The visual extinction in the model with OH dust and an isotropic radiation field with the intensity four times the standard value (Mathis et al. 1983). The left hand frame shows the A_V map from the model smoothed to a resolution of 18″. The right hand frame shows the A_V profile of the model (dashed line) compared to the observed profiles of (thick solid line) and (thin blue line) along the selected stripe. The latter two are the same as in Fig. 5b but are shown at their original resolution. In the plot the has been scaled by a factor of 1.3. The dotted lines are the profiles of the maximum and minimum along the stripe.