1992 Fiscal Year Final Research Report Summary
Observations of Late-Type Stars with mm-VLBI
| Project/Area Number |
02452015
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Astronomy
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| Research Institution | National Astronomical Observatory(NAO) |
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Principal Investigator |
UKITA Nobuharu NAO, Div. of Radio Astron. associate professor, 電波天文学研究系, 助教授 (20184989)
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| Co-Investigator(Kenkyū-buntansha) |
MIKOSHIBA H NAO, Nobeyama Radio Obs. assistant, 野辺山宇宙電波観測所, 助手 (50249942)
TSUBOI M NAO, Div. of Radio Astron. assistant, 電波天文学研究系, 助手 (10202186)
高羽 浩 郵政省通信総合研究所, 関東支所, 研究官
SASAO T NAO, Div. of Earth Rotation professor, 地球回転研究系, 教授 (20000177)
INOUE M NAO, Div. of Radio Astron. associate professor, 電波天文学研究系, 助教授 (10151622)
TSUBOI M Comm.Research Lab., KSRC research associate
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| Project Period (FY) |
1990 – 1992
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| Keywords | VLBI / variable star / maser / mass-loss / position astronomy / proper motion / group delay / bandwidth synthesis |
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| Research Abstract |
VLBI observations of the two SiO maser lines, the nu=1 and nu=2,J=1-0,for three late-type stars have been made with the Kashima 34-m and Nobeyama 45-m radio telescopes. We found that the maser emissions come from a ring-like structure with diameters comparable to those of a central star for mu Cep and W Hya. The diameter of the ring structure seen around VY CMa was several times larger than that estimated for the central star. No clear relations have been found between the spatial distributions of maser spots and their radial velocities. These facts suggest that the maser emission arises from an extended atmosphere where material may be nearly stationary and that maser amplification paths are toward the limb rather than along the line of sight to the central star. Our observations also revealed that the corresponding velocity components of the nu=1 and nu=2 masers have the same distributions. Our results strongly suggest that an infrared line-overlapping plays an important role in the SiO maser mechanism. Our results also imply that it is possible to measure a group delay with a bandwidth synthesis technique using the SiO J=1-0 maser lines in the vibrational states nu=1 and nu=2, which are separated by 300 MHz in frequency. This new method allows us to determine the positions, and then the proper motions, of these stars with absolute positional accuracies of milliarcseconds. We have tried to analyze group delays for these stars, but some technical problems prevented us to measure with such an accuracy.
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