molecular region of the planetary nebula NGC 6302 by means of ALMA band 7 interferometric maps. The high spatial resolution of the $^{12}$CO and $^{13}$CO J=3-2 ALMA data allows for an analysis of the geometry of the ejecta in unprecedented detail. We built a spatio-kinematical model of the molecular region with the software SHAPE and performed detailed non-LTE calculations of excitation and radiative transfer with the SHAPEMOL plug-in. We find that the molecular region consists of a massive ring out of which a system of fragments of lobe walls emerge and enclose the base of the lobes visible in the optical. The general properties of this region are in agreement with previous works, although the much greater spatial resolution of the data allows for a very detailed description. We confirm that the mass of the molecular region is 0.1 M$_{\odot}$. Additionally, we report a previously undetected component at the nebular equator, an inner, younger ring inclined $\sim$60$^\circ$ with respect to the main ring, showing a characteristic radius of 7.5$\times$10$^{16}$ cm, a mass of 2.7$\times$10$^{-3}$ M$_{\odot}$, and a counterpart in optical images of the nebula. This inner ring has the same kinematical age as the northwest optical lobes, implying it was ejected approximately at the same time, hundreds of years after the ejection of the bulk of the molecular ring-like region. We discuss a sequence of events leading to the formation of the molecular and optical nebulae, and briefly speculate on the origin of this intriguing inner ring.
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