Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...403..673d&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 403, no. 2, p. 673-677.
Astronomy and Astrophysics
Astrophysics
21
Argon, Chemical Evolution, Galactic Evolution, Oxygen, Planetary Nebulae, Sulfur, Abundance, B Stars, Galactic Structure, H Ii Regions, Supergiant Stars, Supernovae
Scientific paper
A sample of 122 southern planetary nebulae is analyzed. The sample merges the LNA survey and that by Koeppen et al. Average oxygen, sulfur, and argon abundances are derived from different age groups of the progenitors. Sulfur and argon have increasing abundances following the metallicity. However, the oxygen abundance seems to be 0.2 dex lower than the solar value of type I planetaries, whose progenitors are not older than 1-2 Gyr. This oxygen deficiency in type I nebulae agrees with abundance determinations in H II regions, intermediate-mass supergiants, and B stars in young associations. We suggest two possible scenarios to explain these data: (1) recent infalling gas from halo, with abundance ratios similar to those expected from Type I supernovae; or (2) a relative increase in the last 5-6 Gyr of Type I supernova frequency with respect to massive type II events.
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