Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apjs...57....1m&link_type=abstract
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 57, Jan. 1985, p. 1-62. Research supported by the Natural Science
Astronomy and Astrophysics
Astrophysics
579
Cosmochemistry, Galactic Evolution, H Ii Regions, Interstellar Gas, Nebulae, Abundance, Balmer Series, Continuous Spectra, H Beta Line, Interstellar Extinction, Nitrogen, Oxygen Spectra, Radiative Transfer, Spectral Line Width, Spectrophotometry, Sulfur
Scientific paper
The emission properties presently derived from spectrophotometric observations of 99 H II regions in 20 spiral and irregular galaxies form a one-parameter sequence, and the oxygen abundance is found to be the underlying physical determinant of the spectrum of a giant extragalactic H II region. The ionizing radiation field hardens with decreasing abundance, and oxygen and nitrogen abundances appear to be closely coupled above an oxygen abundance of about 0.2 times that of the sun. Sulfur appears to grow as a primary product of nucleosynthesis with respect to oxygen. The visual continuum of the H II regions seems to be primarily contributed by nonionizing supergiants in the embedded OB associations. The bulk of the extinction of the nebular emission is caused by surrounding dust clouds and dust uniformly distributed throughout the disk of the host galaxy.
McCall Marshall L.
Rybski Paul M.
Shields Gregory A.
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