# The structure of the central Orion Nebula

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 Title: The structure of the central Orion Nebula Wen, Zheng O'Dell, C. Robert We have studied Hubble Space Telescope images of the Orion Nebula. Many fine scale features of the nebula and compact objects embedded in the nebula were found. Some of the compact objects were resolved or partially resolved, and exhibit comet or elongated shapes. We propose that those compact objects associated with infrared sources are protoplanetary systems. Many high ionization, high velocity bow shock structures were found in the region where the protoplanetary disk systems are concentrated. High resolution spectra of (S III) $\lambda$ 6312 A line were obtained to study the kinematic properties of the S$\sp{++}$ ions. Four velocity systems were found. Three of them were explained. The first two arise in the main and the foreground layer of the nebula, respectively. The third one results from the reflection of the first system by dust particles inside or around the nebula. An east-west velocity gradient was found for the main emission. We also studied the turbulent motion of the S$\sp{++}$ ions. The results do not agree with predictions of the available turbulence model of H II regions. High resolution (N II) $\lambda\lambda$ 6548, 6583 A, (S II) $\lambda\lambda$ 6716, 6731 A, H$\alpha$, He $\lambda$ 5876 A, and (O I) $\lambda$ 6300 A, and (S III) $\lambda$ 6312 A spectra of the nebula were obtained to study the characteristic motions of their corresponding ions. The results are consistent with those of previous detailed studies of O$\sp+$, O$\sp{++}$, and S$\sp{++}$ ions, indicating the existence of an emission from the foreground lid. Combined with results of previous emission and absorption line studies, we conclude that the line-of-sight structure of the nebula can be approximated as two emitting layers. One litter is the main body of the nebula lying at the near side of the molecular cloud OMC-1, the other is the layer at the far side of the foreground neutral lid. The gas lying in between these two layers is very tenuous. We introduced a method for modeling the geometry of the nebula. The method utilizes a density map and an H I recombination emission map of the nebula. It was applied to the main emitting layer of the nebula, which was the first attempt to quantitatively model the geometry of a nebula. The results indicate that the method is quite successful. The model geometry shows some of the features expected and improves our understanding of the prominent features observed in the nebula. Wen, Zheng. "The structure of the central Orion Nebula." Doctoral Thesis, Rice University, ETD http://hdl.handle.net/1911/16790. http://hdl.handle.net/1911/16790 1994