Er-Tao Li

The nature of the lithium enrichment in the most Li-rich giant star

About 1% of giant stars1 have anomalously high Li abundances (ALi) in their atmospheres, conflicting directly with the prediction of standard stellar evolution models2. This finding makes the production and evolution of Li in the Universe intriguing, not only in the sense of Big Bang nucleosynthesis3,4 or the interstellar medium5, but also for the evolution of stars. Decades of effort have been put into explaining why such extreme objects exist6–8, yet the origins of Li-rich giants are still being debated. Here, we report the discovery of the most Li-rich giant known to date, with a very high ALi of 4.51. This rare phenomenon was observed coincidentally with another short-term event: the star is experiencing its luminosity bump on the red giant branch. Such a high ALi indicates that the star might be at the very beginning of its Li-rich phase, which provides a great opportunity to investigate the origin and evolution of Li in the Galaxy. A detailed nuclear simulation is presented with up-to-date reaction rates to recreate the Li enrichment process in this star. Our results provide tight constraints on both observational and theoretical points of view, suggesting that low-mass giants can internally produce Li to a very high level through 7Be transportation during the red giant phase.Star TYC 429-2097-1 contains the most lithium of any giant star, but lithium is too fragile to survive in the deep layers of a stellar atmosphere. How does the enrichment arise? Yan et al. rule out external sources (engulfment, accretion), favouring an internal process called ‘extra mixing’.

Radii of the bound states in 16 N from the asymptotic normalization coefficients

The asymptotic normalization coefficients (ANCs) of the virtual decay 16N → 15N + n are extracted from the 15N(7Li, 6Li)16N reaction populating the ground and first three excited states in 16N. The root-mean-square (rms) radii of the valence neutron in these four low-lying 16N states are then derived by using the ANCs. The probabilities of the valence neutron staying out of the core potentials are found to be 31% ± 8%, 58% ± 12%, 32% ± 8%, and 60% ± 12%. The present results support the conclusion that a one-neutron halo may be formed in the 16N first and third excited states, while the ground and second excited states do not have a one-neutron halo structure. However, the core excitation effect has a strong influence on the one-neutron halo structure of the ground and first excited states in 16N.

Experimental studies on the primordial lithium abundance

Lithium isotopes have attracted an intense interest because the abundances of both 6Li and 7Li from big bang nucleosynthesis (BBN) are the puzzles in nuclear astrophysics. Many investigations of astrophysical observation and BBN calculations have been carried out in order to solve the puzzles. Several nuclear reactions involving lithium have been determined at HI-13 tandem accelerator, Beijing, China. The BBN model calculations are then performed to investigate the primordial Lithium abundance. The result shows that these nuclear reactions have minimal effect on the primordial abundances of 6Li and 7Li.

Indirect Measurement of Astrophysical13C(α, n)16OS-Factors

The 13C(α, n)16O reaction is believed to be the main neutron source reaction for the s-process in asymptotic giant branch (AGB) stars. The astrophysical S-factors of this reaction have been determined based on an evaluation of the α spectroscopic factor of the 1/2+ subthreshold state in 17O (Ex = 6.356 MeV) by using the 13C(11B, 7Li)17O α transfer reaction. Our result confirms that the 1/2+ subthreshold resonance is dominant for the 13C(α, n)16O reaction at low energies of astrophysical interest.