A close-up view of a bipolar jet: Sub-arcsecond near-infrared imaging of the high-mass protostar IRAS 20126+4104

Context. The formation of OB-type stars up to (at least) 140 M-circle dot can be explained via disk-mediated accretion and in fact growing observational evidence of disk-jet systems is found in high-mass star-forming regions. Aims. With the present observations we wish to investigate at sub-arcsecond resolution the jet structure close to the well studied high-mass protostar IRAS 20126+4104, which is known to be surrounded by a Keplerian disk. Methods. Adaptive optics imaging of the 2.2 mu m continuum and H-2 and Br gamma line emission have been performed with the Large Binocular Telescope, attaining an angular resolution of similar to 90 mas and an astrometric precision of similar to 100 mas. Results. While our results are consistent with previous K-band images by other authors, the improved (by a factor similar to 3) resolution allows us to identify a number of previously unseen features, such as bow shocks spread all over the jet structure. Also, we confirm the existence of a bipolar nebulosity within 1 " from the protostar, prove that the emission from the brightest, SE lobe is mostly due to the H2 line, and resolve its structure. Conclusions. Comparison with other tracers such as masers, thermal molecular line emission, and free-free continuum emission proves that the bipolar nebulosity is indeed tracing the root of the bipolar jet powered by the deeply embedded protostar at the center of the Keplerian disk.