Annual parallax distance and secular motion of the water fountain source IRAS 18286-0959

Abstract

We report on results of astrometric observations of H2O masers in the "water fountain" source IRAS 18286-0959 (I18286) with the VLBI Exploration of Radio Astrometry (VERA). These observations yielded an annual parallax of IRAS 18286-0959, π = 0.277±0.041 mas, corresponding to a heliocentric distance of D = 3.61+0.63-0.47 kpc. The maser feature, whose annual parallax was measured, showed an absolute proper motion of (μα,μδ) = (-3.2±0.3,-7. 2±0.2) [mas yr-1]. The intrinsic motion of the maser feature in the internal motions of the cluster of features in I18286 does not seem to trace the motion of the bipolar jet of I18286. Taking into account this intrinsic motion, the derived motion of the maser feature is roughly equal to that of the maser source I18286 itself. The proximity of I18286 to the Galactic midplane (z ≈ 10 pc) suggests that the parental star of the water fountain source in I18286 should be an intermediate-mass AGB/post-AGB star, but the origin of a large deviation of the systemic source motion from that expected from the Galactic rotation curve is still unclear. © 2013 Astronomical Society of Japan.