Very Large Array Simultaneous 1.3 cm Continuum and H2O Maser Observations toward IRAS 20126+4104

[[abstract]]We have observed simultaneously the 1.3 cm continuum and H2O maser emission toward the high-mass protostar IRAS 20126+4104 with the Very Large Array (VLA) in its A configuration, providing an angular resolution of 01. We have detected an unresolved continuum source [I20126N(1.3 cm)] nearly coinciding with the strongest peak of the northern double continuum source previously detected at 3.6 cm in the field and suggested to be a radio jet. In addition, we have detected 29 water maser spots, 21 of which are tightly grouped in a cluster of 01 size displaced 007 (120 AU) northwest of I20126N(1.3 cm). The relative positions of the masers with respect to I20126N(1.3 cm) have been established with 10 mas of accuracy. The overall spatial distribution and line-of-sight velocity components of the water maser spots associated with I20126N(1.3 cm) are fully consistent with those previously found by Moscadelli and collaborators through VLBI measurements and interpreted as tracing a conical outflow, with the powering source (suggested to be traced by a one-sided radio continuum jet) located at the cone vertex. Within this very reasonable scenario, our observations would indicate that the source I20126N(1.3 cm) is showing the position of the high-mass protostar. Analyzing the spatiokinematic distribution of the VLA water masers, we propose that their motions also show, in addition to proper motions on the order of 100 km s-1 seen in the plane of the sky, a component of rotation with velocities on the order of 20 km s-1. The water masers seem then to be both rotating (as evidenced from their radial velocities) and changing their position in the plane of the sky (from the proper motions). Within this scenario, some of the water maser spots could be within a rotating circumstellar disk of 170 AU size around a protostar of 20 M if it is located at the center of the water maser cluster rather than located at the position of I20126N(1.3 cm). Then, I20126N(1.3 cm) would trace one of the two peaks of a two-sided thermal jet, with the high-mass protostar located in between. We think that simultaneous high angular resolution and sensitive multifrequency (from centimeter to submillimeter wavelengths) observations are the key studies to knowing both the nature of the continuum emission (one- or two-sided jet?) and the location of the high-mass protostar, which is very relevant for modeling this important object.[[fileno]]2010504010038[[department]]天文