Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990apj...354l..57h&link_type=abstract
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 354, May 10, 1990, p. L57-L60.
Astronomy and Astrophysics
Astrophysics
18
Crab Nebula, Iron, Metallicity, Nickel, Supernova Remnants, Electron Density (Concentration), Emissivity, Forbidden Bands, Infrared Spectra, Spectrophotometry
Scientific paper
Spectrophotometric observations of the forbidden N II 1.191 micron and forbidden Fe II 1.257 micron lines at position 10 of Fesen and Kirshner in the Crab Nebula are presented. An Ni/Fe ratio of 0.3 is derived by adopting the electron temperature of 16,000 K and an electron density of 850 per cu cm. This ratio is about a factor of 6 higher than the solar ratio but is significantly smaller than the Ni/Fe ratio derived from forbidden Ni II 0.7378 micron and forbidden Fe II 0.8617 micron lines. Both of these ratios can be reconciled by increasing the electron density by a factor of approximately 10. The Ni/Fe ratio from optical lines is left unchanged, while the ratio computed from infrared lines is increased by more than a factor of 4. Since such high densities seem physically implausible, it is more likely that the atomic data for either Ni or Fe, or both, are in error, causing the infrared and optical abundance ratios to disagree.
Herter Terry
Hudgins Douglas
Joyce Richard J.
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