Magnesium Isotopic Detection in Cool Stars: Tracing Nucleosynthetic Signatures from MgH Features

TL;DR

This study evaluates the reliability of MgH spectral regions for measuring magnesium isotopic ratios in cool stars, linking these ratios to nucleosynthetic processes and Galactic chemical evolution.

Contribution

It identifies the most reliable MgH spectral regions for isotopic analysis and validates a spectral synthesis pipeline across different stellar types.

Findings

Seven MgH regions are most reliable for isotopic analysis.

Strong correlation between Mg isotopes and Eu abundances, especially with $^{24}$Mg.

No significant correlation between Mg isotopes and Ba, despite shared s-process origin.

Abstract

Magnesium (Mg) isotopic ratios offer valuable insights into stellar nucleosynthesis and Galactic chemical evolution, particularly in distinguishing contributions from supernovae and asymptotic giant branch (AGB) stars. These isotopes are accessible via MgH molecular features in cool stellar atmospheres, though their measurement remains challenging across spectral types. We assess the reliability of MgH spectral regions for extracting magnesium isotopic ratios ($^{24}$Mg, $^{25}$Mg, $^{26}$Mg) in stars from M to G types and evaluate consistency with nucleosynthetic expectations. Using spectrum synthesis, we applied an analysis pipeline, validated by three well-studied reference stars, to a sample of five additional dwarf and giant stars. Individual MgH band regions were analysed for sensitivity to isotopic variation. Europium (Eu) and barium (Ba) abundances were also measured to explore correlations with Mg isotopic ratios as r- and s-process proxies. Of ten previously studied MgH wavelength regions, we identify seven as most reliable for isotopic analysis; others showed limited sensitivity across stellar types. Derived Mg isotope ratios ($^{24}$Mg, $^{25}$Mg, $^{26}$Mg) include: HD 11695-81:7:12; HD 18884-81:7:12; HD 18907-69:9:23; HD 22049-71:16:13; HD 23249-66:13:22; HD 128621-67:17:16; HD 10700-78:10:12; HD 100407-65:10:25. Comparison of Eu abundances with Mg isotopes reveals strong correlations, particularly with ($^{24}$Mg, which is predominantly produced by hydrostatic $\alpha$-capture in massive stars, a process preceding the r-process responsible for Eu. In contrast, Ba shows no significant correlation with $^{25}$Mg or $^{26}$Mg, despite their shared s-process origin. Our results demonstrate that selected MgH regions can reliably measure Mg isotopes in cool stars, providing a reproducible framework for future studies of stellar nucleosynthesis and Galactic chemical evolution.