Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...438..170h&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 438, no. 1, p. 170-180
Astronomy and Astrophysics
Astrophysics
68
Abundance, Emission Spectra, Gradients, H Ii Regions, Line Spectra, Spiral Galaxies, Astronomical Models, Galactic Evolution, Hydrogen, Nitrogen, Oxygen, Photoionization, Stellar Temperature, Sulfur
Scientific paper
Available emission-line data have been compiled for giant H II regions located in three nearby, well-observed spirals M33, M81, and M101 in order to study the form of interstellar abundance patterns in the disks of these galaxies. Numerous line strength ratios are shown to vary systematically with galactocentric distance. Gradients for stellar effective temperature, ionization parameter, and the abundance ratios O/H, N/O, and S/O were determined using a sequential photoionization model analysis procedure. The observed behavior of line ratios across the disks of these galaxies is found to be consistent with abundance gradients which are exponential in form and have constant slopes, thereby challenging recent suggestions that gradients flatten in the outer disk. Additionally, the N/O gradient in M101 is found to be markedly steeper than in M33 and M81, suggesting that in M101 secondary nitrogen production is relatively more efficient than primary nitrogen production.
Henry Richard B. C.
Howard Joseph W.
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