2006A&A...449..879L

Verification the theoretical prediction of oscillation of the fine-structure constant α (=e²/(h/2π)c) over cosmic time requires high precision Δα/α measurements at individual redshifts. In earlier studies the mean Δα/α values averaged over wide redshift intervals were usually reported. This requirement can be met using the single ion differential α measurement (SIDAM) procedure. We apply SIDAM to the FeII lines associated with the damped Lyα system observed at z_abs=1.15 in the spectrum of HE 0515-4414. The spectrum was obtained by means of the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT). The weighted mean <Δα/α> calculated using carefully selected 34 FeII pairs {λ1608,X} (X=2344, 2374, and 2586Å) is <Δα/α≥(-0.07±0.84)x10^–6 (1σ C.L.). The precision of this estimate improves by a factor of 2 the previous one reported for the same system. The obtained result represents an absolute improvement with respect to what has been done in the measurements of Δα/α.