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arXiv 2209.09052astro-ph.SRastro-ph.GA
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行星状星云NGC 7009短轴的双层壳

Double Shells of the Planetary Nebula NGC 7009 Minor Axis

Seong-Jae Lee, Siek Hyung, Masaaki Otsuka

备注：
15 pages, 9 figures, accepted for publication in ApJ
发表信息：
The Astrophysical Journal, 2022,
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摘要：

我们分析了用Keck HIRES观测到的椭圆行星状星云NGC 7009的短轴光谱，其中0.862 $"$ $\times$ 10 $"$狭缝位于距中心约7.5 $"$和10 $"$处，中心有0.862 $"$ $\times$ 14 $"$狭缝。从沿Keck HIRES狭缝长度的积分[SII] 6716/6731 μ m通量导出的平均密度表明密度范围为10 $^{3.7}$至10 $^{4.1}$ cm $^{-3}$，而从狭缝光谱图像导出的局部密度显示约10 $^{2.8}$ - 10 $^{4.6}$ cm $^{-3}$的较大局部密度变化：局部密度的变化远大于在视线上积分的值。由[SII]得到的主壳层和外壳层的膨胀率分别约为21.7和30.0 km $^{-1}$。[SII]谱线的运动学结果对应于两个壳层的最外区域，并且不代表整个PN，但与壳层气体中观察到的其他发射线密切相关。我们的结论是密度差导致的内壳层的形成，而电离状态的变化导致的外壳层的形成。我们认为，内壳层和外壳层是由两次连续的大抛射造成的。当这些壳层最初形成时，中心恒星的物理条件一定是不同的。

英文摘要：

We analyzed the minor axis spectra of the elliptical planetary nebula (PN) NGC 7009 observed with the Keck HIRES with a 0.862$"$ $\times$ 10$"$ slit placed at about $\sim$7.5$"$ and 10$"$ away from the center and a 0.862$"$ $\times$ 14$"$ slit at the center. The mean densities derived from the integrated [SII] 6716/6731Å, fluxes along the Keck HIRES slit length indicate a density range of 10$^{3.7}$ to 10$^{4.1}$ cm$^{-3}$, while the local densities derived from the slit spectral images show a large local density variation of about 10$^{2.8}$ - 10$^{4.6}$ cm$^{-3}$: local densities vary substantially more than values integrated over the line of sight. The expansion rates of the main and outer shells obtained by [SII] are about 21.7 and 30.0 kms$^{-1}$, respectively. The kinematic results of the [SII] spectral lines correspond to the outermost regions of the two shells and are not representative of the whole PN but are closely related to the other emission lines observed in the shell gas. We conclude that the density contrast leads to the formation of the inner shell, while the change in ionization state leads to the formation of the outer shell. We suggest that the inner main and outer shells result from two successive major ejections. The physical conditions of the central star must have been different when these shells first formed.

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