Protostellar winds studied with water masers

The``Protostellar Outflows at the Earliest Stages'' (POETS) survey has recently mapped the 3D velocity field of the protostellar winds in a sample (37) of luminous young stellar objects (YSO) at scales of 10-100au via very long baseline interferometry (VLBI) observations of the 22GHz water masers. In most of the targets, the distribution of the 3D maser velocities can be explained in terms of a magnetohydrodynamic (MHD) disk-wind (DW).

We have performed multi-epoch Very Long Baseline Array (VLBA) observations of the 22GHz water masers in the YSO IRAS 21078+5211, the most promising MHD DW candidate from the POETS survey, to determine the 3D velocities of the gas flowing along several wind streamlines previously identified at a linear resolution of ~1au. By exploiting the 3D kinematic information of the masers, the launch radii of the streamlines are determined with an accuracy of ~1au and lie in the range of 10-50au.