Santander-García M, Bujarrabal V, Alcolea J, Castro-Carrizo A, Sánchez Contreras C, Quintana-Lacaci G, Corradi R L M, Neri R
Instituto de Ciencia de Materiales de Madrid (CSIC), E-28049, Madrid, Spain; Observatorio Astronómico Nacional (IGN), C/ Alfonso XII 3, E-28014, Madrid, Spain.
Observatorio Astronómico Nacional (IGN), Ap. de Correos 112, E-28803, Alcalá de Henares, Madrid, Spain.
Astron Astrophys. 2017 Jan;597. doi: 10.1051/0004-6361/201629288. Epub 2016 Dec 19.
The mechanism behind the shaping of bipolar planetary nebulae is still poorly understood. It is becoming increasingly clear that the main agents must operate at their innermost regions, where a significant equatorial density enhancement should be present and related to the collimation of light and jet launching from the central star preferentially towards the polar directions. Most of the material in this equatorial condensation must be lost during the asymptotic giant branch as stellar wind and later released from the surface of dust grains to the gas phase in molecular form. Accurately tracing the molecule-rich regions of these objects can give valuable insight into the ejection mechanisms themselves.
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 CO and CO =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. Additionally, we report a previously undetected component at the nebular equator, an inner, younger ring inclined ~60° with respect to the main ring, showing a characteristic radius of 7.5×10 cm, a mass of 2.7×10 M, 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.
双极行星状星云形成背后的机制仍未得到很好的理解。越来越明显的是，主要作用因素必定在其最内部区域起作用，在该区域应该存在显著的赤道密度增强，并且这与光的准直以及从中心恒星优先向极向发射喷流有关。在渐近巨星分支阶段，这个赤道凝聚物中的大部分物质必定会以恒星风的形式损失，随后以分子形式从尘埃颗粒表面释放到气相中。准确追踪这些天体富含分子的区域能够为喷射机制本身提供有价值的见解。
我们借助阿塔卡马大型毫米/亚毫米波阵列（ALMA）7波段干涉图来研究行星状星云NGC 6302致密分子区域的物理条件、结构和速度场。
一氧化碳（CO）和一氧化碳J = 3 - 2的ALMA数据具有高空间分辨率，这使得我们能够以前所未有的详细程度分析喷射物的几何形状。我们使用SHAPE软件构建了分子区域的时空运动学模型，并使用shapemol插件对激发和辐射转移进行了详细的非局部热动平衡（non-LTE）计算。
我们发现分子区域由一个巨大的环组成，从这个环中出现了一系列叶壁碎片系统，并包围了在光学波段可见的叶瓣底部。尽管数据具有更高的空间分辨率，从而能够进行非常详细的描述，但该区域的一般特性与之前的研究结果一致。我们证实分子区域的质量为0.1个太阳质量（M☉）。此外，我们报告了在星云赤道处一个先前未被探测到的成分，这是一个内部的、较年轻的环，相对于主环倾斜约60°，其特征半径为7.5×10¹⁵厘米，质量为2.7×10⁻³M☉，并且在星云的光学图像中有对应物。这个内环与西北光学叶瓣具有相同的运动学年龄，这意味着它大约是在同一时间被喷射出来的，即在大部分分子环状区域被喷射出来数百年之后。我们讨论了导致分子星云和光学星云形成的一系列事件，并简要推测了这个有趣的内环的起源。
