Other
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000ign..confe..32l&link_type=abstract
Ionized Gaseous Nebulae. Mexico City November 21- 24, 2000, meeting abstract
Other
2
Scientific paper
We present results from optical spectroscopic observations of planetary nebu lae (PNe) in the LMC (140), SMC (40) and NGC6822 (8). We determine light element abundances (He, C, N, O, Ne, S and Ar), in these Intermediate Mass Stars (IMS). We discussed the processed elements Helium, Carbon, Nitrogen (CNO cycle), more in detail for those objects where Carbon abundances were available, and the initial metallicities from Sulfur, Argon abundances. Oxygen can be both destroyed and produced in these stars, particularly at a low initial metallicity, the case of Neon remains still unclear. The CN or ON cycles are more effective with lower initial metallicities and are always complete for typeI nebulae. We observe an Oxygen depletion via ON reaction in the more massive progenitor stars, and an Oxygen production (like Carbon) during the 3rd dredge-up. Oxygen can therefore NOT be used to derive the Initial composition of the progenitor star: other elements like Sulfur or Argon, not affected by processing inside the Intermediate Mass Stars, have to be preferred for this purpose. We show that the 3rd dredge-up is occurring in all PNe: its efficiency too is higher with lower initial metallicities, offering an easy explanation for the higher number of carbon stars found in metal-deficient galaxies. This dredged-up carbon is sometimes transformed into Nitrogen by Hot-Bottom Burning, but in a few objects only and not even in all the more massive PNe (typeI). The results are discussed in order to better constrain the IMS evolution models, particularly the results of the 3 dredge-up and the Hot Bottom burning processes, but also in the view of their implications for the chemical evolution of these galaxies. Most of the observed effects are much more efficient in a low metallicity environment, and are not seen in our Galaxy.Consequently the observations of these nearby metal poor galaxies are necessary and important to understand the evolution of the distant and primordial galaxies.
Dennefeld Michel
François Patrick
Leisy Pierre
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