In dense hot star winds, the infrared and radio continua are dominated by free‐free opacity and recombination emission line spectra. In the case of a spherically symmetric outflow that is isothermal and expanding at constant radial speed, the radiative transfer for the continuum emission from a dense wind is analytic. Even the emission profile shape for a recombination line can be derived. Key to these derivations is that the opacity scales with only the square of the density. These results are well‐known. Here an extension of the derivation is developed that also allows for line blends and the inclusion of an additional power‐law dependence beyond just the density dependence. The additional power‐law is promoted as a representation of a radius dependent clumping factor. It is shown that differences in the line widths and equivalent widths of the emission lines depend on the steepness of the clumping power‐law. Assuming relative level populations in LTE in the upper levels of He II, an illustrative application of the model to Spitzer/IRS spectral data of the carbon‐rich star WR 90 is given (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The atomic physics relevant to gaseous nebulae is critically examined using modelling software with particular emphasis on radio recombination lines (RRLs). The theoretical spectral line intensities can be deduced if we know the population structure of the bound electrons in the gas under non-thermal equilibrium conditions. The population structure of hydrogen is solved for various environments using a capture-collision-cascade model that incorporates an ambient radiation eld. The validity of assuming Case B (Baker & Menzel, 1938) for nebulae is investigated. It is known that Case B is appropriate for levels with small principal quantum numbers (n < 40), but this assumption is re-examined for high levels which are relevant to RRLs. E ects of an ambient radiation eld on the population structure is examined and processes that are stimulated by a radiation eld are included in the model. This is done as a preliminary investigation to extend the model to a photoionization code. / Physics / (M. Sc. (Astronomy)

The atomic physics relevant to gaseous nebulae is critically examined using modelling software with particular emphasis on radio recombination lines (RRLs). The theoretical spectral line intensities can be deduced if we know the population structure of the bound electrons in the gas under non-thermal equilibrium conditions. The population structure of hydrogen is solved for various environments using a capture-collision-cascade model that incorporates an ambient radiation eld. The validity of assuming Case B (Baker & Menzel, 1938) for nebulae is investigated. It is known that Case B is appropriate for levels with small principal quantum numbers (n < 40), but this assumption is re-examined for high levels which are relevant to RRLs. E ects of an ambient radiation eld on the population structure is examined and processes that are stimulated by a radiation eld are included in the model. This is done as a preliminary investigation to extend the model to a photoionization code. / Physics / (M. Sc. (Astronomy)