This award will support a theoretical effort to explore uncertainties in nuclear reaction rates in models of nova outbursts and the structure pre-supernova stars. The principal goal will be to construct a new reaction rate library for calculations of stellar evolution. This will, for the first time, provide the ability to assign rigorous errors to the results. The calculations will explore 66 nuclear reactions on target nuclei from carbon through calcium, for which reaction rate rates are now available, as a backbone for construction of a next-generation library of thermonuclear reaction rates. The project will also employ the new reaction rate library for simulating the evolution of massive stars and classical novae.
The project will contribute to workforce development and will include the distribution of research products to the astronomical community. The input models and data and the progenitor models for studies of supernovae and novae will be made available on a website for use by advanced students and other scientists for use in their own studies. Graduate students and a postdoctoral fellow will receive training in modern experimental and theoretical techniques, lead development of a state of the art reaction rate library, use high performance computing resources, and manage large, complex data sets.
STARLIB is a next-generation, all-purpose nuclear reaction-rate library. For the first time, this library provides the rate probability density at all temperature grid points for convenient implementation in models of stellar phenomena. The recommended rate and its associated uncertainties are also included. Currently, uncertainties are absent from all other rate libraries, and, although estimates have been attempted in previous evaluations and compilations, these are generally not based on rigorous statistical definitions. A common standard for deriving uncertainties is clearly warranted. STARLIB represents a first step in addressing this deficiency by providing a tabular, up-to-date database that supplies not only the rate and its uncertainty but also its distribution. Because a majority of rates are lognormally distributed, this allows the construction of rate probability densities from the columns of STARLIB. This structure is based on a recently suggested Monte Carlo method to calculate reaction rates, where uncertainties are rigorously defined. In STARLIB, experimental rates are supplemented with theoretical rates for reactions for which no experimental input is available, and with laboratory and theoretical weak rates. STARLIB includes all types of reactions of astrophysical interest, such as (p, γ ), (p, α), (α, n), and corresponding reverse rates. Strong rates account for thermal target excitations. STARLIB will significantly improve our understanding of nuclear processes in the Universe.
