|Speaker:||Tadafumi Matsuno (NAOJ)|
|Title:||Li Abundances in Extremely Metal-Poor Stars|
|Date:||Fri, Jun 15, 2018, 14:00 - 15:00|
|Place:||Seminar Room A|
Lithium abundances of very metal-poor stars are almost constant irrespective of metallicity (so-called Spite plateau), suggesting a direct connection to the Big Ban nucleosynthesis. However, the standard Big Bang nucleosynthesis models with cosmological parameters obtained from cosmic microwave background observations predict significantly higher primordial lithium abundance than the observed stellar lithium abundances.
A new hint to this unsolved problem could be obtained from extremely metal-poor stars ([Fe/H]<-3.0). It has been known that a portion of extremely metal-poor stars shows slightly lower lithium abundance than the Spite plateau value, which indicates that lithium depletion mechanism is at work in some stars, although it is not yet clear if there is a scatter or what governs the depletion mechanism.
To better understand the possible lithium depletion mechanism, we observe 7 extremely metal-poor stars with [Fe/H]<-3.5. As a result of chemical abundance analysis, lithium abundances of the 7 stars do not show significant scatter, but are lower than the Spite plateau. We argue that the lithium depletion mechanism is exclusively controlled by metallicity.