VLBI MAPS AND PROPERTIES OF THE 6 GHZ OH MASERS IN W-(OH)

We present the first maps of the (2)Pi(3/2), J = 5/2 F = 3 - 3 and F = 2 - 2 OH maser emission from W3(OH) at 6.035 and 6.031 GHz in both ri ght and left circular polarizations. We used three antennas of the Eur opean VLBI Network to achieve a spatial resolution of a few milliarcse conds (mas). Our maps, restored with a beam of 5 x 6.5 mas, show compl ex OH emission structures in several velocity channels. Weak extended emission structures could be present together with point-like sources. The minimum brightness temperature derived for individual maser spots lies in the range 0.2 - 5 10(10) K. The 6.035 GHz maser emission is c oncentrated in five distinct regions covering the western half of the compact HII region. There are significantly fewer features at 6.031 GH z although the overall spatial distributions of OH features of the F = 3 - 3 and F = 2 - 2 transitions are similar. Nearly all OH features w ith nearby center velocities and opposite senses of circular polarizat ion coincide to within one synthesized beamwidth. We identify these sp atially paired components with Zeeman pairs and derive the associated magnetic field strengths, for which some changes have been observed si nce the first experiment made by Moran et al. (1978). The field always points away from us. The strengths deduced from the 6.035 GHz data ra nge from 2 to 10 mG. At 6.031 GHz the field strengths are also less th an or equal to 10 mG with the exception of a strong feature around -42 .6 km s(-1) which gives approximate to 15 mG. This is the highest fiel d strength measured so far in an OH line. From our observations we der ived the absolute position of the maser emission to an accuracy of ord er 200 mas for both 6.035 and 6.031 GHz transitions. The fine scale al ignment of the F = 3 - 3 and F = 2 - 2 OH emission maps was made using kinematical and other physical arguments. In the richest area of indi vidual OH spots there is a good match between the strongest 6.035 and 6.031 GHz masers which thus must be excited by similar physical proces ses. However, the conditions required to excite the 6.031 GHz maser se em to be slightly different from those at 6.035 GHz because the linewi dths are narrower and the magnetic fields are stronger at 6.031 GHz.