IRS 7 is an M red supergiant star which is located at $5".5$ north of Sagittarius A$^\ast$. We detected firstly the continuum emission at 340 GHz of IRS 7 using ALMA. The total flux density of IRS 7 is $S_\nu=448\pm45 \mu$Jy. The flux density indicates that IRS 7 has a photosphere radius of $R=1170\pm60 ~R_\odot$, which is roughly consistent with the previous VLTI measurement. We also detected a shell like feature with north extension in the H30$\alpha$ recombination line by ALMA. The electron temperature and electron density of the shell like structure are estimated to be $\bar{T}^\ast_{\mathrm e}=4650\pm500$ K and $\bar{n}_{\mathrm e}=(6.1\pm0.6)\times10^4$ cm$^{-3}$, respectively. The mass loss rate is estimated to be $\dot{m} \sim 1\times 10^{-4} M_\odot$ yr$^{-1}$, which is consistent with a typical mass loss rate of a pulsating red supergiant star with $M=20-25 M_\odot$. The kinematics of the ionized gas would support the hypothesis that the shell like structure made by the mass loss of IRS 7 is supersonically traveling in the ambient matter toward the south. The brightened southern half of the structure and the north extension would be a bow shock and a cometary-like tail structure, respectively.

中文翻译：

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ALMA 对银河系中心冷星 IRS 7 的亚毫米探测

这与典型的脉动红超巨星质量损失率一致，$M=20-25 M_\odot$。电离气体的运动学将支持以下假设：由 IRS 7 的质量损失形成的壳状结构在周围物质中以超音速向南行进。结构变亮的南半部和北延伸部将分别是弓形激波和彗星状尾部结构。