### 3. RESULTS

**3.1. Continuum Emission From the Dust and the Gas**
The variations of the slopes of the spectral energy
distributions (SED) as a function of
_{100}, radial density
distribution law, type of exciting star etc. are quantified
as colours directly observable using the
ISOPHOT. Details about the choice of filters and their
characteristics (Table 5 in
Paper I) have been presented in
Paper I.
Figures 1, 2 and
3
represent the variation of colours
as a function of _{100},
corresponding to a central star of type
O4, O7 and B0.5 respectively. In each figure the model predictions
corresponding to dust density profiles varying as r^{0},
r^{-1} and r^{-2} are presented.

A few colour-colour plots, selected on the basis of their
diagnostic values are
presented in Figures 4,
5 and 6. While selecting
the colours, it has
been ensured that there is no filter, which is common to both
the axes, so that any correlation seen, can be regarded as genuine.

Figure 7 presents the variation
of the ratio of the predicted radio continuum
flux density at 5 GHz and the
FIR flux density at 60 *µ*m, with the optical depth.
The different curves correspond
to the different density distributions, as explained in their
captions. In this figure, there are two curves corresponding
to the r^{-2} distribution, for different assumptions about the
inner radius of the gas cloud (details in
Section 4.4).