4.3. Colour-Colour Plots (CCP)
In case the far infrared optical depth is hard
to estimate (no distance; no mass estimate from
sub-millimeter flux density etc), then
colour colour plot, CCP, is the only possible diagnostic
tool available. A CCP is the locus of colour colour point
as a function of 100, in
that plane. After studying
several combinations of the colour-colour plots, the most
promising (i.e. with maximum diagnostic power of
discriminating either the density distribution law and / or the
embedded stellar type) are presented here. As a conservative practical
criterion, only those CCPs are considered here, which
change each colour by at least 0.7 dex over the entire
100 range (0.0045 -
0.34) considered here. The number of CCPs with
good diagnostic value reduce as the stellar type changes from
O4 to O7 to B0.5.