We present an analysis of the UVES high-resolution spectroscopic observations at the 8.2m VLT of J0023+0307 , a main-sequence extremely iron-poor dwarf star .
We are unable to detect iron lines in the spectrum but derive [ Fe/H ] < -6.1 from the Ca II resonance lines assuming [ Ca/Fe ] \geqslant 0.40 .
The chemical abundance pattern of J0023+0307 , with very low [ Fe/Mg ] and [ Ca/Mg ] abundance ratios , but relatively high absolute Mg and Si abundances , suggests J0023+0307 is a second generation star formed from a molecular cloud polluted by only one supernova in which the fall-back mechanism played a role .
We measure a carbon abundance of A ( C ) = 6.2 that places J0023+0307 on the “ low ” band in the A ( C ) - [ Fe/H ] diagram , suggesting no contamination from a binary companion .
This star is also unique having a lithium abundance ( A ( Li ) = 2.02 \pm 0.08 ) close to the level of the Lithium Plateau , in contrast with lower Li determinations or upper limits in all other extremely iron-poor stars .
The upper envelope of the lithium abundances in unevolved stars spanning more than three orders of magnitude in metallicity ( -6 < [ Fe/H ] < -2.5 ) defines a nearly constant value .
We argue that it is unlikely that such uniformity is the result of depletion processes in stars from a significantly higher initial Li abundance , but suggests instead a lower primordial production , pointing to new physics such as decaying massive particles , varying fundamental constants , or nuclear resonances , that could have affected the primordial ^ { 7 } Li production .