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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 tau100, 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 tau100, 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 r0, r-1 and r-2 are presented.

Figure 1a Figure 1b

Figure 1. Plots of colours as a function of optical depth tau100, for an exciting star star of type O4. The symbols box, + and triangle represent r0, r-1 and r-2 density distributions respectively. The ordinates of the plots are :- Colour using PHT-P3 and PHT-P9 filters in (a), PHT-P9 and PHT-P12 filters in (b), PHT-P12 and PHT-P13 filters in (c), PHT-P13 and PHT-P14 filters in (d), PHT-C4 and PHT-C8 filters in (e), PHT-C8 and PHT-C11 filters in (f).

Figure 2a Figure 2b
Figure 2c Figure 2d
Figure 2e

Figure 2. Plots of colours as a function of optical depth, tau100, for an exciting star of type O7. The symbols box, + and triangle represent r0, r-1 and r-2 density distributions respectively. The ordinates of the plots are :- Colour using PHT-P9 and PHT-P12 filters in (a), PHT-P12 and PHT-P13 filters in (b), PHT-P13 and PHT-P14 filters in (c), PHT-C4 and PHT-C8 filters in (d), PHT-C8 and PHT-C11 filters in (e).

Figure 3a Figure 3b
Figure 3c Figure 3d

Figure 3. Plots of colours as a function of optical depth, tau100, for an exciting star star of type B0.5. The symbols box, + and triangle represent r0, r-1 and r-2 density distributions respectively. The ordinates of the plots are :- Colour using PHT-P12 and PHT-P13 filters in (a), PHT-P13 and PHT-P14 filters in (b), PHT-C4 and PHT-C8 filters in (c), PHT-C8 and PHT-C11 filters in (d).

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 4a Figure 4b
Figure 4c Figure 4d
Figure 4e Figure 4f
Figure 4g

Figure 4. Colour-colour plots with O4 as the central star. The symbols box, + and triangle are for r0, r-1 and r-2 density distributions respectively. ``high''= higher tau100 and ``low'' = lower tau100 ends. x denote the data points from Crawford & Rowan-Robinson (1986).

Figure 5a Figure 5b
Figure 5c Figure 5d

Figure 5. Colour-colour plots with O7 as the central star. The symbols box, + and triangle are for r0, r-1 and r-2 density distributions respectively. ``high''= higher tau100 and ``low'' = lower tau100 ends. x denote the datapoint from Crawford & Rowan-Robinson (1986).

Figure 6a Figure 6b

Figure 6. Colour-colour plots with B0.5 as the central star. The symbols box, + and triangle are for r0, r-1 and r-2 density distributions respectively. ``high''= higher tau100 and ``low'' = lower tau100 ends.

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 µm, 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).

Figure 7a Figure 7b
Figure 7c

Figure 7. Plots of log of the ratio of radio flux density (F5GHz) at 5GHz to the FIR flux density (F60µm) at 60 µm as a function of the total radial optical depth (tau100). The central stars in these models are:- O4 in (a), O7 in (b) and B0.5 in (c). The symbols box and + are for r0 and r-1 density distributions respectively and the symbols Delta and x are for r-2 distribution with r* = (Rmin / 2) and with r* = (Rmin / 10) respectively.

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