An analysis of the WN shell nebula NGC 6888 using CCD imagery and spectrophotometry

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dc.contributor.advisorDufour, Reginald J.en_US
dc.creatorMitra, Patralekhaen_US
dc.date.accessioned2009-06-04T00:43:19Zen_US
dc.date.available2009-06-04T00:43:19Zen_US
dc.date.issued1991en_US
dc.description.abstractWe present a model describing the morphology and physical processes in NGC 6888, a 'wind-blown' nebula around the WN6 star HD192163. CCD imagery with the Palomar 1.5m revealed distinct morphological features that were further probed with spectrophotometry using the KPNO #2 telescope + Intensified Reticon Scanner. Distinctions in morphology in (O III) compared to H$\alpha$ led to a parametrization into two physical systems: (1). An inner ionized shell observable in all the emission lines, with (N II) T$\sb{\rm e}$ = 8000 $\sp\circ$K, (O III) T$\sb{\rm e}$ = 14,000 $\sp\circ$K and (S II) N$\sb{\rm e}$ = 400 cm$\sp{-3.}$, (2) The (O III) bubble and rim, visible only in (O III) and characterized by a higher (O III) T$\sb{\rm e}$ = 50,000 $\sp\circ$K. The nebula is found to have 5-10 M$\sb\bigodot$ of ionized mass. An extrapolation of (O III) $\lambda$5007 fluxes to IR emission line intensities led to revised values of neutral mass $\sim$40 M$\sb\bigodot$ for the nebula. Of this 3-6 M$\sb\bigodot$ is found to be enriched mass, 0.5 M$\sb\bigodot$ contributed by stellar wind mass loss and wind swept ISM mass is determined to be $\sim$20-60 M$\sb\bigodot$. Photoionization models demonstrate that the shell is enriched in N and He and depleted in O compared to Galactic H II regions. These results collectively indicate a scenario that is a combination of several physical processes. A slow wind ejected in an asymmetric fashion from the star is swept up by a fast stellar wind together with the ambient medium, creating the ionized shell. This interaction also creates Rayleigh Taylor instabilities which are determined to be plausible formation mechanisms for the observed knots. The hot gas ($\sim$ 10$\sp7 \sp\circ$K) penetrates the nebular material in the NW and SE as there is less ejecta pressure opposing it along the polar axis, and creates the observed (O III) bubbles in the NW and lattice in the SE.en_US
dc.format.extent181 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoTHESIS SP. SCI. 1991 MITRAen_US
dc.identifier.citationMitra, Patralekha. "An analysis of the WN shell nebula NGC 6888 using CCD imagery and spectrophotometry." (1991) Diss., Rice University. <a href="https://hdl.handle.net/1911/16464">https://hdl.handle.net/1911/16464</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/16464en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjectAstronomyen_US
dc.subjectAstrophysicsen_US
dc.titleAn analysis of the WN shell nebula NGC 6888 using CCD imagery and spectrophotometryen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentSpace Scienceen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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