Mathematics – Logic
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994mnras.266..421h&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. 266, NO. 2/JAN15, P. 421, 1994
Mathematics
Logic
26
Scientific paper
We present new long-slit spectrophotometric measurements of 10 giant H II regions located in the Virgo spiral NGC 4254. Gradients in the emission-line ratios log R_23_, log [N II]/[O II] and log [S II]/[O II] are observed and provide the constraints for a photoionization analysis to determine disc abundance patterns for O/H, N/H and S/H. We find that log O/H+ 12 = 9.52(+/-0.1)-0.27(+/-0.005)ρ/ρ_eff_; log N/H= 8.62(+/-0.1)-0.38(+/-0,05)ρ/ρ_eff_; and log S/H=7.70(+/-0.1)- 0.27(+/-0.005){rho/ρ_eff_. Adopting a distance of 18 Mpc to NGC 4254, the slopes become -0.06, - 0.08 and - 0.06 dex kpc^-1^ respectively. The value of log O/H at the nucleus indicates that the disc of NGC 4254 has a very high metallicity relative to other spirals in its morphological class. We observe a rapid rise in metallicity as the gas fraction decreases near the nucleus, perhaps providing evidence for metallicity- sensitive nucleosynthesis. In addition, our models indicate that the stellar effective temperature and the log of the ionization parameter are constant across the disc at 35 500+/-3000 K and -2.9+/-0.3, respectively. Combination of information on gas distribution with our abundance results suggests that the O and S abundance patterns are best described by a simple model of chemical evolution with relatively constant yields near the solar mass fractions for these elements. The results for N imply some secondary contribution to its build-up.
Chincarini Guido L.
Henry Richard B. C.
Pagel Bernard E. J.
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