Publication Date:
2015-09-18
Description:
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 (μ α cos , μ ) = (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: v out = 45 ± 2 km s –1 , v rot = 22 ± 3 km s –1 , i = 12° ± 2°, which are the outflow velocity, tangential rotation velocity and line-of-sight inclination, respectively. One maser feature exhibited steady acceleration which may be related to the jet rotation. During our 15-month VLBI programme there were three ‘maser burst’ events caught ‘in the act’ which were caused by the overlapping of masers along the line of sight.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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