The ultraviolet spectrum of the Crab Nebula

K. Davidson, T. R. Gull, S. P. Maran, T. P. Stecher, R. A. Fesen, R. A. Parise, C. A. Harvel, M. Kafatos, V. L. Trimble
1982 Astrophysical Journal  
Data from 65 hours of observation of the Crab Nebula with the International Ultraviolet Explorer are reported, together with new ground-based spectrophotometry. We have measured the important C IV ;\1549, He II ;\1640, and C III] Xl908 emission line intensities and placed upper limits on other ultraviolet features for the brightest filamentary region in the nebula. We have also measured some ultraviolet continuum surface brightnesses at two places in the Crab. The emission lines imply an
more » ... ionic abundance ratio n(C+ 2 )jn(0+ 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. This range may be narrowed through the use of ionization calculations, but even our simple 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 8 M 0 when it was on the main sequence.
doi:10.1086/159670 fatcat:ps5vjdyyvrac5iklj6avfih7xa