Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983a%26a...127...42d&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 127, no. 1, Oct. 1983, p. 42-48.
Astronomy and Astrophysics
Astronomy
36
Astronomical Spectroscopy, Crab Nebula, Infrared Astronomy, Abundance, Line Spectra, Metallicity, Near Infrared Radiation, Spectrophotometry, Sulfur
Scientific paper
Near-infrared spectrophotometric data of a bright filament of the Crab Nebula are presented. Beside the expected forbidden lines of S III, they reveal a strong forbidden C I line at 9850 A and fainter lines of H3, Ar, Fe and Ni. Several weak lines are tentatively interpreted as H-alpha and forbidden S II emission from material expanding at radial velocities up to 5000 km/s. A comparison with stationary photoionization models presented in an accompanying paper shows that the lines of carbon and sulfur are explained to within a factor of 2. However, the fit is worsened when very recently available atomic-physics data are introduced. The discrepancies can be attributed either to uncompleteness of atomic-physics parameters or to simplifying assumptions of the models. A nickel-to-iron abundance ratio at least ten times the cosmic one is deduced from the observations: while the ion abundance appears to be somewhat low with respect to most other elements, possibly indicating a partial depletion into dust grains, the main problem has to be ascribed to the unexpectedly strong forbidden line of Ni II.
Dennefeld Michel
Pequignot Daniel
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