NORMAL AND OUTLYING POPULATIONS OF THE MILKY WAY STELLAR HALO AT [Fe/H] <–2

From detailed abundance analysis of >100 Hamburg/ESO candidate extremely metal-poor (EMP) stars we find 45 with [Fe/H] < −3.0 dex. We identify a heretofore unidentified group: Ca-deficient stars with sub-solar [Ca/Fe] ratios and the lowest neutron-capture abundances; the Ca-deficient group comprises ∼10% of the sample, excluding Carbon stars. Our radial velocity distribution shows that the carbon-enhanced stars with no s -process enhancements, CEMP-no, and which do not show C 2 bands are not preferentially binary systems. Ignoring Carbon stars, approximately 15% of our sample are strong (⩾5σ) outliers in one or more elements between Mg and Ni; this rises to ∼19% if very strong (⩾10σ) outliers for Sr and Ba are included. Examples include: HE0305−0554 with the lowest [Ba/H] known; HE1012−1540 and HE2323−0256, two (non-velocity variable) C-rich stars with very strong [Mg,Al/Fe] enhancements; and HE1226−1149, an extremely r -process rich star.