We have derived elemental abundances for a sample of nine IRAS sources with colours similar to those of post-asymptotic giant branch (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 has been found and a more comprehensive study of s-process-enhanced objects IRAS 17279−1119 and IRAS 22223+4327 has 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 α 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 a 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 a very small number of binaries, and observed [α/Fe] are generally similar to thick-disc values. It is likely that they represent AGB evolution of single stars.The compilation of the depleted group contains a larger fraction of binaries and generally supports the hypothesis of dusty discs surrounding binary post-AGB stars inferred via the shape of their spectral energy distribution and mid-infrared interferometry. IRAS 07140−2321 and BD+39• 4926 are difficult to explain with this scenario and indicate the existence of an additional parameter/condition needed to explain the depletion phenomenon. However, the conditions for discernible depletion, minimum temperature of 5000 K and initial metallicity larger than −1.0 dex found from our earlier work still serve as useful criteria.

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We have conducted an LTE abundance analysis for SAO 40039, a warm post-AGB star whose spectrum is known to show surprisingly strong He i lines for its effective temperature and has been suspected of being H-deficient and He-rich. High-resolution optical spectra are analyzed using a family of model atmospheres with different He/H ratios. Atmospheric parameters are estimated from the ionization equilibrium set by neutral and singly ionized species of Fe and Mg, the excitation of Fe i and Fe ii lines, and the wings of the Paschen lines. On the assumption that the He i lines are of photospheric and not chromospheric origin, a He/H ratio of approximately unity is found by imposing the condition that the adopted He/H ratio of the model atmosphere must equal the ratio derived from the observed He i triplet lines at 5876, 4471 and 4713Å, and singlet lines at 4922 and 5015Å. Using the model with the best-fitting atmospheric parameters for this He/H ratio, SAO 40039 is confirmed to exhibit mild dust-gas depletion, i.e., the star has an atmosphere deficient in elements of high condensation temperature. The star appears to be moderately metal-deficient with [Fe/H]=−0.4 dex. But the star's intrinsic metallicty as estimated from Na, S and Zn, elements of a low condensation temperature, is [Fe/H] o 1 =≃ −0.2. The star is enriched in N and perhaps O too, changes reflecting the star's AGB past and the event that led to He enrichment.

We have undertaken a comprehensive abundance analysis for a sample of relatively unexplored RV Tauri and RV Tauri like stars to further our understanding of post-Asymptotic Giant Branch (post-AGB) evolution. From our study based on high resolution spectra and grid of model atmospheres, we find indications of mild s-processing for V820 Cen and IRAS 06165+3158. On the other hand, SU Gem and BT Lac exhibit the effects of mild dust-gas winnowing. We have also compiled the existing abundance data on RV Tauri objects and find that a large fraction of them are afflicted by dust-gas winnowing and now added by the present work, we find a small group of two RV Tauris showing mild s-process enhancement in our Galaxy. With two out of three reported s-process enhanced objects belonging to RV Tauri spectroscopic class C, these intrinsically metal-poor objects appear to be promising candidates to analyse the possible s-processing in RV Tauri stars.

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