Chemical composition of post‐AGB star candidates

Abstract

We present a high-resolution detailed abundance analysis for a sample of six post-Asymptotic Giant Branch (AGB) candidate stars, five of them had not been studied spectroscopically in the optical region. All the analyzed objects are Infrared Astronomical Satellite (IRAS) sources identified as possible post-AGB on the two-color IRAS diagram. We find three objects with clear signs of evolved stars; IRAS 05338 − 3051 shows abundances similar to the RV Tauri V453 Oph; the lower-luminosity stars IRAS 18025 − 3906 are O-rich without s-process enrichment and IRAS 18386 − 1253 shows a moderate selective depletion of refractory elements generally seen in post-AGB stars (PAGBs), which show midinfrared excess; they may evolve post-Red Giant Branch (RGB) objects, in which case these would be the first Galactic counterparts of post-RGB objects observed in the Large and Small Magellanic Clouds (Kamath et al. , 2015. On the other hand, IRAS 02528 + 4350 seems to be a moderately metal-poor young object and IRAS 20259 + 4206 also seems to be a young object showing carbon deficiency; however, an analysis with better spectra might be in order to clarify its evolutionary state. Finally, our abundance calculations for the binary PAGB IRAS 17279 − 1119 are found in good agreement with those of De Smedt et al. (2016).

Optical Spectrum of Distant OH/IR Star V1648 Aql (IRAS 19386+0155)

“…3 in [47] and Figs. 5 and 6 in a recent publication [48] demonstrate, this difference can reach an order of magnitude and greater. As follows from paper [47], a great [S/Zn] ratio is typical of stars in the thick disk.…”

“…However, they have fundamentally different distributions of energy: unlike V1648 Aql, V887 Her has a double-peaked distribution typical of post-AGB stars. In the parameter domain, similar objects also located outside the Galactic plane are LN Hya [20,44,47] and the central star of the IR source IRAS 18025−3906 [48].…”