Chemical Compositions of a sample of candidate post-AGB stars

TL;DR

This study analyzes elemental abundances in nine IRAS sources resembling post-AGB stars, revealing s-process enhancements, depletion patterns, and their relation to stellar evolution, binarity, and circumstellar environments.

Contribution

It provides the first detailed high-resolution abundance analysis for four IRAS sources and compiles a comprehensive comparison of post-AGB stars with different chemical signatures.

Findings

Detection of s-process enhancement in some IRAS sources.

Identification of depletion patterns linked to binarity and circumstellar dust.

Comparison showing s-process enriched stars are mostly single, while depleted ones are often binaries.

Abstract

We have derived elemental abundances for a sample of nine IRAS sources with colours similar to those of post-AGB stars. For IRAS 01259+6823, IRAS 05208-2035, IRAS 04535+3747 and IRAS 08187-1905 this is the first detailed abundance analysis based upon high resolution spectra. Mild indication of s-processing for IRAS 01259+6823, IRAS 05208-2035 and IRAS 08187-1905 have been found and a more comprehensive study of s-process enhanced objects IRAS 17279-1119 and IRAS 22223+4327 have been carried out. We have also made a contemporary abundance analysis of the high galactic latitude supergiants BD+39 4926 and HD 107369. The former is heavily depleted in refractories and estimated [Zn/H] of -0.7 dex most likely gives initial metallicity of the star. For HD 107369 the abundances of alpha and Fe-peak elements are similar to those of halo objects and moderate deficiency of s-process elements is seen. IRAS 07140-2321 despite being a short period binary with circumstellar shell does not exhibit selective depletion of refractory elements. We have compiled the stellar parameters and abundances for post-AGB stars with s-process enhancement, those showing significant depletion of condensable elements and those showing neither. The compilation shows that the s-process enhanced group contains very small number of binaries, and observed [alpha/Fe] are generally similar to thick disc values. It is likely that they represent AGB evolution of single stars.The compilation of depleted group contains larger fraction of binaries and generally supports the hypothesis of dusty discs surrounding binary post-AGB stars inferred via the shape of their SED and mid IR interferometry. IRAS 07140-2321 and BD+39 4926 are difficult to explain with this scenario and indicate the existence of additional parameter/condition needed to explain the depletion phenomenon.