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

H. Van Winckel, Maarten Reyniers|arXiv (Cornell University)|Oct 6, 1999

Stellar, planetary, and galactic studies3 citations

TL;DR

This study presents a homogeneous analysis of photospheric abundances in six carbon-rich post-AGB stars with a 21 μm infrared dust feature, using high-resolution optical spectra. It finds that the strength of s-process element overabundances correlates strongly with 3rd dredge-up efficiency, while neutron irradiation shows a large intrinsic scatter with metallicity, offering key constraints on 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.

Motivation & Objective

• To investigate the s-process abundance patterns in carbon-rich post-AGB stars with a 21 μm dust feature to understand nucleosynthetic processes.
• To determine the role of the 3rd dredge-up in shaping s-process element overabundances in these evolved stars.
• To assess the relationship between neutron irradiation strength and metallicity in post-AGB stars.
• To compare results with intrinsic and extrinsic s-process objects to improve AGB evolutionary models.
• To provide a homogeneous dataset for testing nucleosynthesis and mixing processes in post-AGB evolution.

Proposed method

• High-resolution optical spectroscopy was used to measure photospheric abundances of key elements, including s-process isotopes.
• Spectral synthesis techniques were applied to derive elemental abundances from atomic lines in the stellar atmospheres.
• The analysis focused on stars with F-G spectral types, enabling detection of a wide range of s-process elements.
• Abundance patterns were compared across the six 21 μm post-AGB stars to identify trends.
• The study employed a homogeneous analysis framework to ensure consistency across all targets.
• Metallicity and C/O ratios were derived to assess their influence on s-process efficiency.

Experimental results

Research questions

• RQ1 How do s-process element abundances vary among carbon-rich post-AGB stars with a 21 μm dust feature?
• RQ2 What is the relationship between 3rd dredge-up efficiency and the strength of neutron irradiation in these stars?
• RQ3 Does the expected anti-correlation between neutron irradiation and metallicity hold with minimal scatter in these objects?
• RQ4 How do the observed abundance patterns compare to those in intrinsic and extrinsic s-process enriched stars?
• RQ5 To what extent do these post-AGB stars provide constraints on AGB nucleosynthesis and mixing models?

Key findings

• The 3rd dredge-up efficiency is strongly correlated with the strength of integrated neutron irradiation in the 21 μm post-AGB stars.
• The expected anti-correlation between neutron irradiation and metallicity exhibits a large intrinsic scatter, challenging simple models.
• High C/O ratios and strong overabundances of s-process elements confirm the stars' origin as descendants of field carbon stars.
• The s-process abundance distribution in these stars is consistent with a mixture of s-process contributions from low-mass AGB stars.
• The post-AGB phase provides complementary data to constrain AGB nucleosynthesis and dredge-up processes.
• The homogeneous analysis reveals systematic trends in s-process element overabundances that are robust across the sample.