Documentation scienceplus.abes.fr version Bêta

À propos de : Post-AGB stars in the SMC as tracers of stellar evolution: the extreme s-process enrichment of the 21  μm star J004441.04-732136.4        

AttributsValeurs
type
Is Part Of
Subject
Title
  • Post-AGB stars in the SMC as tracers of stellar evolution: the extreme s-process enrichment of the 21  μm star J004441.04-732136.4
Date
has manifestation of work
related by
Author
Abstract
  • Context. This paper is part of a larger project in which we want to focus on the still poorly understood asymptotic giant branch (AGB) third dredge-up processes and associated s-process nucleosynthesis. Aims. We confront accurate spectral abundance analyses of post-AGB stars in both the Magellanic Clouds, to state-of-the-art AGB model predictions. With this comparison we aim at improving our understanding of the 3rd dredge-up phenomena and their dependencies on initial mass and metallicity. Methods. Because of the well constrained distance with respect to Galactic post-AGB stars, we choose an extra-galactic post-AGB star for this contribution, namely the only known 21  μm object of the Small Magellanic Cloud (SMC): J004441.04-732136.4. We used optical UVES spectra to perform an accurate spectral abundance analysis. With photometric data of multiple catalogues we construct a spectral energy distribution (SED) and perform a variability analysis. The results are then compared to predictions of tailored theoretical chemical AGB evolutionary models for which we used two evolution codes. Results. Spectral abundance results reveal J004441.04-732136.4 to be one of the most s-process enriched objects found up to date, while the photospheric C/O ratio of 1.9 ± 0.7, shows the star is only modestly C-rich. J004441.04-732136.4 also displays a low [Fe/H]  =  −1.34 ± 0.32, which is significantly lower than the mean metallicity of the SMC. From the SED, a luminosity of 7600  ±  200    L⊙ is found, together with E( B −  V) = 0.64 ± 0.02. According to evolutionary post-AGB tracks, the initial mass should be  ≈1.3    M⊙. The photometric variability shows a clear period of 97.6  ±  0.3 days. The detected C/O as well as the high s-process overabundances (e.g. [Y/Fe] = 2.15, [La/Fe] = 2.84) are hard to reconcile with the predictions. The chemical models also predict a high Pb abundance, which is not compatible with the detected spectrum, and a very high 12C/ 13C, which is not yet constrained by observations. The predictions are only marginally dependent on the evolution codes used. Conclusions. By virtue of their spectral types, favourable bolometric corrections as well as their constrained distances, post-AGB stars in external galaxies offer unprecedented tests to AGB nucleosynthesis and dredge-up predictions. We focus here on one object J004441.04-732136.4, which is the only known 21  μm source of the SMC. We show that our theoretical predictions match the s-process distribution, but fail in reproducing the detected high overabundances and predict a high Pb abundance which is not detected. Additionally, there remain serious problems in explaining the observed pulsational properties of this source.
article type
publisher identifier
  • aa19150-12
Date Copyrighted
Rights
  • © ESO, 2012
Rights Holder
  • ESO
is part of this journal
is primary topic of



Alternative Linked Data Documents: ODE     Content Formats:       RDF       ODATA       Microdata