Invited Speakers and Panelists

In nuclear astrophysics, a central goal is to understand the thermonuclear reactions that power stars and drive the synthesis of the chemical elements. At stellar energies, nuclear cross sections are strongly suppressed by the Coulomb barrier, making direct measurements extremely challenging. Their very low values often prevent measurements at the Earth’s surface, where cosmic-ray–induced background dominates, thus requiring uncertain extrapolations.

The Laboratory for Underground Nuclear Astrophysics (LUNA), located deep beneath the Gran Sasso mountain, was conceived to overcome these limitations. The unique underground environment drastically reduces cosmic-ray background, enabling direct measurements of key reactions at energies close to the Gamow peak for stellar scenarios. The LUNA-50kV and LUNA-400kV accelerators have provided high-precision data for several crucial reactions of hydrogen burning, while the recently installed 3.5 MV accelerator opens the way to systematic studies of helium and carbon burning processes.

Beyond its impact on stellar evolution and nucleosynthesis, LUNA also provides a unique laboratory to investigate fundamental aspects of nuclear physics at extremely low energies, with implications that extend to neutrino physics and stellar modeling The rapid progress of underground accelerators worldwide reflects the strong scientific momentum initiated by LUNA. This presentation will review the experimental techniques of underground nuclear astrophysics and the most significant results achieved so far, and will discuss the new physics opportunities currently being explored at LUNA. Particular emphasis will be given to the future perspectives offered by the LUNANOVA ERC Synergy Grant, which aims to further expand the discovery potential of underground accelerators and address open issues in nuclear astrophysics of our Sun.

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. One of the best places to search for answers is in ancient, metal-poor stars formed from the enriched gas. Their chemical makeup is a direct fingerprint of the elements produced by the stellar generations that came before them. Since the first r-process enhanced star, CS-22892-052 was discovered more than 30 years ago, multiple projects like the Hamburg/ESO R-process enhanced star survey (HERES), Chemical Evolution of R-process Elements in Stars (CERES), and the R-Process Alliance (RPA) have searched for more r-process enriched stars in the Milky Way. At the same time, numerous r-process enriched stars have been discovered in stellar streams and dwarf galaxies. This talk focuses on recent advances in finding r-process enriched metal-poor stars and what the detailed chemo-dynamical analysis of these stars can tell us about heavy element nucleosynthesis and the astrophysical site(s) of the r-process.

Abstract TBA

Core-collapse supernovae and kilonovae are together believed to produce the majority of the elements in the Universe. Their nucleosynthesis yields can be inferred in the late, nebular phases, when the ejecta become optically thin. I review how abundance analysis is carried out from such spectra using a combination of analytic methods and numeric NLTE spectral models. I discuss what we can learn about supernova progenitors and their hydrostatic nucleosynthesis from yield results for elements such as oxygen, and what can be learned about explosive nucleosynthesis from yields of elements such as nickel. The field of kilonova spectral analysis is much younger than that of supernova analysis, but moving at a very rapid speed. I comment on recent identifications of r-process elements in kilonovae, such as tellurium, and discuss the path forward to identify more elements and constrain their masses.

Abstract TBA

The astrophysical origin of heavy elements produced by neutron-capture processes remains one of the central open questions in modern astrophysics. Two main nucleosynthetic channels have been identified: the slow neutron-capture process (s-process), operating primarily in asymptotic giant branch stars and massive stars, and the rapid neutron-capture process (r-process), whose dominant astrophysical site(s) are still debated. An additional contribution from the intermediate neutron-capture process (i-process) may further shape the observed abundance patterns, particularly at low metallicity. Galactic chemical evolution (GCE) models provide a powerful framework to constrain the nature and properties of these nucleosynthetic channels by connecting stellar yields, event rates, and delay times to observed abundance trends of neutron-capture elements across different metallicities and galactic environments. In this talk, I will review both classical and recent developments in GCE modeling of neutron-capture elements. I will focus in particular on the role of the s-process in shaping neutron-capture abundances, highlighting its dependence on stellar mass and metallicity, the impact of rotation in massive stars, and the importance of adopting finely sampled grids of stellar progenitors for both massive stars and asymptotic giant branch stars. I will also discuss the treatment of r-process enrichment in GCE models, comparing the traditional approach based on prompt and delayed stellar sources with more flexible, site-independent frameworks designed to explore a broader parameter space. I will conclude by discussing the implications of these results for our understanding of heavy-element production, with particular emphasis on the frequency and delay-time distribution of neutron star mergers, the need for an early rapid r-process source, and the question of whether the r-process is universal across different astrophysical environments.

Type-I X-ray bursts are the explosive outcome of neutron stars accreting material from a binary companion star, and are the most commonly observed thermonuclear events in our night sky. The transfer of material from the companion star perturbs the neutron star and leads to distinct variations in the behaviour of the neutron star. This makes it the perfect laboratory for studying the properties of neutron stars. Understanding the burst behaviour (luminosity curve, frequency etc.) and the subsequent cooling profile of the accreted crust of the neutron star is contingent on precise knowledge of the nuclear physics which underpin these events. I will discuss the nuclear physics needs, the current state of knowledge and future measurements.

Stellar energy production has been generally well understood for more than half a century, and the hydrogen and helium fusion processes that power stars have been vigorously explored and found to be robust.  However, high resolution spectroscopy of red giant stars have found examples of light element (Li, C, N, O) abundance anomalies that appear to be difficult for ordinary stars to produce.  Here we will highlight examples of such stars in the high metallicity Galactic disk:   those with extremely low total carbon abundances; those with carbon isotopic ratios that should not exist at their surfaces; and those with impossibly large lithium abundances. These examples will demonstrate that one should not ignore annoying  nucleosynthetic exceptions in the quest to understand the broad trends in Galactic chemical evolution of light elements.

Abstract TBA

A challenge in multi-dimensional simulations is that we want to keep the reaction network as small as possible, to reduce the memory requirements and solution cost, while still accurately capturing the energy release and nucleosynthesis.  For this reason, multi-d simulations have traditionally used a small group of widely-available approximate networks.  But these hard-coded networks can be difficult to update with new nuclear data and updated rates, or to extend with new nuclei.  Furthermore, they were not written with modern computer architectures in mind, like GPUs.  The pynucastro library was created to connect nuclear data and reaction rate compilations to astrophysical simulations in a familiar python environment.  It allows for the interactive creation of custom, efficient reaction networks, making common rate approximations, like (alpha, p)(p, gamma), re-deriving reverse rates, and more, all with just a few lines of python code.  Extensive visualization tools and utilities allow for validation and pruning of networks.  These networks can then be evolved in python or exported as C++ code for use in simulation codes. In this talk, I will give an overview of pynucastro's capabilities and community-focused development model, show how we add new rates, and give examples of science applications that have used pynucastro networks.  I will also discuss future directions for the library as we near the 3.0 release milestone.