DETECTION OF MAGNETOHYDRODYNAMIC SHOCKS IN THE L1551 OUTFLOW

We report the results Of CO J = 1 --> 0 mapping of portions of the blue outflow lobe of L1551 with approximately 7'' (N-S) x 4'' (E-W) resolution, obtained with the three element OVRO millimeter array. Comparison of our interferometer mosaic with lower resolution single-dish data shows that we resolve the strongest single-dish emission regions into filamentary structures, such as are characteristic of shock fronts mapped via their near-infrared H2 emission in other outflow sources. We detect a continuous velocity gradient across the brightest filamentary structure in our maps. The projected, deconvolved, FWHM of this feature is 1-2 x 10(16) cm, similar to that predicted in theoretical models of C-shocks. Combined with the velocity gradient, this suggests that the emission originates from within a magnetohydrodynamic shock front, possibly resulting from the interaction of a stellar wind with dense, ambient material. In contrast, the discontinuous J-shocks expected in regions with low or no magnetic field should have a thickness less-than-or-equal-to 10(15) cm, which would be unresolved at our spatial resolution. Based on the shock models of Draine and coworkers, the magnetic field strengths required to account for the Structure are in the range 10-30 muG. We suggest future high spatial resolution mapping of this feature in its near-infrared CO and H2 emission, to characterize further the temperature and density structure of the neutral gas within the shock.