First-epoch VSOP observation of 3C 380: Kinematics of the parsec-scale jet

The space-VLBI mission VSOP provides high-quality imaging capabilities to i nvestigate fine structures in quasar jets. We report on the first-epoch VSO P observation of the superluminal quasar 3C: 380 at lambda6 cm. A high-qual ity image with a dynamic range of 1:1200 at a resolution of 0.74 mas x 0.36 mas reveals precise structure along the pc-scale jet. Components C2, A, an d F, have been identified with those in previous ground-VLBI observations, and an apparent superluminal motion has been confirmed. We find a very stra ight motion with a constant apparent velocity for components A and F. Each motion vector is almost parallel to each position vector. This suggests a b allistic ejection from the core. In spite of better position accuracy than previous ground-VLBI observations, we cannot confirm any evidence of accele ration or changes of the position angle which were reported in Polatidis an d Wilkinson (1998, AAA 069.159.023). We confirmed that the bent jet structu re has kept its similarity and direction, compared with previous images. Th is suggests an oblique shock in relativistic flow rather than the Kelvin-He lmholtz instability.