arXiv 2007.123102020-07-24astro-ph.GA

狭缝结构对空间分辨行星状星云H $_2$ 1-0~S（1）/Br $γ$线比的影响

The Effect of the Slit Configuration on the H$_2$ 1-0~S(1) to Br$γ$ Line Ratio of Spatially Resolved Planetary Nebulae

Isabel Aleman

备注：: Accept for publication in MNRAS. 12 pages, 7 figures, 2 tables
DOI：: 10.1093/mnras/staa2174

摘要：

H $_2$ 1-0~S（1）/Br $γ$比值（R（Br $γ$））用于行星状星云（PNe）分子含量的许多研究。由于这些谱线产生于不同的区域，光谱观测中使用的狭缝配置可能对它们的比率有重要影响。在这项工作中，观测和数值模拟被用来证明和量化这种影响在PNe。该研究旨在帮助解释观测结果并将其与模型进行比较。分析表明，当狭缝包含整个星云时，观测到的R（Br $γ$）比值仅达到0.3。只有当狭缝覆盖H $_2$峰值发射周围的有限区域时，才能获得高于该值的值，然后使Br $γ$发射最小化。数值模拟结果表明，当考虑到狭缝结构的影响时，光电离模型可以再现PNe中所观察到的R（Br $γ$）的整个范围，以及上述行为。因此，需要冲击来解释R（Br $γ$）的较高值的论点是无效的。因此，该比率不是文献中所建议的H $_2$激发机制的良好指标。

英文摘要：

The H$_2$ 1-0~S(1)/Br$γ$ ratio (R(Br$γ$)) is used in many studies of the molecular content in planetary nebulae (PNe). As these lines are produced in different regions, the slit configuration used in spectroscopic observations may have an important effect on their ratio. In this work, observations and numerical simulations are used to demonstrate and quantify such effect in PNe. The study aims to assist the interpretation of observations and their comparison to models. The analysis shows that observed R(Br$γ$) ratios reach only values up to 0.3 when the slit encompasses the entire nebula. Values higher than that are only obtained when the slit covers a limited region around the H$_2$ peak emission and the Br$γ$ emission is then minimised. The numerical simulations presented show that, when the effect of the slit configuration is taken into account, photoionization models can reproduce the whole range of observed R(Br$γ$) in PNe, as well as the behaviour described above. The argument that shocks are needed to explain the higher values of R(Br$γ$) is thus not valid. Therefore, this ratio is not a good indicator of the H$_2$ excitation mechanism as suggested in the literature.

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