Efficiency of the rapid neutron-capture process in the Large Magellanic Cloud

Most of the elements heavier than Fe are produced by neutron-capture processes, which can be slow or rapid (s- and r-processes). Among r-process elements, Europium is almost completely produced by this mechanism, and for this reason, its abundance in stars is commonly used as a tracer of the r-process in different environments. Recent studies have suggested that accreted stars in the Milky Way have higher [Eu/Fe] and [Eu/α] abundance ratios with respect to stars formed in situ, indicating a stronger efficiency of the r-process in the parent galaxies. For this reason, the measure of Eu abundances in Local Group galaxies such as the Magellanic Clouds is crucial to understand the assembly history of the Milky Way. The aim of this work is to compare the efficiency of production of α−elements, rapid, and slow neutron-capture elements in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). With the goal of removing any systematics that can affect different chemical analyses, we re-analysed a sample of 113 stars in the LMC (Van der Swaelmen et al., 2013) adopting the same procedures and assumptions that were used for the SMC (Anoardo et al., 2026). In both galaxies, [Mg/Fe] abundances reflect a slower star formation with respect to the Milky Way. LMC stars exhibit enhanced [Eu/Fe] values, similarly to SMC stars, indicating that the r-process is slightly enhanced with respect to the Milky Way. [Eu/Mg] is found to be compatible with the SMC and systematically higher than in Milky Way stars, proving a stronger efficiency of the r-process with respect to the α−capture process. This homogeneous comparison allows to better understand the r-process enrichment in the LMC and SMC, indicating that in environments with a lower star formation efficiency than the Milky Way, the r-process is extremely efficient and stronger than the α−capture process, and confirming that [Eu/Mg] can be a powerful tool for chemical tagging in the Milky Way.