In the last seven years the search and analysis of extremely metal-poor (EMP) stars has witnessed an efervescent activity by various groups that adopted different successful strategies to find large numbers of EMP stars. Suffice to say that the number of stars with metallicity below -4.5 has increased almost by a factor of five since 2010. In my review I will try to capture this exceptional...
Metal-poor stars in the Milky Way is of special importance to understand the history of Galactic evolution and early nucleosynthesis. While various groups of stars showing peculiarities in kinematics and/or chemical composition are evidence of the merging process of the halo, and unusual events such as particular nucleosynthesis environments. However, these stars are rare. With its large...
The most ancient stars witnessed the assembly of the Galaxy, and they are key for studying the chemical history of the Milky Way. Extremely metal-poor stars offer an opportunity to learn about low-mass star formation, Galactic evolution and supernovae yields. During the last few years we have been exploring the SDSS and LAMOST low-resolution spectroscopic surveys to identify stars at [Fe/H]...
While theoretical simulations of Population III star formation show that protostellar disks can fragment, it is impossible for those simulations to discern if those fragments survive as low-mass stars. We report the discovery of a low-mass star on a circular orbit with orbital period $P=34.757\pm0.010$ d in the ultra metal-poor (UMP) single-lined spectroscopic binary system 2MASS...
Lithium (Li), a big-bang product that is sensitive to temperature in stellar interiors, is found to be enriched in 1$\%$ of giants in Milky Way and dwarf-spheroidals which pose challenges in low mass star's evolution. A systematic search for Li-strong stars using LAMOST spectra doubled the existing catalog of Li-rich stars, and spans super-solar metallicity to beyond [Fe/H]$\sim$-3 in...
The discovery of the 7Li abundance plateau in metal-poor dwarf stars by Spite & Spite (1982) was considered as a signature of the nucleosynthesis in the Early Universe. However, independent determination of the baryonic density from the CMB fluctuations implies a factor of 3−4 larger primordial Li abundance. More recent observations have exhibited even a lithium abundance meltdown and...
Stellar abundance measurements are heavily model dependent, and for late-type
stars, and especially for metal-poor late-type stars, the accuracy is often
limited by the use of one-dimensional (1D) hydrostatic model atmospheres and
the assumption of local thermodynamic equilibrium (LTE). Recently it has
become feasible to relax both assumptions simultaneously, i.e. to perform 3D
non-LTE...
The lowest metallicity stars that still exist today probably carry the imprint of very few supernova. As such, they represent our best observational approach to understand the First Stars. In this talk I will review the early (chemical) evolution of the Milky Way system from both modeling and observational perspectives. In particular, I will present results of the Pristine survey, a...
