VLT / UVES constraints on the cosmological variability of the fine - structure constant ⋆

A differential many-multiplet (DMM) technique is developed to probe the variability of α. Applied to the Fe ii lines of the metal absorption line system at z abs = 1.839 in the spectrum of Q1101–264 obtained by means of the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT), the DMM provides ∆α/α = (2.4 ± 3.8stat) × 10 −6. The z abs = 1.15 Fe ii system toward HE0515–4414 has been re-analyzed by the DMM method thus obtaining for the combined sample ∆α/α = (0.4 ± 1.5stat) × 10 −6. These values are shifted with respect to the Keck/HIRES mean ∆α/α = (−5.7 ± 1.1stat) × 10 −6 (Murphy et al. 2004) at very high confidence level (95%). The fundamental photon noise limitation in the ∆α/α measurement with the VLT/UVES is discussed to figure the prospects for future observations. It is suggested that with a spectrograph of ∼ 10 times the UVES resolution coupled to a 100 m class telescope the present Oklo level (∆α/α ≥ 4.5 × 10 −8) can be achieved along cosmological distances with differential measurements of ∆α/α .