A ‘water spout’ maser jet in S235AB-MIR

Abstract

We report on annual parallax and proper motion observations of H 2 O masers in S235AB-MIR, which is a massive young stellar object in the Perseus Arm. Using multi-epoch VLBI (very long baseline interferometry) astrometry we measured a parallax of = 0.63 0.03 mas, corresponding to a trigonometric distance of D = 1.56 +0.09 -0.08 kpc, and source proper motion of ( cos , ) = (0.79 0.12, -2.41 0.14) mas yr -1 . Water masers trace a jet of diameter 15 au which exhibits a definite radial velocity gradient perpendicular to its axis. 3D maser kinematics were well modelled by a rotating cylinder with physical parameters: