Application of an extended mixing length model to the convective envelope of the sun and its Li and Be content
Abstract
New solar envelope models are calculated with an improved treatment of convection. This leads to revised constraints on the depth of the (convective + underlying transport) region having to connect the surface with the region where Li and Be are destroyed in quantities required by the observations.
Our convection model, inspired by the mixing length theory, drops the assumption of incompressibility by means of the introduction of two additional free parameters.
In a first step, taking due account of dilution effects in the envelope, and assuming that no Li and Be are destroyed in the premain sequence phase, we deduce that ^{7}Li and ^{9}Be have to be mixed from the surface down to regions where the temperatures lie in the 2.6 10^{6} ≦ T ≦ 3.0 1O^{6} K and 3.6 10^{6} ≦ T ≦ 3.7 1O^{6} K ranges, respectively, the precise values of T depending on the time scale(s) of the transport mechanism(s) below the convective zone. The temperatures generally reported in the literature are lower than these (2.5 10^{6} K and 3.5 10^{6} K, respectively). We thus conclude that the transport region called for in order to explain the Li and Be observations is larger in mass than predicted up to now, except of course if the convective envelope is in its turn deeper than expected from the standard model.
In a second step, we show that the compression effects we simulate in our extended convection model may well be able to lead to a convective deepening without having to resort to any type of overshooting. Of course, this possibility has to be evaluated further by means of detailed calculations of the global evolution of the Sun.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 December 1990
 Bibcode:
 1990A&A...240..515L
 Keywords:

 Beryllium;
 Convection Currents;
 Lithium;
 Mixing Length Flow Theory;
 Solar Atmosphere;
 Stellar Composition;
 Abundance;
 Atmospheric Models;
 Nuclear Fusion;
 Solar Temperature;
 Stellar Envelopes;
 Stellar Models;
 Temperature Distribution;
 Transport Theory;
 Turbulent Diffusion;
 stars: convection;
 Sun: convection;
 Sun: abundances;
 Solar Physics