Speaker
Description
The rapid neutron-capture process (r-process) is responsible for producing roughly half of the elements heavier than iron, including Ag, Au, Th, and U. Despite its fundamental role in cosmic chemical evolution, the astrophysical sites and physical conditions of the r-process remain poorly constrained. Metal-poor, r-process enhanced stars provide unique laboratories to address this problem, as their surface abundances preserve the chemical signature of the gas from which they formed. However, extracting precise and reliable abundance patterns from high-resolution spectra critically depends on the accuracy of the underlying atmospheric models and spectral analysis techniques.
In this contribution, I present a new high-precision abundance analysis of the very metal-poor ([Fe/H]~-3.5) and r-process enhanced star SMSS J200322.54−114203.3, previously studied in 1D LTE by Yong et al. (2021). Our analysis is based on high-resolution UVES spectroscopy, combined with state-of-the-art 3D hydrodynamical model atmospheres and (non-)local thermodynamic equilibrium (NLTE/LTE) radiative transfer. We derive full 3D NLTE abundances for Na, Mg, Al, Si, Ca, Cu, Ag, and Ba, and 3D LTE abundances for additional neutron-capture elements. This homogeneous approach allows us to directly quantify the systematic biases introduced by commonly adopted 1D LTE methods.
Our preliminary results reveal large and element-dependent discrepancies with respect to previous 1D LTE studies, with 3D NLTE corrections reaching up to ~1 dex for some key elements, most notably aluminium and magnesium. These differences propagate into the elemental ratios that are widely used to compare observed stars with theoretical nucleosynthetic yields. In particular, the 1D LTE abundances reported by Yong et al. were found to correlate well with magnetorotational hypernova yield models. Our revised 3D (NLTE/LTE) abundance pattern substantially alters several of these key ratios and therefore challenges this apparent agreement, with important consequences for identifying the physical site of the r-process event and for tracing its contribution to the early chemical evolution of the Milky Way.