Near-IR spectroscopy of planetary nebulae precursors ?
Near-IR spectroscopy of planetary nebulae precursors ?
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行星状星云前体的近红外光谱 ?
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
F. Prada
中科院分区：
文献类型：
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作者：
D. A. García;A. Manchado;P. Garcı́a;C. Dominguez;G. Conway;F. Prada
我们提出了近红外光谱的30个IRAS源最近确定为晚AGB星，后AGB星或早期PNe的样本。所得到的光谱集中在各种波长处，覆盖了氢分子v=1
8箭头0 S（1）2.122 μ m和v=2$ $
8 ~ 1 S（1）2.248 μ m发射谱线，Br γ、Pf γ和Br α复合谱线分别为2.166 μ m、3.741 μ m和4.052 μ m，CO[v= 2.248 μ m]发射谱线为2.052 μ m
[ightarrow$0]第一泛音带头为2.294 μ m。由于这些观测结果，我们首次在其中9个来源中检测到分子氢发射，并证实了Weintraub等人先前的检测结果（[CITE]）。这将在分子氢中检测到的原PNe总数从4增加到13。在大多数情况下，正的探测也显示出氢的复合谱线的发射（除了IRAS 17150-3224），这表明分子氢发射的开始发生在后AGB阶段，在星云电离之前不久。当氢分子被荧光激发时，发现探测率与中心星星的演化阶段直接相关，而不是与星云形态相关。当中心星星的温度足够高时，从快速演化的中心后AGB星星逃逸的紫外光子的吸收可以诱导荧光激发。相比之下，冲击激发的分子氢只在强双极原PNe中检测到，有时甚至在后AGB阶段的早期阶段。激波激发是AGB后快风与AGB期间喷出的慢风物质相互作用的结果。冲击激发的分子氢发射与所发现的双极性的强相关性证实了Kastner等人先前在演化的PNe中报道的结果。然而，我们的研究结果表明，这种相关性不存在的情况下，荧光激发的分子氢。
We present near-IR spectroscopy of a sample of 30 IRAS sources recently identified as late AGB stars, post-AGB stars or early PNe. The spectra obtained are centered at various wavelengths covering the molecular hydrogen $v=1$ $
ightarrow $0 S(1) 2.122 μ m and $v=2$ $
ightarrow$1 S(1) 2.248 μ m emission lines, the recombination lines of hydrogen Br γ 2.166 μ m, Pf γ 3.741 μ m and Br α 4.052 μ m, and the CO[ $v=2$ $
ightarrow$0] first overtone bandhead at 2.294 μ m. As a result of these observations we have detected molecular hydrogen emission for the first time in 9 of these sources and confirmed a previous detection by Weintraub et al. ([CITE]). This increases from 4 to 13 the total number of proto-PNe detected in molecular hydrogen. In most cases, the positive detections also show emission in the recombination lines of hydrogen (with the exception of IRAS 17150-3224) indicating that the onset of molecular hydrogen emission takes place in the post-AGB phase, very shortly before the nebula becomes ionized. When the molecular hydrogen is fluorescence-excited the detection rate is found to be directly correlated with the evolutionary stage of the central star, rather than with the nebular morphology. When the temperature of the central star is hot enough, fluorescence excitation can be induced by the absorption of UV photons escaping from the rapidly evolving central post-AGB star. In contrast, shock-excited molecular hydrogen is detected only in strongly bipolar proto-PNe, sometimes even at an early stage in the post-AGB phase. Shock excitation is the consequence of the interaction of the fast post-AGB wind with the slow wind material ejected during the AGB. The strong correlation of shock-excited molecular hydrogen emission with bipolarity found confirms the result previously reported by Kastner et al. ([CITE]) in evolved PNe. However, our results show that this correlation does not exist in the case of fluorescence-excited molecular hydrogen.