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arXiv 0803.1624astro-ph
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NGC 7027毫米波段谱线测量

A spectral line survey of NGC 7027 at millimeter wavelengths

Yong Zhang, Sun Kwok, Dinh-V-Trung

摘要:

本文报道了最近利用亚利桑那射电天文台(ARO)12米望远镜和海因里希赫兹亚毫米波望远镜(SMT)对行星状星云(PN)NGC 7027进行的毫米波谱线观测。在71- 111 GHz、157- 161 GHz和218- 267 GHz的频率范围内获得了光谱,其典型灵敏度为rms<8 mK。共检测到67条谱线,其中21条被确定为8种分子,32条与氢和氦的复合线,14条未被确定。由于CO、其它中性分子、分子离子以及H+和He+复合的发射谱线宽度不同,因此利用谱线强度和谱线轮廓研究了NGC 7027中性包层的物理条件和化学过程。柱密度和相对于H2的所观察到的分子物种的丰度分数计算和比较与化学模型的预测。我们发现NGC 7027中N2 H+丰度过高,而CS和HNC丰度不足,这表明X射线辐射和冲击波可能在年轻PN的热分子包层化学中起重要作用。

英文摘要:

We report on a recent spectral line survey of the planetary nebula (PN) NGC 7027 using the Arizona Radio Observatory (ARO) 12m telescope and the Heinrich Hertz Submillimeter Telescope (SMT) at millimeter wavelengths. The spectra covering the frequency ranges 71--111GHz, 157--161GHz, and 218--267GHz were obtained with a typical sensitivity of rms<8mK. A total of 67 spectral lines are detected, 21 of which are identified with 8 molecular species, 32 with recombination lines from hydrogen and helium, and 14 remains unidentified. As the widths of emission lines from CO, other neutral molecules, molecular ions, as well as recombination of H+ and He+ are found to be different with each other, the line strengths and profiles are used to investigate the physical conditions and chemical processes of the neutral envelope of NGC 7027. The column densities and fractional abundances relative to H2 of the observed molecular species are calculated and compared with predictions from chemical models. We found evidence for overabundance of N2H+ and underabundance of CS and HNC in NGC 7027, suggesting that X-ray emission and shock wave may play an important role in the chemistry of the hot molecular envelope of the young PN.

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