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  • Other Sources  (4)
  • ASTRONOMY  (4)
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  • 1
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    The ultraviolet spectrum of the Crab Nebula (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Ultraviolet spectroscopy of the Crab Nebula done by the International Ultraviolet Explorer satellite is described, and an estimate of the carbon abundance is made, noting data reduction to remove spectral defects caused by radiation hits. The important C IV 1549, He II 1640, and semiforbidden C III 1908 emission line intensities were measured and upper limits placed on other ultraviolet features for the brightest filamentary region in the Nebula. The emission lines imply an average ionic abundance ratio n(C+2)/n(O+2) in the range from 0.4 to 1.5 in the observed gaseous condensations. The elemental abundance ratio of carbon to oxygen is probably in the same range. Analysis shows that there is no perceptible excess of carbon due to presupernova nucleosynthesis in the observed region. The large helium abundance, small carbon and oxygen abundances, and presence of a neutron star in the Crab Nebula suggest that the presupernova star had a mass close to eight solar masses.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 253
    Format: text
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  • 2
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    The Crab Nebula. I - Spectrophotometry of the filaments (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Relative line intensities in the 3700-7400 A region are obtained from new spectrophotometric measurements of ten positions in the Crab Nebula. O III forbidden line intensities imply electron temperatures of 11,000-18,300 K, while generally lower temperatures are indicated by the O II, N II and S II forbidden lines. The 6717 and 6731 A forbidden S II line ratio yields electron density estimates of 550-3500/cu cm, with a typical filament value of 1300 cu cm. While Balmer decrements are generally consistent with pure recombination, some filaments show steeper decrements. He line intensities are found to have significant variation. The presence of a moderately strong line at 7378 A, which may be due to the Ni II forbidden line is confirmed. Some filaments are found to exhibit a wide range of ionization states.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 258
    Format: text
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  • 3
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    Optical spectrophotometry of the Cygnus Loop (1982)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: Cygnus Loop filament optical spectral properties are discussed, with emphasis on comparisons between observational and model data. Some line intensities are correlated among filaments in such a way as to suggest that a well resolved ionization structure behind the shock front is being observed. Departures from the steady flow condition assumed in the present model are found to be necessary in order to improve agreement with observations.
    Keywords: ASTRONOMY
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  • 4
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    An optical investigation of the peculiar supernova remnant CTB 80 (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Interference-filter photographs and optical spectrophotometry are used to investigate the optical emission associated with the peculiar supernova remnant CTB 80. Optically, the remnant consists of outlying diffuse and filamentary emission surrounding a small, central ring of filaments which are coincident with the central radio emission peak. Spectra of two filaments in the southwestern part of the remnant show strong forbidden S II emission relative to H-alpha; in conjunction with the nonthermal radio emission in this region, this suggests that the filaments are shock heated. Filaments outside the radio structure in the northeast show a similar optical spectrum and may also be a part of CTB 80. The central filaments form a well-defined shell structure in the light of forbidden O III emission 5007 A but are irregular in H-alpha showing both knots and diffuse emission.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 282; 161-163
    Format: text
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