Synthetic AGB evolution. II. The predicted abundances of planetary nebulae in the LMC.
Abstract
In Paper 1 (Groenewegen and de Jong (1993)) of this series we presented a model to calculate in a synthetic way the evolution of asymptotic giant branch (AGB) stars. The model was applied to the Large Magellanic Cloud (LMC) and values were derived for the minimum core mass for third dredge-up, the dredge-up efficiency and the Reimers mass loss rate coefficient on the AGB. The observed carbon star luminosity function, the C/M-star ratio and the initial-final mass relation acted as constraints. In this paper we compare the predicted and observed abundances of planetary nebulae (PNe) in the LMC for the final model of Paper 1(Groenewegen and de Jong (1993)). In general there is good agreement. The discrepancy between observations and predictions in the C/O-C/N diagram suggests that either the mass loss rate of the most massive stars is underestimated or that their is no dredge-up after hot-bottom burning ceases. From the N/O-N/H diagram we deduce that on the main sequence the ratio of the oxygen abundance to the total metallicity probably was higher in the past. This is consistent with observations of the oxygen abundance in the Galaxy as well as theoretical modelling of the chemical evolution for the LMC. The location of a PN in the N/O-He/H, C/O-He/H, C/O-C/N and N/O-N/H diagrams is a good indicator of the main-sequence mass. Our model predicts the high He/H and N/O ratios observed in some planetary nebulae.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 1994
- Bibcode:
- 1994A&A...282..127G
- Keywords:
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- Abundance;
- Asymptotic Giant Branch Stars;
- Carbon Stars;
- Magellanic Clouds;
- Massive Stars;
- Planetary Nebulae;
- Stellar Composition;
- Stellar Evolution;
- Stellar Models;
- Mathematical Models;
- Stellar Luminosity;
- Stellar Mass;
- Astrophysics