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4.3.2. Stellar Type O7

The four CCPs for the O7 case, viz. [P13-14] / [P9-12], [P9-12] / [C4-8], [P12-13] / [C4-8] and [P13-14] / [C4-8] are displayed in Figure 5. These CCPs have been found to be sensitive enough to be used as diagnostic tools. Among these CCPs the most sensitive one is the CCP [P12-13] / [C4-8] which distinguishes all the three density distributions even if the colours are measured with a very crude accuracy of 0.5 dex in [P12-13] and 0.2 dex in [C4-8]. For the rest, it is required to achieve a colour accuracy of < 0.1 dex to draw firm conclusions about density distribution and tau100. Once again the r-2 law is the most unambiguously placed in all these CCPs. The IRAS measurements of the Crawford & Rowan-Robinson (1986) sample, have been overplotted on the CCP [P13-14] / [P9-12] (Figure 5a). With the exception of one point close to the r-2 locus, most of the points are scattered between the loci corresponding to r0 and r-1 density distributions. A comparison of this CCP for O7 (Figure 5a) with that of O4 (Figure 4a) suggests that O7 is a better description of the observations. If the distances to the individual IRAS sources would be available, then on luminosity grounds, this conclusion could be strengthened further.