A study of the Keplerian accretion disk and precessing outflow in the massive protostar IRAS 20126+4104

We report on interferometric observations at 3.2 and 1.3 mm of the massive young stellar object IRAS 20126+4104 obtained in the (CS)-S-34 and CH3OH lines and in the continuum emission. The (CS)-S-34 data confirm the existence of a Keplerian disk, as already suggested by various authors. However, the mass of the central object is similar to 7 M-circle dot, significantly less than previous estimates. We believe that such a discrepancy is due to the fact that the rotation curve is affected not only by the star but also by the mass in the inner-most regions of the disk itself: this leads to an overestimate of the stellar mass when low-density tracers are used to study the velocity field over regions larger than a few seconds of arc (i.e. a few 0.01 pc). On the basis of the line profiles we speculate that accretion onto the star might be still occurring through the disk. This seems consistent with current models of high-mass star formation which predict an accretion luminosity equal to that of IRAS 20126+4104 for a 7 M-circle dot protostar. The CH3OH lines trace both the disk and the bipolar outflow previously detected in other molecules such as HCO+, SiO, and H-2. New H-2 images obtained at 2.2 mu m confirm that the outflow axis is undergoing precession. We elaborate a simple model that suitably fits the data thus allowing derivation of a few basic parameters of the precession.