Proper Motion of the Extremely High Velocity S[CLC]i[/CLC]O [ITAL]J[/ITAL] = 2 → 1 Emission in L1448

We report the first measurements of proper motions in a molecular outflow by using interferometric rotational line observations. We observed and mapped with the BIMA millimeter array the extremely high velocity (EHV) SiO J = 2 → 1 emission associated with the L1448 molecular outflow. Comparisons were made with the Plateau de Bure interferometer maps carried out 8.5 yr earlier. We obtained proper motions of up to 0 12 yr -1 , which imply absolute velocities of 180 km s -1 and an outflow inclination of 21° to the plane of the sky, in agreement with previous modeling of the CO emission. These proper motions suggests that the EHV emission in L1448 has a short timescale. These results strongly suggest that with the new generation of powerful interferometric arrays, the combination of high spectral and angular resolution with high sensitivity will permit a detailed three-dimensional picture of the kinematics of molecular outflows.