New Extremely Metal-Poor Stars in the Galactic Halo

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, four of which are new. Only stars with 4900 < Teff < 5650 K are included. Two stars of the eight are outliers in each of several abundance ratios. The most metal poor star in this sample, HE1424−0241, has [Fe/H] ∼ −4 dex and is thus among the most metal poor stars known in the Galaxy. It has highly anomalous abundance ratios unlike those of any other known EMP giant, with very low Si, Ca and Ti relative to Fe, and enhanced Mn and Co, again relative to Fe. Only (low) upper limits for C and N can be derived from the non-detection of the CH and NH molecular bands. 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 ([Fe/H] ∼ −3 dex), Based in part on observations obtained at the W.M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. Palomar Observatory, Mail Stop 105-24, California Institute of Technology, Pasadena, Ca., 91125, [email protected], [email protected] Carnegie Observatories of Washington, 813 Santa Barbara Street, Pasadena, Ca. 91101, andy, ian, [email protected] Current address: Department of Astronomy and Space Physics, Uppsala University, Box 515, 75120 Uppsala, Sweden, formerly at Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany, [email protected] Palomar Observatory, Mail Stop 105-24, California Institute of Technology, Pasadena, Ca., 91125, Current address: Australian National University, Australia, [email protected] Astrophysical Institute Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany, [email protected] Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany, [email protected]