*4.3.1. Stellar Type O4*

A total of seven CCPs, *viz.*, [P13-14] / [P9-12], [P9-12] / [C4-8],
[P12-13] / [C4-8], [P13-14] / [C4-8], [P12-13] / [C3-9], [P13-14] / [C3-9]
and [C4-8] / [C3-9] are presented in
Figure 4.
All these CCPs very clearly distinguish the r^{-2}
density distribution law from the other two (r^{0} and r^{-1})
for the entire range of optical depth considered in the present study.
Of these, the first six
(Figures 4(a)-(f)) can also distinguish
between r^{0} and r^{-1} density distributions with very
moderate accuracies in colour determinations. The CCP [P13-14] / [P9-12]
uses wavelength bands very close to those
of IRAS mission. Hence, it is possible to compare existing
measurements of compact H II regions with the model predictions.
A sample of 27 compact H II regions selected by
Crawford &
Rowan-Robinson (1986),
has been displayed on the plot for our models
(Figure 4a).
If the exciting stars for all these were O4, then the location of the
observed points indicate
density distributions and optical depths for these
sources. Of 27, only one point falls on the r^{-2} curve and all
the rest are scattered around the line corresponding to r^{0}
dust density distribution and spanning a
_{100} range of
0.1 to 0.3. This result of predominance of uniform density distribution
is consistent with the results of
Faison et al. (1998),
Campbell et al. (1995) &
Mookerjea et al. (1999).