AN UPDATED⁶Li(p, α)³He REACTION RATE AT ASTROPHYSICAL ENERGIES WITH THE TROJAN HORSE METHOD

Abstract

The lithium problem influencing primordial and stellar nucleosynthesis is one of the most interesting unsolved issues in astrophysics. 6 Li is the most fragile of lithium's stable isotopes and is largely destroyed in most stars during the pre-main-sequence (PMS) phase. For these stars, the convective envelope easily reaches, at least at its bottom, the relatively low 6 Li ignition temperature. Thus, gaining an understanding of 6 Li depletion also gives hints about the extent of convective regions. For this reason, charged-particle-induced reactions in lithium have been the subject of several studies. Low-energy extrapolations of these studies provide information about both the zero-energy astrophysical S(E) factor and the electron screening potential, U e . Thanks to recent direct measurements, new estimates of the 6 Li(p, α) 3 He bare-nucleus S(E) factor and the corresponding U e value have been obtained by applying the Trojan Horse method to the 2 H( 6 Li, α 3 He)n reaction in quasi-free kinematics. The calculated reaction rate covers the temperature window 0.01 to 2T 9 and its impact on the surface lithium depletion in PMS models with different masses and metallicities has been evaluated in detail by adopting an updated version of the FRANEC evolutionary code.

ASTROPHYSICAL IMPACT OF THE UPDATED9Be(p,α)6Li AND10B(p,α)7Be REACTION RATES AS DEDUCED BY THM

“…In recent years, THM data allowed for a better understanding of different astrophysical problems, such as the study of light element burning reactions (Pizzone et al 2005(Pizzone et al , 2014Lamia et al 2008Lamia et al , 2012bLamia et al , 2012cLamia et al , 2013Tumino et al 2011aTumino et al , 2011bTumino et al , 2014Grineviciute et al 2015), CNO reactions (see La Cognata et al 2010Sergi et al 2010;Palmerini et al 2013), and removing/producing neutron reactions (Lamia et al 2008;Gulino et al 2010Gulino et al , 2013La Cognata et al 2012). …”

Lithium and boron burning S(E)-factor measurements at astrophysical energies via the Trojan Horse Method

“…These data have been used as new normalization points together with the other experimental data provided by the NACRE compilation [31]. For the 6 Li case, the THM analysis of [34] gives S(0)=3.44±0.39MeV barns and U e =355±100 eV. The THM reaction rate deviates from ∼5% to ∼15% as the temperature decreases from 1 down to 10 −2 T 9 , if compared with the evaluation of [35] (left panel of Fig.1).…”

The Trojan Horse Method as a tool for investigating astrophysically relevant fusion reactions

“…However, the comparison between the THM reaction rate and the one proposed in the widely used NACRE compilation [21] leads to a ∼20% of discrepancy, thus calling for an evaluation of the impact of the THM reaction rate in astrophysical environments. Besides the role played by deuteron, lithium-7 and lithium-6 abundances already investigated in [25][26][27][28], the THM 9 Be(p,α) 6 Li S(E)-factor measurements have been then used in [18] for evaluating the fate of 9 Be in pre-main sequence (PMS) stars by means of the PROSECCO stellar code derived from the well tested FRANEC one [22,23]. The calculations have been performed in a wide stellar mass range, starting from 0.08 M up to 0.7 M for different stellar ages and metallicity.…”