Large Magellanic Cloud Planetary Nebula Morphology: Probing Stellar Populations and Evolution

The Astrophysical Journal (Impact Factor: 6.73). 03/2000; DOI: 10.1086/312667
Source: arXiv

ABSTRACT Planetary Nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique opportunity to study both the Population and evolution of low- and intermediate-mass stars, by means of the morphological type of the nebula. Using observations from our LMC PN morphological survey, and including images available in the HST Data Archive, and published chemical abundances, we find that asymmetry in PNe is strongly correlated with a younger stellar Population, as indicated by the abundance of elements that are unaltered by stellar evolution (Ne, Ar, S). While similar results have been obtained for Galactic PNe, this is the first demonstration of the relationship for extra-galactic PNe. We also examine the relation between morphology and abundance of the products of stellar evolution. We found that asymmetric PNe have higher nitrogen and lower carbon abundances than symmetric PNe. Our two main results are broadly consistent with the predictions of stellar evolution if the progenitors of asymmetric PNe have on average larger masses than the progenitors of symmetric PNe. The results bear on the question of formation mechanisms for asymmetric PNe, specifically, that the genesis of PNe structure should relate strongly to the Population type, and by inference the mass, of the progenitor star, and less strongly on whether the central star is a member of a close binary system. Comment: The Astrophysical Journal Letters, in press 4 figures

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    ABSTRACT: A thorough critical literature survey has been carried out for reliable measurements of oxygen and neon abundances of planetary nebulae (PNe) and HII regions. By contrasting the results of PNe and of HII regions, we aim to address the issues of the evolution of oxygen and neon in the interstellar medium (ISM) and in the late evolutionary phases of low- and intermediate-mass stars (LIMS), as well as the currently hotly disputed solar Ne/O abundance ratio. Through the comparisons, we find that neon abundance and Ne/O ratio increase with increasing oxygen abundance in both types of nebulae, with positive correlation coefficients larger than 0.75. The correlations suggest different enrichment mechanisms for oxygen and neon in the ISM, in the sense that the growth of neon is delayed compared to oxygen. The differences of abundances between PNe and HII regions, are mainly attributed to the results of nucleosynthesis and dredge-up processes that occurred in the progenitor stars of PNe. We find that both these alpha-elements are significantly enriched at low metallicity (initial oxygen abundance <= 8.0) but not at metallicity higher than the SMC. The fact that Ne/O ratios measured in PNe are almost the same as those in HII regions, regardless of the metallicity, suggests a very similar production mechanism of neon and oxygen in intermediate mass stars (IMS) of low initial metallicities and in more massive stars, a conjecture that requires verification by further theoretical studies. This result also strongly suggests that both the solar neon abundance and the Ne/O ratio should be revised upwards by ~0.22 dex from the Asplund, Grevesse & Sauval values or by ~0.14 dex from the Grevesse & Sauval values. Comment: 5 pages, 2 figures, to be published in MNRAS Letter
    Monthly Notices of the Royal Astronomical Society 06/2008; · 5.52 Impact Factor
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    ABSTRACT: We present the second part of an optical spectroscopic study of planetary nebulae in the LMC and SMC. The first paper, Leisy & Dennefeld (1996), discussed the CNO cycle for those objects where C abundances were available. In this paper we concentrate more on other elemental abundances (such as O, Ne, S, Ar) and their implications for the evolution of the progenitor stars. We use a much larger sample of 183 objects, of which 65 are from our own observations, where the abundances have been re-derived in a homogeneous way. For 156 of them, the quality of data is considered to be satisfactory for further analysis. We confirm the difficulty of separating Type-I and non-type-I objects in the classical He-N/O diagram, as found in Paper I, a problem reinforced by the variety of initial compositions for the progenitor stars. We observed oxygen variations, either depletion via the ON cycle in the more massive progenitor stars, or oxygen production in other objects. Neon production also appears to be present. These enrichments are best explained by fresh material from the core or from burning shells, brought to the surface by the 3rd dredge-up, as reproduced in recent models, some including overshooting. All the effects appear stronger in the SMC, suggesting a higher efficiency in a low metallicity environment. Neither oxygen nor neon can therefore be used to derive the initial composition of the progenitor star: other elements not affected by processing such as sulfur, argon or, if observed, chlorine, have to be preferred for this purpose. Some objects with very low initial abundances are detected, but on average, the spatial distribution of PNe abundances is consistent with the history of star formation (SF) as derived from field stars in both Clouds. Comment: 22 pages, 28 figures, Accepted for publication in Astronomy & Astrophysics
    Astronomy and Astrophysics 09/2006; · 5.08 Impact Factor
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    ABSTRACT: One of the few carbon-rich environments found in interstellar space is the ejecta of asymptotic giant branch (AGB) stars. Such material, which forms a circumstellar envelope, becomes enriched in carbon due to “dredge-up” phenomena associated with nucleosynthesis. A unique organic synthesis flourishes in the gas phase in these envelopes, and radio and millimeter observations have identified a wide range of C-bearing compounds, including long acetylenic chains such as HC5N, HC7N, C4H, C6H, C8H, C6H−, C8H−, and C3O. Oxygen-rich envelopes also have a non-negligible carbon chemistry, fostering species such as HCN and HCO+. Phosphorus chemistry appears to be active as well in circumstellar shells, as evidenced by the recent detections of HCP, CCP, and PO. Radio observations also indicate that some fraction of the circumstellar molecular material survives into the planetary nebula stage, and then becomes incorporated into diffuse, and eventually, dense clouds. The complex organic molecules found in dense clouds such as Sgr B2(N) may be the products of “seed” material that can be traced back to the carbon-enriched circumstellar gas.
    Proceedings of the International Astronomical Union 01/2008; 4:147 - 156.

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