用3D电离和形态学研究破译双极行星状星云Abell 14
Deciphering the bipolar planetary nebula Abell 14 with 3D ionization and morphological studies
摘要：
阿贝尔14是一个研究很少的天体，尽管被认为是一个重生的行星状星云。我们使用SHAPE和MOCASSIN代码对其三维形态和电离结构进行了详细的研究。我们发现Abell 14是一个高度演化的双极星云，其运动学年龄为$\sim$ 19,400年，距离为4千秒差距。高He丰度和N/O比表明5 $M_{\odot}$的祖先经历了第三次疏浚和热底部燃烧阶段。中央源的恒星参数显示，在白矮星冷却轨道附近有一颗处于高度演化阶段的恒星，这与重生的假设不一致。该星云显示出出乎意料的强[N I] $λ5200$和[O I] $λ6300$发射线，表明可能存在激波相互作用。阿贝尔14似乎是一小群高度进化的极端I型PNE的成员。该组的成员位于[N II]/H $α$与[S II]/H $α$诊断图上PNe区的左下角，其中也放置了冲击激发区/物体。它们中心恒星的低光度，加上星云的大体积，导致了非常低的光电离率，这使得即使在很小的速度下，也可以很容易地感知到激波相互作用的任何贡献。
英文摘要：
Abell 14 is a poorly studied object despite being considered a born again planetary nebula. We performed a detailed study of its 3D morphology and ionization structure using the SHAPE and MOCASSIN codes. We found that Abell 14 is a highly evolved, bipolar nebula with a kinematical age of $\sim$19,400 yr for a distance of 4 kpc. The high He abundance, and N/O ratio indicate a progenitor of 5 $M_{\odot}$ that has experienced the third dredge-up and hot bottom burning phases. The stellar parameters of the central source reveal a star at a highly evolved stage near to the white dwarf cooling track, being inconsistent with the born again scenario. The nebula shows unexpectedly strong [N I] $λ5200$ and [O I] $λ6300$ emission lines indicating possible shock interactions. Abell 14 appears to be a member of a small group of highly evolved, extreme Type-I PNe. The members of this group lie at the lower-left corner of the PNe regime on the [N II]/H$α$ vs. [S II]/H$α$ diagnostic diagram, where shock--excited regions/objects are also placed. The low luminosity of their central stars, in conjunction with the large physical size of the nebulae, result in a very low photo-ionization rate, which can make any contribution of shock interaction easily perceptible, even for small velocities.
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