SIMBAD references

2000MNRAS.311..329D - Mon. Not. R. Astron. Soc., 311, 329-345 (2000/January-2)

Oxygen and helium abundances in Galactic HII regions - II. Abundance gradients.


Abstract (from CDS):

The absolute integrated fluxes that we obtained (Paper I) for 34 Hii regions, with Galactocentric distances RG in the 6.6-17.7kpc range, in the emission lines [Oii] λλ3726 and 3729, [Oiii] λλ4363 and 5007, Hei λ5876, Hα and Hβ, are analysed to derive the extinctions, the electron densities and temperatures, the ionic abundances O+/H+, O++/H+ and He+/H+ and the O/H abundances.

The electron temperature has been derived from the [Oiii] λ4363/λ5007 ratio in six Hii regions with RG between 6.6 and 14.8kpc. These new measurements of Te, which are in good agreement with those from radio recombination lines, widen the RG range for which reliable Te measurements exist. Combining our new Te([Oiii]) results with the radio values, we obtain the following temperature relationship: Te K]=(372±38)RG+4260±350.

The O+/H+ and O++/H+ abundances have been obtained assuming a two-temperature Hii region model. Our O/H relationship for 5kpc<RG<15kpc is 12+logO/H= (-3.95±0.49)x10–2RG+(8.82±0.05). The slope is lower, by a factor of 2, than that previously obtained by Shaver et al. No significant flattening of this relation is obtained out to 15kpc. At the solar Galactocentric distance, 12+log(O/H)=8.48, in good agreement with the O/H abundance measured in the local interstellar medium by Meyer et al., and a factor of 2 lower than the solar abundance.

Our helium observations show that even a region ionized by a star earlier than O6.5 may contain a significant amount of neutral helium. We confirm the high ΔY/Δ(O/H) value (≥180) measured in the Galaxy by Peimbert et al.

Abstract Copyright: 2000, Royal Astronomical Society

Journal keyword(s): ISM: abundances - Hii regions - Galaxy: abundances

Simbad objects: 78

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