Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001crlj...48...31i&link_type=abstract
Journal of the Communications Research Laboratory. Special Issue: Large Aperture Radio Telescopes at Kashima Space Research Cent
Astronomy and Astrophysics
Astrophysics
Stellar Evolution, Water Masers, Emission, Cosmic Rays, Astrometry, Astrophysics, Estimating, High Frequencies, Massive Stars, Semiregular Variable Stars, Solar System, Star Formation
Scientific paper
Cosmic maser emission from water vapors has been observed at an early stage of birth and at the final stage of death in stellar evolution. We have observed such water masers using the Japanese domestic VLBI network for astronomy (J-Net) and revealed in detail the kinematics of water masers around protostars and evolved stars. The results of these observations are summarized as follows. (1) Systematic radial-velocity drifts of water maser features with time were found around the semiregular variable star RT Vir. This phenomenon, first discovered here, indicates acceleration motion of mass-loss flow around the star. (2) Rotation-infall motions around the protostar IRAS 16923-2422 were revealed on a solar-system scale with water masers. These motions indicate a dynamical infall of materials onto the protostar on a scale down to a few tens of AU. (3) A large number of proper motions of water maser features were measured in the massive-star forming region W51 North. The 3D kinematics of an outflow from W51 North was determined and the distance to W51 North was estimated directly as 6.7+2.1 kpc. (4) A study of high precision astrometry for maser sources was begun to advance stellar astrophysics. In this study, the phase-referencing technique by a fast antenna-switching method was applied to water masers around the supergiant star S Per and the continuum source KR 143. Although the accuracy of relative astrometry for the maser sources is limited to 1 mas at present, fringe-phase fluctuation due to the atmosphere can be compensated effectively in a relatively high frequency band of 22.2 GHz.
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