4.2. Structural Information
Table 6 quantifies sensitivity of the fitted parameters `a' and `b' to the (i) spectral type of embedded star, (ii) density distribution, & (iii) the optical depth. The following trends are noted. Whereas the overall angular size increases (`b' increases) as one goes from B0.5 to O7 to O4, the dependence on wavelength flattens (`a' reduces). This trend is very strong for the constant density case, irrespective of the optical depth. For the r-1 density distribution, whereas the dependence of `b' on spectral type of the star is seen clearly, the dependence of `a' becomes insensitive. However, in this case, `a' is still quite sensitive to the optical depth.
Hence, we conclude that if among the three primary details (viz., spectral type, density distribution & optical depth) of compact H II regions, any one of these is known, the other two can be reliably inferred from the spatial information.