Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...426..646r&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 426, no. 2, p. 646-652
Astronomy and Astrophysics
Astrophysics
10
Crab Nebula, Emission Spectra, Infrared Spectra, Near Infrared Radiation, Spectrum Analysis, Stellar Spectrophotometry, Supernova Remnants, Abundance, Carbon, Electron Energy, Helium, Line Spectra, Synchrotron Radiation
Scientific paper
In this paper, measurements are presented of selected near-infrared emission lines from the widely separated locations in the Crab nebula corresponding to positions 6 and 10 in the study of Fesen and Kirschner, a few line strengths are reported for position 5 as well. Among the features measured at positions 6 and 10 are (S III) lambda-9532 and (C I) lambda-9824, 9850, which were also observed in the optical study of Henry, MacAlpine, and Kirshner. By scaling both the infrared and optical data sets to these features, and including the measurements of Fesen and Kirshner as well, we tabulate relative strengths for most of the emission lines between 0.37 and 1.3 micrometers. These line ratios are used to measure the helium abundance and address abundance issues concerning carbon, nickel, and iron. Specific results are that less than 40% of the He I lambda-10830 seen from position 10 arises from collisions, indicating that the collisional contributions to the optical lines are small. For Te = 10,000 K and ne = 250/cu cm, the values which give the best fit to the optical He I lines and lambda-10830, we find N(He(+))/N(H(+)) = 0.39. With regard to carbon, the strength of (C I) lambda lambda-9824, 9850 are exceptional given the weakness of (N I) lambda lambda-5199, 10400. We discuss the possibility that the emission-line gas is carbon rich (C greater than O), and that this, in concert with irradiation by the Crab's synchrotron emission, accounts for the unusual strength of the (C I). The combined optical/IR data sets yield strengths for three lines from each of the ions Ni(+) and Fe(+). Both sets of lines are sensitive to electron temperature as well as density and should confirm whether the two ions from under identical conditions. While the answer to this question and an accurate value for the (Ni)/(Fe) ratio must await the calculation of new collisional rates for Ni(+), the electron temperature (9000 K) and density (10,000/cu cm) derived from the infrared and optical (Fe II) features differ significantly from past determinations based upon optical lines alone.
Puetter Richard C.
Rossano George S.
Rudy Richard J.
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