Unveiling the disk-jet system in the massive (proto)star IRAS 20126+4104

We present the results of line and continuum observations towards the sourc e IRAS 20126+4104, performed at 1.3 mm and 3.5 mm with the Plateau de Bure interferometer, from 350 mu m to 2 mm with the James Clerk Maxwell telescop e, and at 10 and 20 mu m with the United Kingdom infrared telescope. The re sults fully confirm the findings of Cesaroni et al. (1997), namely that IRA S 20126+4104 is a very young stellar object embedded in a dense, hot core a nd lying at the centre of a rotating disk. The bipolar jet imaged by Cesaro ni et al. (1997) in the 2.122 mu m H-2 line is seen also in the SiO(2-1) tr ansition, which allows to study the velocity field in the jet. A simple mod el is developed to obtain the inclination angle of the jet (and hence of th e disk axis), which turns out to be almost perpendicular to the line of sig ht. By studying the diameter of the disk in different transitions and the c orresponding line widths and peak velocities, one can demonstrate that the disk is Keplerian and collapsing, and thus compute the mass of the central object and the accretion luminosity. We show that if all the mass inducing the Keplerian rotation is concentrated in a single star, then this cannot b e a ZAMS star, but more likely a massive protostar which derives its lumino sity from accretion.