Physical conditions of H II regions in M101 and the pregalactic helium abundance

Details Physical conditions of H II regions in M101 and the pregalactic helium abundance Physical conditions of H II regions in M101 and the pregalactic helium abundance

Oct 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apj...345..186t&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 345, Oct. 1, 1989, p. 186-195.

Astronomy and Astrophysics

Astrophysics

140

Abundance, Galactic Nuclei, H Ii Regions, Helium, Spiral Galaxies, Chemical Composition, Heavy Elements, Line Spectra, Spectrophotometry

Scientific paper

Spectrophotometry in the 3400-7400 A range is presented for eight H II regions and the nucleus of M101. The He, N, O, Ne, S, and Ar abundances relative to H are derived. The O/H ratios are smaller than previously found by about 0.2 dex. Negative gradients with galactocentric distance of the O/H, N/O, and He/H ratios are found. No gradients in the S/O, Ne/O, and Ar/O ratios are found. The pregalactic helium abundance by mass has been determined from NGC 2363, NGC 5471, and the SMC H II regions and amounts to 0.230 + or - 0.006.

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