A microjet: A protostar's cry at birth

We report the discovery, through Very Long Baseline Array (VLBA) observations of H2O masers at 22 GHz, of a newly ejected extraordinarily compact protostellar jet-a microjet-from the class 0 protostar S106 LIR. The sub-AU resolution VLBA observations revealed the presence of a U-shaped distribution of the masers in the western blue;shifted cluster. It has a length of 4 AU, has a width of 3 AU, and is located at a distance of 25 AU from the assumed position of the star around the middle point of the two maser clusters. The U-shaped distribution is considered to be a microbowshock created by the impact of the microjet on the ambient cloud medium. We succeeded in tracking the proper motion of the microbowshock; its velocity ranges from 25 to 45 km s(-1), estimated from the proper motions and line-of-sight velocities. In addition, this source stands unique among all 40 known class 0 sources in its lack of an extensive molecular outflow, evidenced by our sensitive multitransition CO searches with 10 sigma upper limits of similar to 10(-6) M-. km(-1) s. We propose that S106 FIR is an archetype of the youngest evolutionary class, a protostar observed just after the creation of the protostellar jet.