VLBI observations of water masers in onsala 1: Massive binary star-forming site?

We present the proper motions of water masers toward the Onsala 1 star-forming region, observed with the Japanese VLBI network at three epochs spanning 290 days. We found that there are two water-maser clusters (WMC 1 and WMC 2) separated from each other by 1 ''.6 (2900AU at a distance of 1.8kpc). A proper-motion measurement revealed that WMC I is associated with a bipolar outflow elongated in the east-west direction with an expansion velocity of 69 +/- 11 km s(-1). WMC 1 and WMC 2 are associated with two 345 GHz continuum dust emission sources, which are located 2 '' (3600 AU) east from the core of an ultracompact H 11 region traced by 8.4 GHz radio continuum emission. This indicates that the star-formation activity of Onsala 1 could move from the west side of the ultracompact H it region to the east side of two young stellar objects associated with the water masers. We have also found that the WMC 1 and UC H II regions could be gravitationally bound. Their relative velocity along the line of sight is similar to 3 km s(-1), and the total mass is similar to 37M circle dot. Onsala I seems to harbor a binary star at a different evolutionary stage.