An abundance study of the most iron-poor star HE1327-2326 with Subaru/HDS

We present an elemental abundance analysis of HE 1327-2326, the most iron-deficient star known, based on a comprehensive investigation of spectra obtained with the Subaru Telescope. HE 1327-2326 is either in its main sequence or subgiant phase of evolution, hence it is essentially unevolved. The chemical abundances of this star have the following properties, which provide new constraints on models of nucleosynthesis processes that occurred in first-generation objects: (1)The iron abundance (NLTE) is [Fe/H]= -5.45. This value is 0.2 dex lower than that of HE 0107-5240, the previously most iron-poor object known. No object having [Fe/H]= -5 ∼ -4 is known to date. (2)This star, as well as HE 0107-5240, exhibits extremely large overabundances of carbon relative to solar ratios ([C/Fe]∼ +4). (3)HE 1327-2326 exhibits remarkable overabundances of the light elements (N, Na, Mg and Al), while HE 0107-5240 shows only relatively small excesses of N and Na. (4)A large overabundance of Sr is found in HE 1327-2326 as compared to other extremely low metallicity stars. (5)The Li I 6707 Å line, which is detected in the great majority of metal-poor dwarfs and warm subgiants, is not found in HE 1327-2326. The upper limit on the Li abundance we determine (log ε (Li) < 1.5) is clearly lower than the expected value from the Spite plateau.