Large-scale ionization fronts and the nature and distribution of light scattering particles in the Orion Nebula

Details Large-scale ionization fronts and the nature and distribution of light scattering particles in the Orion Nebula Large-scale ionization fronts and the nature and distribution of light scattering particles in the Orion Nebula

Apr 1975

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975ap%26ss..34...91d&link_type=abstract

(Symposium on Solid State Astrophysics, Cardiff, Wales, July 9-12, 1974.) Astrophysics and Space Science, vol. 34, Apr. 1975, p.

Astronomy and Astrophysics

Astrophysics

37

Astronomical Maps, Astronomical Photography, Interstellar Matter, Ionized Gases, Light Scattering, Nebulae, Astronomical Models, Density Distribution, Graphite, Ice, Image Tubes, Lyman Alpha Radiation, Optical Filters, Shock Fronts, Silicates

Scientific paper

Image-tube filter photographs calibrated against photoelectric ifiter photometry have been used to give maps of M42 in absolute flux units over the central 15 arc mm of the nebula in H~x, [N ii] ~. 6584 A), Hf3 and continuum at 24700 A. Maps of the ratios Rx/[N II] and (for the first time) of continuum/Hfl have been produced with unprecedented spatial resolution. These show that the gas to dust ratio is high near the exciting stars and falls strongly in the vicinity of large scale ionization fronts marked by minima in the Rx/[N Ii] ratio. These results are interpreted in terms of detailed shell models containing either ice or graphite or silicate scattering particles. In all models there must be a central hole in the distribution of scattering particles. The effect of neutral globules and intrusions is investigated. It is found that all types of grain are trapped inside neutral intrusions near the centre of the nebula by the pressure of the Lx light surrounding the globule, but in the early evolution of the nebula particles can escape into the ionized medium when fronts are R-type. Ice grains escaping at this time will be destroyed for distances to the exciting stars less than 1 pc. These results can explain both the central hole in dust and the underabun- dance of oxygen in the ionized gas observed earlier. Arguments depending on colour index of the scattered light indicate that mixtures of scattered light from ice in the globules and from ice in the ionized medium can explain the observations, but that the graphite and silicate particles fail. A schematic model of the Orion Nebula is presented to attempt to explain the large scale pheno- mena observed here. It demonstrates that simple shell models for this nebula are dubious

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