Deuterium to hydrogen towards QSO 1009+2956 from a mesoturbulent model

We present a new analysis of the deuterium absorption at z = 2.504 towards the quasar Q1009+2956 using the mesoturbulent model which accounts for possible correlations in the large scale velocity field. We obtain a slightly higher deuterium-tohydrogen ratio D/H ≃ (3.5 − 5.0) × 10 as compared with the recent measurement D/H = (3.3 − 4.5) × 10 (68% C.L.) performed by Burles & Tytler (1998b) using the usual microturbulent approximation which assumes that the velocity field is uncorrelated. Other mesoturbulent calculations of the D-abundances at z = 3.572 towards Q1937–1009 and at z = 0.701 towards Q1718+4807 (the systems showing ‘low’ and possibly ‘high’ D/H values, respectively, in the microturbulent approaches) agree with the present one within the errors of measurements. Thus, the mesoturbulent analysis does not reveal any spatial variations of D/H and supports the standard homogeneous model of big bang nucleosynthesis. Subject headings: cosmology: observations — methods: data analysis — quasars: absorption lines — quasars: individual (1009+2956)