Gas distribution at t = 10 000 yr for an enhanced mass loss with periods of 400 yr (upper panels) and 800 yr (middle panels), compared to the observed CO(2−1) line brightness distribution (lower panel). The model data have been convolved with a Gaussian of width equal to the telescope HPBW. The left panels show the distribution of the gas for velocities (V − V_∗) = ± 2 km s^-1 and the right panels the gas column density integrated over all velocities.