Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983a%26a...120..249p&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 120, no. 2, April 1983, p. 249-262.
Astronomy and Astrophysics
Astrophysics
39
Astronomical Models, Cosmochemistry, Crab Nebula, Photoionization, Abundance, Computer Programs, Continuous Spectra, Helium, Line Spectra, Pressure
Scientific paper
Charge-exchange reactions and low temperature dielectronic combinations are taken into account in the present stationary photoionization models of a bright filament in the Crab Nebula. In a first series of models, the ionizing continuum slope is 0.5 in the UV and joins the X-ray 1.1 slope smoothly at about 0.5 keV. Constant density and constant thermal pressure models are incapable of accounting for observations. Satisfactory models which account for nearly all available lines, from UV to IR, can be obtained if the thermal pressure in the bulk of the filament is approximately twice that of the other parts. It is confirmed that the filament should resemble a cylinder rather than a sheet, since the high excitation zone must intercept a larger solid angle than the bulk of the filament. Heavy elements, as well as He, are superabundant relative to H, and an assessment of other studies indicates no heavy element abundance variations in the nebula.
Dennefeld Michel
Pequignot Daniel
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