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The primordial deuterium abundance probes fundamental physics during the BigBang Nucleosynthesis and can be used to infer cosmological parameters.Observationally, the abundance can be measured using absorbing clouds along thelines of sight to distant quasars. Observations of the quasar PKS1937--101contain two absorbers for which the deuterium abundance has previously beendetermined. Here we focus on the higher redshift one at $z_{abs} = 3.572$. Wepresent new observations with significantly increased signal-to-noise ratiowhich enable a far more precise and robust measurement of the deuterium tohydrogen column density ratio, resulting in D/H = $2.62\pm0.05\times10^{-5}$.This particular measurement is of interest because it is among the most preciseassessments to date and it has been derived from the second lowestcolumn-density absorber [N(HI) $=17.9\mathrm{cm}^{-2}$] that has so-far beenutilised for deuterium abundance measurements. The majority of existinghigh-precision measurements were obtained from considerably higher columndensity systems [i.e. N(HI) $>19.4\mathrm{cm}^{-2}$]. This bodes well forfuture observations as low column density systems are more common.

A precise deuterium abundance: Re-measurement of the z=3.572 absorption system towards the quasar PKS1937-101