HD 244988

The ultraviolet spectrum of the Crab Nebula Ultraviolet spectroscopy of the Crab Nebula done by the InternationalUltraviolet Explorer satellite is described, and an estimate of thecarbon abundance is made, noting data reduction to remove spectraldefects caused by radiation hits. The important C IV 1549, He II 1640,and semiforbidden C III 1908 emission line intensities were measured andupper limits placed on other ultraviolet features for the brightestfilamentary region in the Nebula. The emission lines imply an averageionic abundance ratio n(C+2)/n(O+2) in the range from 0.4 to 1.5 in theobserved gaseous condensations. The elemental abundance ratio of carbonto oxygen is probably in the same range. Analysis shows that there is noperceptible excess of carbon due to presupernova nucleosynthesis in theobserved region. The large helium abundance, small carbon and oxygenabundances, and presence of a neutron star in the Crab Nebula suggestthat the presupernova star had a mass close to eight solar masses.
Discovery of interstellar circular polarization in the direction of the Crab nebula. Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972MNRAS.159..191M&db_key=AST
The Distribution of the BD M-Type Stars Along the Galactic Equator. Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958ApJ...128..510N&db_key=AST

SKY-MAP.ORG