Outliers in the 0Z Survey

Abstract

We have now completed detailed abundance analyses of more than 100 stars selected as candidate extremely metal-poor stars with [Fe/H] < –3.0 dex. Of these 18 are below –3.3 dex on the scale of the First Stars VLT project led by Cayrel, and 57 are below –3.0 dex on that scale. Ignoring enhancement of carbon which ranges up to very large values, and two C-rich stars with very high N as well, there are 0 to 3 high or low strong outliers for each abundance ratio tested from Mg to Ni. The outliers have been checked and they are real. Ignoring the outliers, the dispersions are in most cases approximately consistent with the uncertainties, except those for [Sr/Fe] and [Ba/Fe], which are much larger. Approximately 6% of the sample are strong outliers in one or more elements between Mg and Ni. This rises to ∼15% if minor outliers for these elements and strong outliers for Sr and Ba are included. There are 6 stars with extremely low [Sr/Fe] and [Ba/Fe], including one which has lower [Ba/H] than Draco 119, the star found by Fulbright, Rich & Castro to have the lowest such ratio known previously. There is one extreme r-process star.

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