Abstract
From an analysis of VLBI observations of H 2CO and OH maser emission in the direction of the ultra-conpact HII region NGC 7538-IRS 1, the following model is proposed: The HII region is surrounded by a thick dusty shell which breaks open at the two poles and there is a bipolar outflow. Around it is a rotating gas/dust ring and matter falls from the ring onto the surface of the HII region. The whole system, HII region and the ring, moves with a sight line velocity of −61.0 km/s inside a large cloud which moves with a sight line velocity of −57 km/s. The H 2CO and OH masers occur near the poles of the HII region and within 0.2 R HII of the surface. The positions of the H 2O maser and other line sources are discussed in term of this model.
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