The chemical composition gradient across M 33

Details The chemical composition gradient across M 33 The chemical composition gradient across M 33

Dec 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988mnras.235..633v&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 235, Dec. 1, 1988, p. 633-653.

Astronomy and Astrophysics

Astronomy

231

Abundance, Chemical Evolution, Cosmochemistry, Galactic Evolution, Spiral Galaxies, H Ii Regions, Oxygen Ions, Radiation Spectra, Sulfur

Scientific paper

The abundance gradient in M 33 is studied on the basis of IPCS and CCD data on emission lines in selected H II regions, using O II, O III, S II, and S III in the wavelength range 3700-9600 A to refine the oxygen abundances in the inner parts as well as to study the behavior of S/O. Spatially resolved observations in each H II region permit the ionization structure to be studied and enable ionization parameters and stellar effective temperatures to be separately determined. The main results are: (1) the hardness of the ionizing radiation and the ionization parameter increase outwards (with diminishing abundances) along the galactic radius; (2) the O/H gradient is steep in the inner regions, but much flatter in the outer regions; (3) N/O is constant over most of the visible disk, but lower in an outer H II region; and (4) the S/H gradient is shallower than the O/H gradient exemplifying what appears to be a universal trend for S/O to decrease with O/H in H II regions. This latter trend is rather unexpected from the viewpoint of nucleosynthesis theory.

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