A Spectrophotometric Survey of K-Band Emission Lines in Planetary Nebulae
A Spectrophotometric Survey of K-Band Emission Lines in Planetary Nebulae
复制标题
行星状星云 K 波段发射线的分光光度测量
DOI：
10.1086/500050
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
K. Bartig
中科院分区：
文献类型：
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作者：
L. Likkel;H. Dinerstein;D. Lester;A. Kindt;K. Bartig
本文介绍了McDonald天文台长狭缝近红外光谱仪在2 μm（K波段）光谱区对16个行星状星云的观测结果。一般来说，我们的光谱中最强的特征是H I，He I和（在某些情况下）He II的复合线。一半的样品显示振动激发的H2的发射。一些观察到的PN（例如，M 1-13）显示了受冲击的热化气体的H2线比率特征，而其他（例如，BD +30 3639）具有介于纯辐射（UV）和冲击激发之间的比率，与致密材料的机制或UV照射的组合一致。我们的光谱J 900和M 1-13证实，公布的窄带图像跟踪的H2发射，我们发现，在SwSt 1的H2发射具有更大的空间范围比以前报道的。在IC 5117、SwSt 1和NGC 40中，我们探测到Dinerstein在2001年发现的[Kr III] 2.199 μm线，其强度表明氪相对于太阳丰度是富集的，在NGC 40中最为明显。我们还检测到几条线从3G长期的[Fe III]在Vy 2-2，SwSt 1，和轻微的Cn 3-1。[Kr III]和[Fe III]线的波长接近H2跃迁，这通常被用作UV激发的诊断，因为它们来自更高的振动激发能级（v = 2，3）。对于中等光谱分辨率，R ≤ 600，这些谱线可能与相应的H2谱线混合，甚至被误认为是H2谱线，导致对H2发射的误解。Kr和Fe星云发射线的强度都可以在特殊情况下增强，Kr是因为在祖星星中的核合成自富集，Fe是由于初始尘埃凝结效率低下或形成后尘埃的部分破坏，导致大部分元素铁停留在气相中。
We present observations of 16 planetary nebulae (PNs) in the 2 μm (K band) spectral region, obtained with a long-slit near-infrared spectrometer at McDonald Observatory. In general, the strongest features in our spectra are recombination lines of H I, He I, and (in some cases) He II. Half the sample shows emission from vibrationally excited H2. Some of the observed PNs (e.g., M 1-13) display H2 line ratios characteristic of shocked, thermalized gas, while others (e.g., BD +30 3639) have ratios intermediate between pure radiative (UV) and shock excitation, consistent with either a combination of the mechanisms or UV illumination of dense material. Our spectra of J900 and M 1-13 confirm that published narrowband images trace the H2 emission, and we find that the H2 emission in SwSt 1 has a larger spatial extent than previously reported. In IC 5117, SwSt 1, and NGC 40 we detect the [Kr III] 2.199 μm line identified by Dinerstein in 2001, with strengths indicating that krypton is enriched relative to the solar abundance, most markedly so in NGC 40. We also detect several lines from the 3G term of [Fe III] in Vy 2-2, SwSt 1, and marginally in Cn 3-1. The [Kr III] and [Fe III] lines fall near in wavelength to H2 transitions, which are often used as diagnostics for UV excitation because they arise from higher vibrationally excited levels (v = 2, 3). For moderate spectral resolving power, R ≤ 600, these lines may be blended with, or even mistaken for, the corresponding H2 lines, leading to misinterpretation of the H2 emission. The strength of both the Kr and Fe nebular emission lines can be enhanced by special circumstances, Kr because of nucleosynthetic self-enrichment in the progenitor star and Fe due to inefficient initial dust condensation or partial destruction of the dust after formation, causing a larger fraction of the elemental iron to reside in the gas phase.