Element Settling in the Solar Interior

Abstract

Abstract.Element settling inside the Sun now becomes detectable from the comparison of the observed oscillation modes with the results of the theoretical models. This settling is due, not only to gravitation, but also to thermal di usion and radiative acceleration (although this last e ect is small compared to the two others ). It leads to abundance variations of helium and heavy elements of = 10% below the convective zone. Although not observable from spectroscopy, such v ariations lead to non-negligible modi cations of the solar internal structure and evolution. Helioseismology is a powerful tool to detect such e ects, and its positive results represent a great success for the theory of stellar evolution. Meanwhile, evidences are obtained that the element settling is slightly smoothed down, probably due to mild macroscopic motions below the convective zone. Additional observations of the abundances of both 7 Li and 3 He lead to speci c constraints on these particular motions.

Solar Elemental Abundances

“…These effects were investigated by e.g. Turcotte et al (1998), Vauclair (1998), Turcotte & Wimmer-Schweingruber, (2002) and Yang (2016Yang ( , 2019. Yang (2019) took the effects of rotation on mixing into account (see below).…”

Recent Progress and Future Prospects in Solar Physics, and Their Relevance for Planet Earth

“…Comparisons between models and helioseismic inversions have been made by, e.g., ChristensenDalsgaard et al (1996), Richard and Vauclair (1997), Turck-Chie`ze et al (2001a) or Couvidat et al (2003). Already early helioseismic results showed that the sound speed between 0.3 and 0.7 R x (below the convection zone) was higher than predicted by models, such that the assumed opacity in the models had to be re-assessed, as well as element settling and small mixing near that area (Brun et al, 1998(Brun et al, , 1999Vauclair, 1998;Turck-Chie`ze et al, 1998). A comparison of modelled and measured sound speed in the solar interior is shown in Figure 6.…”