The R-Process Alliance: abundances of 2000 metal-poor stars

How to make gold and silver? The long-sought-after answer to this question remains one of the most challenging open problems that ties together nuclear physics with astronomy. Heavy elements like gold and silver are produced in the so-called rapid neutron-capture (r)-process. This process only occurs in rare explosive events in the Universe, like supernovae (SNe) and neutron star mergers (NSMs), making it hard for astronomers to gather direct observations of the element creation. Likewise, it is difficult for nuclear physicists to recreate and study the nuclear process in the laboratory. These obstacles are why we today, almost seven decades after the theoretical prediction of the r-process, still don’t know where in the Universe gold and silver are made. This is the question the R-Process Alliance (RPA) is trying to answer. 

The RPA is an interdisciplinary team of researchers from the astronomy and nuclear physics communities connected to IReNA with an interest in solving the big questions related to the astrophysical r-process. The first phase of the RPA work has been focused on building a stellar sample for this work. To date, the RPA has collected so-called snapshot spectra of ∼2000 stars. These stars are selected to be bright (V < 13.5), metal-poor ([Fe/H] < −2 and cold (Teff < 5500) to facilitate abundance derivation of the neutron-capture elements Strontium, Barium, and Europium, used to characterize the r-process enrichment. Analysis of this sample is now underway with an expected finish date in spring 2025. This will be the largest homogeneously analysed sample of metal-poor stars to date, and will provide the first statistical dataset to address key questions regarding the rate of the r-process, the need for multiple sites, and the characteristics of these sites.

The purpose of the proposed meeting is (1) for the r-process core and associated students to plan the next steps of the RPA ensuring the potential of this dataset is fully explored and (2) to present the results from this new, unique stellar dataset to researchers from other areas of astronomy and work together to explore this data to advance our understanding of the r-process.