We present the elemental abundances of HE 1327 - 2326 , the most iron-deficient star known , determined from a comprehensive analysis of spectra obtained with the Subaru Telescope High Dispersion Spectrograph .
HE 1327 - 2326 is either in its main sequence or subgiant phase of evolution .
Its NLTE corrected iron abundance is [ Fe/H ] = -5.45 , 0.2 dex lower than that of HE 0107 - 5240 , the previously most iron-poor object known , and more than 1 dex lower than those of all other metal-poor stars .
Both HE 1327 - 2326 and HE 0107 - 5240 exhibit extremely large overabundances of carbon ( [ C/Fe ] \sim + 4 ) .
The combination of extremely high carbon abundance with outstandingly low iron abundance in these objects clearly distinguishes them from other metal-poor stars .
The large carbon excesses in these two stars are not the result of a selection effect .

There also exist important differences between HE 1327 - 2326 and HE 0107 - 5240 .
While the former shows remarkable overabundances of the light elements ( N , Na , Mg and Al ) , the latter shows only relatively small excesses of N and Na .
The neutron-capture element Sr is detected in HE 1327 - 2326 , but not in HE 0107 - 5240 ; its Sr abundance is significantly higher than the upper limit for HE 0107 - 5240 .
The Li i 6707 Å line , which is detected in most metal-poor dwarfs and warm subgiants having the same temperature as HE 1327 - 2326 , is not found in this object .
The upper limit of its Li abundance ( \log \epsilon \left ( \mbox { Li } \right ) < 1.5 ) is clearly lower than the Spite plateau value .

These data provide new constraints on models of nucleosynthesis processes in the first generation objects that were responsible for metal enrichment at the earliest times .
We discuss possible scenarios to explain the observed abundance patterns .