Speaker
Description
Metal-poor stars formed in the early universe provide crucial clues to Galactic chemical evolution. Many of these stars, especially in the Milky Way halo, are enriched in carbon ([C/Fe] > 1.0) and are known as Carbon-Enhanced Metal-Poor (CEMP) stars. Based on their heavy-element enrichment patterns, they are categorized into CEMP-r, CEMP-s, and CEMP-rs subclasses, reflecting contributions from the slow (s-) and rapid (r-) neutron-capture processes. While the s-process occurs in low- to intermediate-mass AGB stars, the r-process likely occurs in neutron star mergers or certain supernovae. However, the astrophysical origin of CEMP-rs stars, enriched in both s- and r-process elements, remains uncertain. Increasing evidence suggests that the intermediate neutron-capture process (i-process), operating at neutron densities between those of the s- and r-processes, may explain this dual enrichment. In this study, we investigate the abundances of extreme r-process elements (Tb, Tm, Ir, Os, Yb, Ho, and Ta) in a sample of CEMP stars using high-resolution, high signal-to-noise near-UV spectra from UVES. Stellar parameters were derived using the BACCHUS code, and abundances were obtained through 1D LTE spectral synthesis with TURBOSPECTRUM and MARCS model atmospheres.
We also report the detection of thorium in three CEMP-rs stars, while uranium is constrained by upper limits. The observed abundance patterns, including Th, align well with i-process nucleosynthesis predictions, indicating that the i-process significantly contributes to the production of very heavy and radioactive elements in CEMP-rs stars.