Exploring the Chemical Fingerprints of Metal-Poor Stars: Insights from the MINCE III Project

The MINCE (Measuring at Intermediate Metallicity Neutron-Capture Elements) project investigates the chemical composition of stars with intermediate metallicity (-2.5 < [Fe/H] < -1.5). This third study (MINCE III) focuses on understanding neutron-capture elements, which are crucial for revealing the chemical history of the Milky Way. These elements form through processes involving neutron capture in stars and play a role in understanding early Galactic nucleosynthesis. By analyzing 99 stars with advanced observational techniques, this study enhances our knowledge of the origins of heavy elements and improves the models of Galactic chemical evolution.

Observations and Methods

Data were collected using the UVES spectrograph at the Very Large Telescope in Chile from 2020–2021. High-resolution spectra allowed the team to derive detailed chemical abundances of 32 stars from their total sample of 99. These stars span different Galactic regions, including the thin disk, thick disk, halo, and substructures such as Gaia Sausage Enceladus and Sequoia. The team used advanced computational tools to analyze the atmospheric properties and chemical compositions of these stars.

Results

The study revealed the presence of various elements, including light elements like sodium (Na) and zinc (Zn), and neutron-capture elements like strontium (Sr), barium (Ba), and europium (Eu). A particularly interesting find was a lithium-rich star (CD–28 10039), whose chemical profile defied conventional expectations. This star’s enhanced lithium levels suggest atypical processes during its evolution. Furthermore, eight stars exhibited activity markers, such as P-Cygni profiles, which highlight dynamic processes in their atmospheres.

Galactic Implications

The chemical trends observed align well with existing models of Galactic chemical evolution. The study confirmed that neutron-capture elements vary in abundance across stars, especially at lower metallicities. The abundance patterns in elements like Sr and Ba suggest their origins lie in a mix of rapid (r-process) and slow (s-process) neutron-capture events. These processes occur in phenomena like supernovae and neutron-star mergers.

Discussion

The study emphasized the importance of examining intermediate-metallicity stars, as their chemical profiles bridge gaps between metal-rich and extremely metal-poor stars. For example, trends in sulfur (S) and manganese (Mn) demonstrated how supernova contributions shift with metallicity. Additionally, the classification of stars into Galactic components revealed unique kinematic properties that inform our understanding of the Milky Way’s assembly history.

Conclusion

MINCE III significantly expands the dataset of chemical measurements in intermediate-metallicity stars. The findings validate previous studies while uncovering new details about the origins of neutron-capture elements. The results align with stochastic models of chemical evolution, supporting their use in Galactic archaeology. This work not only sheds light on the formation of heavy elements but also helps refine our understanding of the Milky Way's chemical and dynamical history.

Source: Lucertini