High resolution CCD spectroscopy of (O II) in the bright core of the Orion Nebula
Jones, Michael R.
Doctor of Philosophy
Motion in the O$\sp+$ zone of the core of the Orion Nebula has been studied utilizing new high resolution CCD observations of the (O II) $\lambda\lambda$3726,3729 doublet. Emission associated with the main body of ionized gas inside the HII region consists of a narrow component due to direct emission and a broad reflected component globally redshifted relative to the narrow component. Line splitting blueshifted relative to the main emission has been found to the SE over an area more extensive than previously observed. We have derived the electron density from the (O II) ratio. A radial gradient peaked 45" SW of $\Theta\sp1\rm C$ Ori has been found for the main body of ionized gas. Relative to the main component the density of the split component appears to be considerably lower. The effective depth of the main emission line region is shown to be comparable to the distance between the dominate ionizing star $\Theta\sp1\rm C$ Ori and the principal ionization front. This component exhibits a radial gradient in depth centered to the SW. A rough estimate for the region emitting the split component suggests that its effective depth is comparable to that of the main region. Significant turbulent broadening exists in all components. Statistical analysis shows limited correlation over small scale sizes $\sim$10" not in accordance with the predictions of Kolmogorov theory. This discrepancy may be due to the observed curvature in the main ionization front which has not been considered in simple plane parallel models for HII region turbulence. Refinements to a recent model of Orion suggested by our data are proposed. A foreground "hinged" lid structure redirects the flow inside the nebula. The split component arises in material flowing away from an ionization front eroding the near side of the lid. Evidence that the background ionization front has an S-shaped geometry is presented. We argue that the ionization structure of the core is related to the proper motion of $\Theta\sp1\rm C$ to the SW relative to the molecular cloud.