Lifting the Veil on Ultra Metal-Poor Stars in the Outermost Halo

Abstract

The study of extremely metal-poor (EMP; [Fe/H] < −3.0) and ultra metal-poor (UMP; [Fe/H] < −4.0) stars is crucial for better understanding first-star nucleosynthesis and constraining the initial mass function in the early Universe. However, UMP stars discovered in the past 25 years only number ∼25. A few recent theoretical studies have pointed out that there is likely to exist large numbers of EMP and UMP stars in the periphery of the Galactic halo, at distances exceeding 30-50 kpc. We present identifications …