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Nat Commun. 2018 Jun 28;9(1):2534. doi: 10.1038/s41467-018-04767-8.

Astrometrically registered maps of H2O and SiO masers toward VX Sagittarii.

Author information

1
Astronomy Program, Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Korea.
2
Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon, 34055, Korea.
3
Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon, 34055, Korea. cho@kasi.re.kr.
4
Department of Astronomy, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul, 03722, Korea. cho@kasi.re.kr.
5
International Center for Radio Astronomy Research, M468, The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia.
6
OAN (IGN), Alfonso XII, 3 y 5, 28014, Madrid, Spain.
7
Shanghai Astronomical Observatory, Chinese Academy of Sciences, 200030, Shanghai, China.
8
Institute for Comprehensive Education, Kagoshima University, Korimoto 1-21-30, Kagoshima, 890-0065, Japan.
9
Department of Astronomy, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul, 03722, Korea.

Abstract

The supergiant VX Sagittarii is a strong emitter of both H2O and SiO masers. However, previous VLBI observations have been performed separately, which makes it difficult to spatially trace the outward transfer of the material consecutively. Here we present the astrometrically registered, simultaneous maps of 22.2 GHz H2O and 43.1/42.8/86.2/129.3 GHz SiO masers toward VX Sagittarii. The H2O masers detected above the dust-forming layers have an asymmetric distribution. The multi-transition SiO masers are nearly circular ring, suggesting spherically symmetric wind within a few stellar radii. These results provide the clear evidence that the asymmetry in the outflow is enhanced after the smaller molecular gas clump transform into the inhomogeneous dust layers. The 129.3 GHz maser arises from the outermost region compared to that of 43.1/42.8/86.2 GHz SiO masers. The ring size of the 129.3 GHz maser is maximized around the optical maximum, suggesting that radiative pumping is dominant.

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