A collimated jet and an infalling-rotating disk in G192.16-3.84 traced by H2O Maser emission

Abstract

We report on H2O masers associated with the massive-star forming region G192.16-3.84 observed with the new Japanese VLBI network at three epochs spanned for two months, which have revealed the three-dimensional kinematical structure of the whole H2O maser region in G192.16-3.84, containing two young stellar objects separated by ∼ 1200 AU. The maser spatio-kinematical structure has well persisted since previous observations, in which the masers are expected to be associated with a highly collimated bipolar jet and an infalling-rotating disk in the northern and southern clusters of H2O maser features, respectively. We estimated a jet expansion speed of ∼ 100kms-1 and re-estimated the dynamical age of the whole jet to be 5.6 × 104 yr. We investigated the spatial distribution of the Doppler velocities during the previous and present observations and the relative proper motions of H2O maser features in the southern cluster, as well as the relative bulk motion between the two maser clusters. They are well explained by a model of an infalling-rotating disk with a radius of ∼ 1000 AU and a central stellar mass of 5-10 M⊙, rather than by a model of a bipolar jet perpendicular to the observed CO outflow. Based on the derived H2O maser spatio-kinematical parameters, we discuss the formation mechanism of the massive young stellar objects and the outflow development in G192.16-3.84. © 2006. Astronomical Society of Japan.