Proper motion of the extremely high velocity SiO J=2 -> 1 emission in L1448

We report the first measurements of proper motions in a molecular outflow b y using interferometric rotational line observations. We observed and mappe d with the BIMA millimeter array the extremely high velocity (EHV) SiO J = 2 --> 1 emission associated with the L1448 molecular outflow. Comparisons w ere made with the Plateau de Pure interferometer maps carried out 8.5 yr ea rlier. We obtained proper motions of up to 0."12 yr(-1), which imply absolu te velocities of 180 km s(-1) and an outflow inclination of 21 degrees to t he 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 p owerful interferometric arrays, the combination of high spectral and angula r resolution with high sensitivity will permit a detailed three-dimensional picture of the kinematics of molecular outflows.