Probing the variability of the fine-structure constant with the VLT/UVES

We assess the cosmological variability of the fine-structure constant α from the analysis of an ensemble of Fe  λ1608, λ2344, λ2374, λ2383, λ2587, and λ2600 absorption lines at the redshift z = 1.15 toward the QSO HE 0515–4414 by means of the standard many-multiplet (MM) technique and its revision based on linear regression (RMM). This is the first time the MM technique is applied to exceptional high-resolution and high signal-to-noise QSO spectra recorded with the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT). Our analysis results in 〈∆α/α〉MM = (0.1 ± 1.7) · 10−6 and 〈∆α/α〉RMM = (−0.4 ± 1.9 ± 2.7sys) · 10−6, which are the most stringent bounds hitherto infered from an individual QSO absorption system. Our results support the null hypothesis 〈∆α/α〉 = 0 at a significance level of 91 percent, whereas the support for the result 〈∆α/α〉 = −5.7 · 10−6 presented in former MM studies is 12 percent.