We report a reanalysis of a near-pristine absorption system , located at a redshift z _ { abs } = 2.52564 toward the quasar Q1243 + 307 , based on the combination of archival and new data obtained with the HIRES echelle spectrograph on the Keck telescope .
This absorption system , which has an oxygen abundance [ O/H ] = -2.769 \pm 0.028 ( \simeq 1 / 600 of the solar abundance ) , is among the lowest metallicity systems currently known where a precise measurement of the deuterium abundance is afforded .
Our detailed analysis of this system concludes , on the basis of eight D i absorption lines , that the deuterium abundance of this gas cloud is \log _ { 10 } ( { D / H } ) = -4.622 \pm 0.015 , which is in very good agreement with the results previously reported by Kirkman et al. , but with an improvement on the precision of this single measurement by a factor of \sim 3.5 .
Combining this new estimate with our previous sample of six high precision and homogeneously analyzed D/H measurements , we deduce that the primordial deuterium abundance is \log _ { 10 } ( { D / H } ) _ { P } = -4.5974 \pm 0.0052 or , expressed as a linear quantity , 10 ^ { 5 } ( { D / H } ) _ { P } = 2.527 \pm 0.030 ; this value corresponds to a one percent determination of the primordial deuterium abundance .
Combining our result with a big bang nucleosynthesis ( BBN ) calculation that uses the latest nuclear physics input , we find that the baryon density derived from BBN agrees to within 2 \sigma of the latest results from the Planck cosmic microwave background data .