Sub-millimeter Detection of a Galactic Center Cool Star IRS 7 by ALMA

Abstract

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 $S_{\nu }=448\pm 45\mu$Jy. The flux density indicates that IRS 7 has a photosphere radius of $R=1170\pm 60R_{\odot }$, 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 ${\bar{T}}_{\mathrm{e}}^{\ast }=4650\pm 500$ K and ${\bar{n}}_{\mathrm{e}}=(6.1\pm 0.6)\times 10^4$ 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 $M=20-25M_{\odot }$. 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.

arXiv comment15 pages, 5 figures Accepted for publication in PASJ

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Cited by in corpus (5)

• Evidence of Deep Mixing in IRS 7, a Cool Massive Supergiant Member of the Galactic Nuclear Star Cluster
• X3: a high-mass Young Stellar Object close to the supermassive black hole Sgr~A*
• Mid-Infrared studies of dusty sources in the Galactic Center
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• MOLsphere and pulsations of the Galactic Center's red supergiant GCIRS 7 from VLTI/GRAVITY