The optical spectrum of NGC 7009 - I. A low-excitation bright ring region on the major axis
The optical spectrum of NGC 7009 - I. A low-excitation bright ring region on the major axis
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NGC 7009 的光谱 - I. 长轴上的低激发亮环区域
DOI：
10.1093/mnras/273.4.958
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发表时间：
1995
影响因子：
4.8
通讯作者：
L. Aller
中科院分区：
文献类型：
--
作者：
S. Hyung;L. Aller
最近的观察表明，NGC 7009具有非常复杂的结构。利用Lick天文台的哈密尔顿梯形光谱仪，对NGC7009的长轴和短轴上亮环上的两个区域，波长范围为3650到10050Å的NGC7009的光谱进行了详细的高光谱分辨率观测。在本文中，我们只介绍长轴的结果。我们借助理论光电离模型对星云光谱进行了分析，得出以下结论：(I)这样的光致电离模型似乎能很好地符合明亮环中的发射；(Ii)这些结不太可能位于相对于观测者高度倾斜的轴上，这一观点是从运动学研究中引入的，其中这些结被认为是高度准直流出的副产品。NGC7009是富氧的，因为O/C比超过1。C、O和K的相对丰度似乎比太阳中的小；其他“金属”的丰度似乎与太阳的价值相当。在该模型的帮助下，哈密顿数据与以前的成像管扫描仪(ITS)数据的比较表明，NGC 7009中可能存在氮丰度的变化，这一结果与以前的工作人员获得的结果是一致的。
Recent observations suggest that NGC 7009 has a very complicated structure. Detailed high-spectral-resolution observations of the spectrum of NGC 7009 have been made for two regions in the bright ring on the major and minor axes, for the wavelength region 3650 to 10050 Å, using the Hamilton echelle spectrograph of the Lick Observatory. In this article we present only the results for the major axis. We have analysed the nebular spectra with aid of theoretical photoionization models and come to the following conclusions: (i) it appears that such a photoionization model can fit the emission reasonably well in the bright ring; (ii) it is unlikely that the knots lie along an axis that is highly inclined with respect to the observer, an idea which was introduced from kinematical studies, wherein the knots are considered as a by-product of highly collimated outflows.NGC 7009 is oxygen-rich because the O/C ratio exceeds 1. The relative abundances of C, O and K appear to be smaller than in the Sun; abundances of other ‘metals’ seem to be comparable with the solar values. With the help of the model, a comparison of the Hamilton data with the previous image-tube scanner (ITS) data suggests that a variation in nitrogen abundance may exist in NGC 7009, a result in harmony with that obtained by previous workers.