New Extremely Metal-Poor Stars in the Galactic Halo

Abstract

We present a detailed abundance analysis based on high resolution and high signal-to-noise spectra of eight extremely metal poor (EMP) stars with [Fe/H] < -3.5$dex,fourofwhicharenew.Onlystarswith4900<Teff<5650Kareincluded.Twostarsoftheeightareoutliersineachofseveralabundanceratios.Themostmetalpoorstarinthissample,HE1424-0241,has[Fe/H]-4dexandisthusamongthemostmetalpoorstarsknownintheGalaxy.IthashighlyanomalousabundanceratiosunlikethoseofanyotherknownEMPgiant,withverylowSi,CaandTirelativetoFe,andenhancedMnandCo,againrelativetoFe.Only(low)upperlimitsforCandNcanbederivedfromthenon-detectionoftheCHandNHmolecularbands.HE0132$-$2429, another sample star, has excesses of N and Sc with respect to Fe. The strong outliers in abundance ratios among the Fe-peak elements in these C-normal stars, not found at somewhat higher metallicities, are definitely real. They suggest that at such low metallicities we are beginning to see the anticipated and long sought stochastic effects of individual supernova events contributing to the Fe-peak material within a single star. A detailed comparison of the results of the analysis procedures adopted by our 0Z project compared to those of the First Stars VLT Large Project finds a systematic difference for [Fe/H] of ~0.3 dex, our values always being higher.

Accepted to the ApJ

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• Multi-Element Abundance Measurements from Medium-Resolution Spectra. II. Catalog of Stars in Milky Way Dwarf Satellite Galaxies
• Integrated Nucleosynthesis in Neutrino Driven Winds
• Stellar Archaeology -- Exploring the Universe with Metal-Poor Stars
• Metal-Free Gas Supply at the Edge of Reionization: Late-Epoch Population III Star Formation
• A new imprint of fast rotators: low 12C/13C ratios in extremely metal-poor halo stars
• Abundances of Sr, Y, and Zr in Metal-Poor Stars and Implications for Chemical Evolution in the Early Galaxy