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arXiv 1903.07129astro-ph.SR
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NOEMA绘制了红超巨星$μ$ Cep的CO $J = 2-1$环境

NOEMA maps the CO $J = 2-1$ environment of the red supergiant $μ$ Cep

M. Montargès, W. Homan, D. Keller, N. Clementel, S. Shetye, L. Decin, G. M. Harper, P. Royer, J. M. Winters, T. Le Bertre, A. M. S. Richards

备注：
15 pages, 4 tables, 9 figures. 2nd version : one co-author removed and acknowledgement updated (consistent with erratum https://doi.org/10.1093/mnras/stz1006)
发表信息：
MNRAS 485, 2417 (2019)
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摘要：

红超巨星被气体和尘埃环绕的星周环境所包围，这是由于它们的质量损失将重元素扩散到星际介质中而造成的。这个包层的结构和动力学对于理解驱动红超巨星质量损失的过程和前超新星喷出物的形成至关重要。我们用NOEMA干涉仪观测了红超巨星$μ$ ~Cep的CO $J = 2-1$线的辐射。在该线中，合成光束为$0.92 \times 0.72$ ~arcsec（$590 \times 462$ ~au，641~pc）。连续谱图只显示了恒星色球层的自由-自由辐射的未解决的贡献。连续扣除通道图揭示了一个非常不均匀和clusified拱星环境。特别是，我们在蓝色通道图中发现了一个明亮的CO团，与线中的中心源一样明亮，位于恒星西南1.80角秒处。在假设两个不同的恒定风速的径向速度的解投影后，使用3D辐射传输代码\textsc{lime}对观测进行建模，以导出不同结构的特性。我们确定，$μ$ ~Cep周围观察到的气体团块负责质量损失率为$(4.9 \pm 1.0) \times 10^{-7}~{\rm M}_\odot\,{\rm yr}^{-1}$，除了空间上无法分辨的风分量与估计的质量损失率为$2.0 \times 10^{-6}~{\rm M}_\odot\,{\rm yr}^{-1}$。因此，团块在$μ$ ~Cep的质量损失（$\ge 25 \%$）中具有重要作用。我们不能排除未解决的中心流出可能是由较小的未解决的团块。

英文摘要：

Red supergiant stars are surrounded by a gaseous and dusty circumstellar environment created by their mass loss which spreads heavy elements into the interstellar medium. The structure and the dynamics of this envelope are crucial to understand the processes driving the red supergiant mass loss and the shaping of the pre-supernova ejecta. We have observed the emission from the CO $J = 2-1$ line from the red supergiant star $μ$~Cep with the NOEMA interferometer. In the line the synthesized beam was $0.92 \times 0.72$~arcsec ($590 \times 462$~au at 641~pc). The continuum map shows only the unresolved contribution of the free-free emission of the star chromosphere. The continuum-subtracted channel maps reveal a very inhomogeneous and clumpy circumstellar environment. In particular, we detected a bright CO clump, as bright as the central source in the line, at 1.80~arcsec south-west from the star, in the blue channel maps. After a deprojection of the radial velocity assuming two different constant wind velocities, the observations were modelled using the 3D radiative transfer code \textsc{lime} to derive the characteristics of the different structures. We determine that the gaseous clumps observed around $μ$~Cep are responsible for a mass loss rate of $(4.9 \pm 1.0) \times 10^{-7}~{\rm M}_\odot\,{\rm yr}^{-1}$, in addition to a spatially unresolved wind component with an estimated mass-loss rate of $2.0 \times 10^{-6}~{\rm M}_\odot\,{\rm yr}^{-1}$. Therefore, the clumps have a significant role in $μ$~Cep's mass loss ($\ge 25 \%$). We cannot exclude that the unresolved central outflow may be made of smaller unresolved clumps.

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