CO in the C1 globule of the Helix nebula with ALMA
CO in the C1 globule of the Helix nebula with ALMA
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DOI：
10.1093/mnras/stz3026
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发表时间：
2019-10
影响因子：
4.8
通讯作者：
M. Andriantsaralaza;A. Zijlstra;Adam Avison The University of Manchester;U. O. H. Kong;UK Atacama Large Millimetersubmillimeter
中科院分区：
文献类型：
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作者：
M. Andriantsaralaza;A. Zijlstra;Adam Avison The University of Manchester;U. O. H. Kong;UK Atacama Large Millimetersubmillimeter
我们提出并分析了12 CO，13 CO和C18 O（2-1）阿尔马观测的C1球状星云内，以确定其物理性质。我们的研究结果证实了具有多峰结构的小球的分子本质。12 CO谱线具有很高的光学深度τ φ 10。12 C/13 C <$10和16 O/18 O <$115比值与富碳AGB星的预期同位素比值不一致。假设12 CO的光学厚度被低估了，我们可以找到一个一致的适合的初始质量为2兆赫兹。我们得到C1球的分子量为$\sim 2\，\times 10^{-4}\，\mbox{M}_\odot$，这比文献中的质量要高得多。结块可能在结的高分子量中起作用。讨论了尾巴的起源。我们的研究结果表明，最可能的模型似乎是阴影。结的运动学和分子形态与风扫模型不一致，光蒸发模型本身不足以解释小球的性质。我们提出了一个综合的模型，其中的光蒸发，流，阴影模型的影响都被认为是在尾部成形过程中。
We present and analyse 12CO, 13CO, and C18O(2–1) ALMA observations of the C1 globule inside the Helix nebula in order to determine its physical properties. Our findings confirm the molecular nature of the globule with a multipeak structure. The 12CO line has a high optical depth τ ∼10. The derived 12C/13C∼10 and 16O/18O∼115 ratios are not in agreement with the expected isotopic ratios of carbon-rich AGB stars. Assuming that the 12CO optical depth has been underestimated, we can find a consistent fit for an initial mass of 2 M⊙. We obtain a molecular mass of $\sim 2\, \times 10^{-4}\, \mbox{M}_\odot$ for the C1 globule, which is much higher than its mass in the literature. Clumping could play a role in the high molecular mass of the knot. The origin of the tail is discussed. Our findings show that the most probable model appears to be shadowing. The kinematics and molecular morphology of the knot are not consistent with a wind-swept model and the photoevaporation model alone is not enough to explain the nature of the globule. We propose an integrated model where the effects of the photoevaporation, the stream, and shadowing models are all considered in the tail shaping process.