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 _⊙ 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 μm continuum and H₂ and Brγ line emission have been performed with the Large Binocular Telescope, attaining an angular resolution of ∼90 mas and an astrometric precision of ∼100 mas. Results. While our results are consistent with previous K-band images by other authors, the improved (by a factor ∼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.