SIMBAD references

We present measurements of the distribution of the OH masers at 1665 and 1667MHz towards the cometary ultracompact Hii region in the complex G34.3+0.2. The results are based on observations made in both senses of circular polarization with a very long baseline interferometry (VLBI) array having an angular resolution of 5x20mas². 38 maser features are identified in the region. 33 of these lie on an arc at the edge of the cometary Hii region. Five are located in a cluster offset toward the north-east by 3arcsec, and are probably associated with an independent ultracompact Hii region. There is a velocity gradient of 30km.s^–1.pc^–1 across the arc. We identify five Zeeman pairs and determine that the magnetic field varies between 1 and 7mG, but is always directed away from the Earth.

The OH masers may arise in clumps in a shell of gas in a bow shock caused by the motion of the exciting star through the molecular cloud. The stand-off distance and the thickness of the shocked shell are roughly consistent with those predicted by such a bow-shock model. Also, the position of the exciting star(s), as estimated from the focus of the parabolic bow shock, closely matches that of the peak emission from the cometary Hii region. However, the north-south velocity gradient in the ionized material remains difficult to explain in the context of the bow-shock model.