NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-19 T01:41:38 PDT
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For refcode 1989ApJ...345..186T:
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Copyright by American Astronomical Society. Reproduced by permission
1989ApJ...345..186T PHYSICAL CONDITIONS OF H II REGIONS IN M101 AND THE PREGALACTIC HELIUM ABUNDANCE S. TORRES-PEIMBERT, M. PEIMBERT, AND J. FIERRO Instituto de Astronomia, Universidad Nacional Autonoma de Mexico Received 1988 December 15; accepted 19 March 29 ABSTRACT 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. We find negative gradients with galactocentric distance of the O/H, N/O, and He/H ratios. We do not find any gradients in the S/O, Ne/O, and Ar/O ratios. 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 +/- 0.006 (1 {sigma}). Subject headings: galaxies: individual (M 101) - galaxies: nuclei - nebulae: abundances - nebulae: H II regions
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