A New Type of Extremely Metal Poor Star

We present an abundance analysis for the extremely metal poor star HE1424−0241 based on high dispersion spectra from HIRES at Keck. This star is a giant on the lower red giant branch with [Fe/H] ∼ −4.0 dex. Relative to Fe, HE1424−0241 has normal Mg, but it shows a very large deficiency of Si, with ǫ(Si)/ǫ(Fe) ∼ 1/10 and ǫ(Si)/ǫ(Mg) ∼ 1/25 that of all previously known extremely metal poor giants or dwarfs. It also has a moderately large deficiency of Ca and a smaller deficit of Ti, combined with enhanced Mn and Co and normal or low C. We suggest that in HE1424−0241 we see the effect of a very small number of contributing supernovae, and that the SNII contributing to the chemical inventory of HE1424−0241 were biased in progenitor mass or in explosion characteristics so as to reproduce its abnormal extremely low Si/Mg ratio. HE1424−0241 shows a deficiency of the explosive α-burning elements Si, Ca and Ti coupled with a ratio [Mg/Fe] normal for EMP stars; Mg is produced via hydrostatic α-burning. The latest models of nucleosynthesis in SNII fail to 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] 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]