Title: Direct Measurements of Stellar Cross Sections

Abstract: Many interesting, open questions in astrophysics ultimately touch on our understanding of stars, stellar evolution and the nuclear reactions that occur deep in the stellar interior. In many cases, the reactions of interest can be measured in the laboratory – a seemingly simple proposition because they occur at low energies and thus do not require large accelerators or intricate detector setups. However, reaction timescales can be millions to billions of years during the quiescent phases of stellar evolution, which means that cross sections are exceedingly small. This limitation can be partially overcome by using accelerators with extremely high beam currents, the approach that we have taken in constructing the dual-accelerator Laboratory for Experimental Nuclear Astrophysics (LENA). We are currently building LENA II, which will significantly extend the capabilities of the original facility.

One of the interesting questions in stellar evolution concerns the origin of abundance anomalies observed in globular clusters, which are the oldest galactic objects for which reliable ages have been determined and are thought to be the first structures to form in the early galaxy. These observations suggest a more complicated evolutionary history for globular clusters than what was previously believed. I’ll describe where we stand in our understanding of the key nuclear reactions as well as planned experiments with LENA II.

Host: Richard Longland