Nuclear astrophysics in the laboratory and in the universe

Abstract

Nuclear processes drive stellar evolution and so nuclear physics, stellar models and observations together allow us to describe the inner workings of stars and their life stories. This Information on nuclear reaction rates and nuclear properties are critical ingredients in addressing most questions in astrophysics and often the nuclear database is incomplete or lacking the needed precision. Direct measurements of astrophysically-interesting reactions are necessary and the experimental focus is on improving both sensitivity and precision. In the following, we review recent results and approaches taken at the Laboratory for Experimental Nuclear Astrophysics (LENA, http://research.physics.unc.edu/project/nuclearastro/Welcome.html).

Absorption and emission features of 7Be ii in the outburst spectra of V838 Her (Nova Her 1991)

“…It is worth mentioning that the depletion of oxygen and the significant enrichment in heavier elements such as sulphur and aluminium was considered as an observational evidence that breakout from the CNO cycle may have occurred in a massive ONe WD (Schatz 2004;Schwarz et al 2007;Glasner & Truran 2009). However, modeling of the outburst of V838 Her (Downen et al 2013;Champagne et al 2014) indicated a massive (1.34-1.35 M ) ONe WD, without com- Tajitsu et al (2015Tajitsu et al ( , 2016 are corrected here for the decay of 7 Be. References are: (1) Tajitsu et al (2015); (2) Molaro et al (2016), (3) Izzo et al (2018) and (4) pelling evidence for breakout (T peak in the TNR close to 3 × 10 8 K).…”

Correlated uncertainties in Monte Carlo reaction rate calculations

“…A Monte Carlo method was developed for determining statistically realistic uncertainties of reaction rates taking into account experimental uncertainties. This was then expanded by Sallaska et al (2013) and Mohr et al (2014), and summarized in Iliadis et al (2015) and Champagne et al (2014). These developments form the basis for the Starlib reaction rate library (starlib.physics.unc.edu).…”

Exploring Stars in Underground Laboratories: Challenges and Solutions

“…The combined effects of the background suppression underground and the generally improved experimental conditions (30) have led to the most accurate value to date for the E p = 70 keV resonance strength ωγ in 17 O(p,α) 14 N, namely ωγ = (10.0 ± 1.4 stat ± 0.7 syst ) neV. In turn, this has led to a factor-of-two increase in the 17 O(p,α) 14 N reaction rate and to a reduced 17 O/ 16 O ratio, with important consequences for the origin of some oxygen-rich group II presolar grains (31). Similarly, we have obtained improved results on the 18 O(p,α) 15 N cross sections and resonance strengths, with tighter constraints on oxygen isotopic ratios (29).…”

“…After all hydrogen in the core has been exhausted, the star can no longer support the weight of its outer layers, and gravitational contraction sets in once again, further heating the stellar core. Low-mass stars like the Sun will experience helium burning, producing carbon and oxygen through the fusion of 4 He nuclei (α particles) via the so-called 3α process (3α → 12 C + γ ) and the 12 C(α,γ ) 16 O reactions. Low-mass stars will eventually die as white dwarfs, i.e., highly dense and compact objects supported by electron degeneracy (5).…”

“…These may occur in the target material, or at any other point along the path of the beam. Reactions on trace contaminants in the target material (often light elements with low Coulomb barriers) can be reduced by choosing chemically pure materials for target production, by treating these materials through etching to reduce surface contaminants (15,16), or by heating the targets to drive out contaminants from their bulk (17). Similar considerations apply to other components along the beam path (e.g., apertures or collimators), which should typically be chosen to have a large atomic number (e.g., tungsten) and be frequently cleaned.…”