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1
VLBI Monitoring of the Sub-parsec-scale Jet in the Radio Galaxy 3C 66B at 22 GHz

Sudou, Hiroshi,Iguchi, Satoru,Zhao, Guang-Yao American Astronomical Society 2017 The Astrophysical journal Vol.841 No.2
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<P>We present measurements of the proper motion of the sub-parsec scale jet at 22 GHz in the nearby FR I galaxy 3C 66B. Observations were made using Very Long Baseline Array (VLBA) at six epochs over four years. A phase-referencing technique was used to improve the image quality of the weak and diffuse jet components. We find that the inner knots are almost stationary, although one of them was expected to be detected with an apparent speed of 0.2 mas yr(-1), according to 8 GHz monitoring at the same observation epochs. Clear flux variations are not observed in the core at 22 GHz; in contrast, clear flux enhancement is observed in the core at 8 GHz. We discuss a possible explanation: if the jet has helical structure, the viewing angles of the jet at 8 and 22 GHz differ by a few degrees, if the jet direction is almost along our line of sight. Although these results may imply the existence of a two-zone jet, which has been suggested in certain radio galaxies, it cannot explain the fact that the jet at the higher frequency is slower than that at the lower frequency.</P>
2
TIME VARIATIONS OF THE RADIAL VELOCITY OF H2O MASERS IN THE SEMI-REGULAR VARIABLE R CRT

Hiroshi Sudou,Motoki Shiga,Toshihiro Omodaka,Chihiro Nakai,Kazuki Ueda,Hiroshi Takaba 한국천문학회 2017 Journal of The Korean Astronomical Society Vol.50 No.6
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  ScienceON
  
  코리아스칼라
H$_2$O maser emission {at 22 GHz} in the circumstellar envelope is one of the good tracers of detailed physics and inematics in the mass loss process of asymptotic giant branch stars. Long-term monitoring of an H$_2$O maser spectrum with high time resolution enables us to clarify acceleration processes of the expanding shell in the stellar atmosphere. We monitored the H$_2$O maser emission of the semi-regular variable R Crt with the Kagoshima 6-m telescope, and obtained a large data set of over 180 maser spectra over a period of 1.3 years with an observational span of a few days. Using an automatic peak detection method based on least-squares fitting, we exhaustively detected peaks as significant velocity components with the radial velocity on a 0.1 km s$^{-1}$ scale. This analysis result shows that the radial velocity of red-shifted and blue-shifted components exhibits a change between acceleration and deceleration on the time scale of a few hundred days. These velocity variations are likely to correlate with intensity variations, in particular during flaring state of H$_2$O masers. It seems reasonable to consider that the velocity variation of the maser source is caused by shock propagation in the envelope due to stellar pulsation.However, it is difficult to explain the relationship between the velocity variation and the intensity variation only from shock propagation effects. We found that a time delay of the integrated maser intensity with respect to the optical light curve is about 150 days.
3
MULTI-EPOCH MULTI-FREQUENCY VLBI STUDY OF THE PARSEC-SCALE JET IN THE BLAZAR 3C 66A

Zhao, Guang-Yao,Chen, Yong-Jun,Shen, Zhi-Qiang,Sudou, Hiroshi,Iguchi, Satoru American Institute of Physics 2015 The Astronomical journal Vol.149 No.2
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<P>We present observational results of the &ggr;-ray blazar 3C 66A at 2.3, 8.4, and 22 GHz at four epochs during 2004–2005 with the VLBA. The resulting images show an overall core-jet structure extending roughly to the south, with two intermediate breaks occurring in the region near the core. By model-fitting to the visibility data, the northmost component, which is also the brightest, is identified as the core according to its relatively flat spectrum and its compactness. Combining our results with previous results to investigate the proper motions of the jet components, we found the kinematics of 3C 66A to be quite complicated, with components of inward and outward, subluminal and superluminal motions all detected in the radio structure. The superluminal motions indicate strong Doppler boosting exists in the jet. The apparent inward motions of the innermost components last for at least 10 years and could not be caused by newborn components. A possible reason could be non-stationarity of the core due to opacity change.</P>