Observations of the Orion Nebula in Hα, [NII] and Hβ lines |
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| Authors: | C T Hua R Louise |
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| Institution: | 1. Laboratoire d'Astronomie Spatiale du CNRS, Marseille, France
2. Observatoire de Marseille, Marseille, France
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| Abstract: | Monochromatic photographs of the Orion Nebula taken through narrow bandpass interference filters (Δλ=10 Å) centred on Hα, Hβ and NII] lines are presented. Ratio contours of Hα/NII] and Hα/Hβ are derived. They enable a detailed study of the point-to-point variation in ionization structure and temperature throughout the nebula. Dust located within the ionized gas is studied from the Hα/Hβ ratio which varies from point to point over the nebula. Its strongest concentration, apart in the obvious ‘dark bay’, occurs in a shell surrounding the exciting stars, with about 2′ of diameter. Close to Θ1 Ori the Hα/Hβ ratio, corrected for interstellar reddening, is about 3.0 in good agreement with the predicted value (Brocklehurst, 1971). To account for these measures, the following arguments are proposed: - Dust grains are completely or partially destroyed in region close to the exciting stars.
- Radiation pressure and stellar wind push the remaining dust up to some equilibrium distance outwards. The consequence of this action is obviously the formation of a ‘dust mantle’ which is seen as a ring in projection.
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