The lithium problem influencing primordial and stellar nucleosynthesis is one of the most interesting unsolved issues in astrophysics. Li-6 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 Li-6 ignition temperature. Thus, gaining an understanding of Li-6 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 Li-6(p, alpha) He-3 bare-nucleus S(E) factor and the corresponding U-e value have been obtained by applying the Trojan Horse method to the H-2(Li-6, alpha He-3) 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.
AN UPDATED 6Li(p, alpha)3He REACTION RATE AT ASTROPHYSICAL ENERGIES WITH THE TROJAN HORSE METHOD
DEGL'INNOCENTI, SCILLA;PRADA MORONI, PIER GIORGIO;
2013-01-01
Abstract
The lithium problem influencing primordial and stellar nucleosynthesis is one of the most interesting unsolved issues in astrophysics. Li-6 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 Li-6 ignition temperature. Thus, gaining an understanding of Li-6 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 Li-6(p, alpha) He-3 bare-nucleus S(E) factor and the corresponding U-e value have been obtained by applying the Trojan Horse method to the H-2(Li-6, alpha He-3) 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
