Precision spectroscopy to uncover the origin of the elements

Our understanding of how most elements form has improved greatly in recent decades, but key questions remain. Here we focus on two issues that will remain open into the 2040s: (i) identifying all astrophysical sources of neutron-capture elements and (ii) quantifying the output of all subclasses of type Ia supernovae (SNIa). For the first topic, we know of one confirmed r-process source: neutron star mergers (NSMs). However, they are likely not the only Galactic r-process source. Large-scale chemical abundance studies of light and heavy r-process elements are needed to clarify r-process nucleosynthesis and its astrophysical origins. For the second topic, the main progenitor of SNIa is still unknown but will likely be identified by the 2040s. What will still be lacking are observational constraints to quantify the output and relative importance of each subtype in the galactic context. A fundamental breakthrough on these questions requires abundances measured to better than 0.05 dex, which is achievable only with high signal-to-noise ratio, high-resolution spectra (R ~ 40 000). Disentangling the contribution of multiple nucleosynthesis sources requires a survey of a large number of stars, formed in a range of environments at distinct epochs. Current surveys miss crucial elements (e.g. Zn and Th) needed for these science cases, many of which are only found in blue wavelengths (380–390 nm). No precision spectroscopy survey with these characteristics is planned before the 2040s.