1999A&A...345L...5M

We report simultaneous continuum (1.3cm) and H₂O maser line observations, made with the Very Large Array (A configuration), toward IRAS 18162-2048, the luminous exciting source of the HH 80-81 complex. The continuum observations, cross-calibrated with the H₂O maser emission, provide information of the thermal jet of this young massive star with unprecedented angular resolution and fidelity. We find that the jet is already collimated on scales smaller than 100AU. The analysis of the new 1.3cm data and of previously obtained 3.6cm data show that the source has the frequency dependences in major axis and flux density that characterize biconical jets. In particular, we find θ_maj∝ν^–0.7±0.1 and S_ν∝ν^0.8±0.1. An improved determination of the mass loss rate in ionized gas, {dot}(M)_ion≃9x10^–7M_☉/yr, is provided with these new observations. As it was known from previous studies, the H₂O maser emission does not coincide with the thermal jet but with a faint source of radio continuum emission displaced by ∼7" to the northeast of the thermal jet. The H₂O masers appear in two compact clusters separated by ∼20mas. One of the clusters is formed by spots in a linear geometry. The kinematics of these maser spots and their large blueshift with respect to the radial velocity of the parental molecular cloud suggest that they trace material accelerated by outflow phenomena, instead of a possible disk.