Modelling a Circumstellar Disc Traced by Methanol Masers.

We present the accurate modelling of one methanol maser feature in NGC7538IRS1. The aim of this work is to test whether this particular maser feature traces a disc or an outflow in the immediate surroundings of a massive protostar. From our data it is clear that we are in the presence of probably the most smooth and regular maser emission discovered until now. The disc model seems to fit remarkably well the data, while a bicone jet model fails to reproduce most of the features seen in the maps and positionvelocity diagrams.