A microjet: A protostar's cry at birth

We report the discovery, through Very Long Baseline Array (VLBA) observatio ns of H2O masers at 22 GHz, of a newly ejected extraordinarily compact prot ostellar jet-a microjet-from the class 0 protostar S106 LIR. The sub-AU res olution 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 assume d position of the star around the middle point of the two maser clusters. T he U-shaped distribution is considered to be a "microbowshock" created by t he impact of the microjet on the ambient cloud medium. We succeeded in trac king 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 velocitie s. In addition, this source stands unique among all 40 known class 0 source s 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 ev olutionary class, a protostar observed just after the creation of the proto stellar jet.