We present a chemical abundance analysis of the faint halo metal-poor main-sequence star J0023+0307 , with \mbox { [ Fe / H ] } < -6.3 , based on a high-resolution ( R \sim 35 , 000 ) Magellan/MIKE spectrum .
The star was originally found to have \mbox { [ Fe / H ] } < -6.6 based on a Ca II K measurement in an R \sim 2 , 500 spectrum .
No iron lines could be detected in our MIKE spectrum .
Spectral lines of Li , C , Na , Mg , Al , Si , and Ca were detected .
The Li abundance is close to the Spite Plateau , \log \epsilon ( Li ) = 1.7 , not unlike that of other metal-poor stars although in stark contrast to the extremely low value found e.g. , in HE 1327 - 2326 at a similar [ Fe/H ] value .
The carbon G-band is detected and indicates strong C-enhancement , as is typical for stars with low Fe abundances .
Elements from Na through Si show a strong odd-even effect , and J0023 + 0307 displays the second-lowest known [ Ca/H ] abundance .
Overall , the abundance pattern of J0023+0307 suggests that it is a second-generation star that formed from gas enriched by a massive Population III first star exploding as a fall-back supernova The inferred dilution mass of the ejecta is 10 ^ { 5 \pm 0.5 } M _ { \odot } of hydrogen , strongly suggesting J0023+0307 formed in a recollapsed minihalo .
J0023 + 0307 is likely very old because it has a very eccentric orbit with a pericenter in the Galactic bulge .