Abstract
Interferometric maser observations of several molecular species (e.g., H[2]O, OH, CH[3]OH) provide a very powerful tool to study with high-angular resolution the molecular gas close to protostars. In this way, groups of maser spots have been found to be associated with radio-continuum jet sources in young stellar objects. In some cases, masers seem to be distributed in a band perpendicular to the central radio-continuum jet as might be expected for accretion disks. In other cases, the masers seem to be distributed along the jet source, consistent with being part of the outflow. Recently, a new way to study these star-forming regions through Very Long Baseline Interferometry (VLBI) measurements of the proper motions of the associated masers has emerged. These observations provide angular resolutions up to a few tenths of a milliarcsecond (a few tenths of an astronomical unit at a distance of 500 pc). Here we review some of these studies.
