OH maser envelopes of the "water fountain" sources

Abstract

We present results of the EVN and global VLBI observations of 1612 MHz OH masers associated with circumstellar envelopes of three "water fountain" sources, W43A, IRAS 18286−0959 and IRAS 18460−0151, which exhibit highly collimated fast stellar jets from AGB or post AGB stars. The absolute coordinates measured in accuracy of ∼10 mas, radii and velocity fields of the masers (available from W43A and IRAS 18460−0151) suggest that the host stars of the fast jets and envelopes are commonly located within a small area (<100 AU) and that the physical parameters of the envelopes are typical as seen those in Mira and OH/IR stars, except the expansion velocity in the H2O maser region (10–30 km s−1 ) slightly higher than those in Mira and OH/IR stars. We demonstrate that ignition of the stellar jet occurred within a period during which either the parental AGB envelope still keeps its intrinsic spatio-kinematical structure or it has just been transformed to an "fast equatorial flow", a sub-product of the stellar jet. Thus the OH maser properties have provided observational constraints on the evolutionary status (AGB phase is also possible) and mass of host stars (intermediate) of the water fountains.