VERA astrometry of the Galactic Superbubble NGC 281

We have used the Japanese VLBI array VERA to perform high-precision astrometry of an H 2 O maser source in the Galactic superbubble NGC 281. We successfully detected a trigonometric parallax of 0.355±0.030 mas, corresponding to a source distance of 2.82±0.24 kpc. The source distance as well as the absolute proper motions were used to demonstrate the 3D structure and expansion of the NGC 281 superbubble, ∼650 pc in size parallel to the Galactic disk, indicating the superbubble expansion may be confined to the disk. We estimate the expansion velocity of the superbubble as ∼20 km s −1 both perpendicular to and parallel to the Galactic disk with a consistent timescale of ∼20 Myr.