2000MNRAS.317..179P

We have written and tested a computer modelling program to solve line-radiative transfer in any cloud with axial symmetry using a lambda interation method. It can accept any axially symmetric velocity field, thus enabling the modelling of such objects as rotating discs, oblate or prolate spheroids, filaments and outflows. We present here a full description of the method and, by way of illustration of its use, the benefits that proposed new large millimetre telescopes would have in observing rotating circumstellar molecular discs embedded in collapsing envelopes.