Lithium and the early evolution of solar-type stars
by
Prof.Bengt Gustafsson(Nordita / UU)
→
Europe/Stockholm
122:026
122:026
Description
Textbooks tell us that these stars have undergone a temporary phase where
they stayed somewhere along the Hayashi line for some time and were thus
fully convective. However, they did not get hot enough in their interior to
burn lithium, and in the ensuing progress towards the main sequence the
gradually warmer radiative core developed but did not allow much of the
burnt Li-free material to the surface. This poses a problem for observed Li
in the Sun, which seems depleted by two orders of magnitude and thus must
have been mixed and burnt in the core. Instead, much of the lithium still
prevails, and new theory suggests that this textbook explanation is flawed,
Various ideas about mechanisms that have provided the extra mixing needed
are around, mainly related to the rotationally driven circulation and shear
instabilities. Gustafsson will explore another current idea, that stars
form through gradual accretion onto a core that got quite hot but was never
fully convective. He will relate the result to recent results that the
solar surface composition is affected by infall of chemically fractionated
material from the remains of the proto-planetary disk.
