A test for asymptotic giant branch evolution theories: planetary nebulae in the Large Magellanic Cloud

Ventura, P.; Stanghellini, L.; Dell'Agli, F.; García-Hernández, D. A.; Di Criscienzo, M.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 452, Issue 4, p.3679-3688

Advertised on:
10
2015
Number of authors
5
IAC number of authors
1
Citations
28
Refereed citations
22
Description
We used a new generation of asymptotic giant branch (AGB) stellar models that include dust formation in the stellar winds to find the links between evolutionary models and the observed properties of a homogeneous sample of Large Magellanic Cloud (LMC) planetary nebulae (PNe). Comparison between the evolutionary yields of elements such as CNO and the corresponding observed chemical abundances is a powerful tool to shed light on evolutionary processes such as hot bottom burning (HBB) and third dredge-up (TDU). We found that the occurrence of HBB is needed to interpret the nitrogen-enriched (log (N/H) + 12 > 8) PNe. In particular, N-rich PNe with the lowest carbon content are nicely reproduced by AGB models of mass M ≥ 6 M⊙, whose surface chemistry reflects the pure effects of HBB. PNe with log (N/H) + 12 < 7.5 correspond to ejecta of stars that have not experienced HBB, with initial mass below ˜3 M⊙. Some of these stars show very large carbon abundances, owing to the many TDU episodes experienced. We found from our LMC PN sample that there is a threshold to the amount of carbon accumulated at AGB surfaces, log (C/H) + 12 < 9. Confirmation of this constraint would indicate that, after the C-star stage is reached, AGBs experience only a few thermal pulses, which suggests a rapid loss of the external mantle, probably owing to the effects of radiation pressure on carbonaceous dust particles present in the circumstellar envelope. The implications of these findings for AGB evolution theories and the need to extend the PN sample currently available are discussed.
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Low- to intermediate-mass (M < 8 solar masses, Ms) stars represent the majority of stars in the Cosmos. They finish their lives on the Asymptotic Giant Branch (AGB) - just before they form planetary nebulae (PNe) - where they experience complex nucleosynthetic and molecular processes. AGB stars are important contributors to the enrichment of the
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