1995A&AS..112..299T

We present A-configuration VLA observations of the 22GHz H₂O maser line and 8.4GHz continuum emission of 22 selected CO bipolar outflows associated with water masers. These observations allow us to study the region within 10⁴AU of the engine powering the outflow. The positions of the maser spots are compared with those of ultra-compact (UC) continuum sources found in our observations, with IRAS data and with data from the literature on the molecular outflows. Weak unresolved continuum sources are found in several cases associated with the maser. Most probably they represent the ionized envelope surrounding the young stellar object (YSO) which powers the maser and the outflow. These weak radio continuum sources are not necessarily associated with the IRAS sources, which are more representative of the global emission from the star forming region. A comparison of the velocity pattern of the CO outflow with those of the maser spots detected with the VLA is also made. Asymmetries in the H₂O velocities are found on opposite sides of the YSO, suggesting that the outflow acceleration begins from the YSO itself. In a few cases we find evidence for two outflows in different evolutionary stages. The H₂O masers in these sources are always found at the centre of the younger outflow. The degree of variability of each maser is derived from single dish observations obtained with the Medicina radiotelescope before and after the VLA observations. Velocity drifts of some features are interpreted as acceleration of the maser.