A homogeneous study of the s-process in the 21mic carbon-rich post-AGB objects

TL;DR

This study analyzes the s-process element abundances in six 21-micron feature post-AGB stars using high-resolution spectra, revealing their relation to AGB nucleosynthesis and dredge-up efficiency.

Contribution

It provides a homogeneous analysis of s-process enrichment in post-AGB stars with 21-micron features, linking abundance patterns to stellar evolution models.

Findings

High s-process element overabundance confirms AGB descendants.

3rd dredge-up efficiency correlates with neutron irradiation strength.

Post-AGB stars offer valuable data for AGB nucleosynthesis models.

Abstract

We present in this paper a homogeneous photospheric abundance study, on the basis of the analysis of high resolution optical spectra, of six post-AGB objects displaying a 21mic circumstellar dust feature in their IR spectrum. The F-G spectral type of the 21mic stars make that a large range of elements including a wide variety of s-process elements, can be studied by their atomic lines. The high C/O-ratios together with the large overabundance of s-process elements prove that the objects are descendants of field carbon stars. We discuss in detail the s-process abundance distribution displayed by these 21mic stars and conclude that the 3rd dredge-up efficiency is closely related to the strength of the integrated neutron irradiation. The expected anti-correlation of the neutron irradiation with metallicity, on the other hand, contains a large intrinsic scatter. Finally we compare our results with other intrinsic and extrinsic s-process enriched objects and conclude that the post-AGB stars offer very useful complementary data to constrain the evolutionary models of AGB nucleosynthesis and dredge-up processes.