Please contact divya.singh@berkeley.edu, tianqi.zhao@berkeley.edu, or klund@berkeley.edu for zoom links.

About half the elements heavier than iron in the Universe, like silver and gold, are created in the rapid neutron-capture (r-)process. However, today almost 70 years after the theoretical prediction of this process it is still highly debated in what type of stellar explosions it can take place, and their contribution to the galactic chemical evolution. One of the best places to search for answers is in ancient, metal-poor stars. Their chemical makeup is like a time capsule, a direct fingerprint of the elements produced by the stellar generations that came before them. But two essential samples are needed: (1) a large sample of metal-poor stars to provide robust statistics on r-process enhancement and (2) a sizable sample of r-process-enhanced stars that are bright enough to allow detailed measurements of all the elements involved. That’s where the R-Process Alliance (RPA) comes in. In 2016, the RPA launched a groundbreaking survey, gathering spectra from over 2,000 stars. I will present the results of the analysis of this sample, which maps the abundances of r-process elements using the largest homogeneously analyzed sample of metal-poor stars ever assembled. With this data, the RPA is providing the first statistical dataset to answer big questions, like: How often does the r-process occur? Do multiple sites produce it? And what are the specific conditions at these stellar sites?