New extremely metal-poor stars in the Galactic halo

作者：Cohen Judith G^*; Christlieb Norbert; McWilliam Andrew; Shectman Stephen; Thompson Ian; Melendez Jorge; Wisotzki Lutz; Reimers Dieter

来源：Astrophysical Journal, 2008, 672(1): 320-341.

DOI：10.1086/523638

• nuclear reactions
• nucleosynthesis
• abundances
• stars : abundances
• supernovae : general Online material : machine-readable table

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] less than or similar to 3.5 dex, four of which are new. Only stars with 4900 K < T-eff < 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, HE 1424-0241, has [Fe/H] similar to -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 nondetection of the CH and NH molecular bands. HE 0132-2429, 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] similar to -3 dex), 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. With spectra reaching well into the near-UV we are able to probe the behavior of copper abundances in such extreme EMP stars. 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 similar to 0.3 dex, our values always being higher.

• 出版日期2008-1-1