Stellar solutions for the two cosmological Li problems

ABSTRACT

In this talk I will give an overview of the history and status quo of lithium abundance determination in un-evolved stars from solar to the lowest metallicities, and their connection to Big Bang nucleosynthesis. 7Li spectroscopy now encompasses samples of hundreds of thousands of stars, largely thanks to multi-object spectrographs FLAMES/VLT and HERMES/AAT, and corresponding dedicated Galactic Archaeology surveys. The rapidly growing observational data sets has sparked development of new efficient and automated spectroscopic analysis techniques, with optimisation algorithms that also incorporate Gaia data. 6Li spectroscopy is still limited to a small, but increasing, sample of bright stars, with the best data that 8-10 m telescopes and the highest resolution instruments (HIRES/KECK, ESPRESSO/VLT) can provide. The lighter isotope, on the other hand, strongly challenges the modelling of the Li resonance line, properly accounting for the Doppler shifts induced by convective motions and the departures from LTE of the atomic level populations. I will discuss how theory and observations have developed since the discovery of the Spite plateau and argue that today, the abundance measurements of unevolved stars favour "stellar solutions" to both cosmological Li problems (i.e. for both 6Li and 7Li).