What produces the diffuse X-ray emission from the Orion nebula? I. Simple spherical models

The expansion of stellar wind bubbles inside evolving H ii regions is studied in spherical symmetry, with stellar wind parameters and ionizing photon rate appropriate to θ1Ori C, the main exciting source of the Orion nebula. The effects of mass loading due to embedded proplyds and thermal conduction at the edge of the hot, shocked stellar wind bubble on the expansion are investigated. The predicted X-ray luminosities and spectra of these models are calculated and compared to published observations. The models all have excess emission at higher energies compared to the observations. This emission comes from hot gas behind the stellar wind shock and its temperature depends solely on the stellar wind velocity, which for θ1Ori C is well established. Possible mechanisms for lowering the temperature of this gas are discussed.