[Paper Review] Chemical Compositions of RV Tauri Stars and Related Objects

S. Sumangala Rao, Sunetra Giridhar|arXiv (Cornell University)|Nov 25, 2013

Stellar, planetary, and galactic studies4 references4 citations

TL;DR

This study presents a high-resolution spectroscopic abundance analysis of RV Tauri stars and related objects, revealing mild s-process enhancement in two metal-poor RVC stars—V820 Cen and IRAS 06165+3158—alongside evidence of dust-gas winnowing in SU Gem and BT Lac. The findings suggest that intrinsically metal-poor RV Tauri stars, particularly RVC types, are promising candidates for studying s-processing near the low-mass AGB end, with implications for post-AGB evolution and nucleosynthesis in low-metallicity environments.

ABSTRACT

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.

Motivation & Objective

• To investigate the chemical compositions of unexplored RV Tauri and RV Tauri-like stars to understand post-AGB evolution.
• To determine whether mild s-processing occurs in metal-poor RV Tauri stars, particularly RVC types.
• To assess the role of dust-gas winnowing in shaping abundance peculiarities in these stars.
• To identify conditions under which depletion patterns (e.g., refractory element depletion) arise, especially in binary systems.
• To clarify the connection between binarity, circumstellar material, and observed abundance anomalies in RV Tauri stars.

Proposed method

• High-resolution spectroscopy was used to derive elemental abundances from observed spectra of target stars.
• A grid of model atmospheres was employed to analyze spectral lines and determine atmospheric parameters.
• Abundance patterns were compared with interstellar medium (ISM) compositions and s-process predictions to identify nucleosynthetic signatures.
• Dust-gas winnowing was assessed by analyzing refractory-to-iron abundance ratios and comparing them with ISM-like depletions.
• Photometric and orbital data were cross-referenced with spectroscopic results to evaluate the role of binarity and circumstellar disks.
• The study compiled and re-analyzed existing abundance data on RV Tauri objects to contextualize new findings.

Experimental results

Research questions

• RQ1 Do metal-poor RV Tauri stars, particularly RVC types, exhibit measurable s-process enhancements?
• RQ2 What conditions favor dust-gas winnowing in RV Tauri stars, and how do binarity and orbital parameters influence this?
• RQ3 Why do some stars with circumstellar material and binarity (e.g., IRAS 19135+3937) show no depletion despite favorable conditions?
• RQ4 Is there a metallicity threshold below which s-processing becomes detectable in RV Tauri stars?
• RQ5 How do pulsations and mass loss affect abundance patterns in RV Tauri systems?

Key findings

• Mild s-process enhancement was detected in V820 Cen ([Fe/H] = −2.2), with s-process elements enhanced by +1.2 for lighter and +2.1 for heavier isotopes.
• IRAS 06165+3158, an RV Tauri-like object, also shows moderate s-process enhancement, though its classification remains uncertain due to lack of photometry.
• SU Gem and BT Lac exhibit clear signs of dust-gas winnowing, with refractory elements depleted relative to iron.
• IRAS 19135+3937 and IRAS 01427+4633, despite having circumstellar material and binarity, show no depletion, possibly due to short orbital periods and high mass-loss rates.
• The absence of carbon enrichment in s-process-enhanced stars like V820 Cen remains unexplained, challenging current nucleosynthesis models.
• The study confirms that RV Tauri stars in the Galactic halo, especially RVC types, are promising targets for studying s-processing at low metallicities.