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 $\ion{Fe}{ii}$ $\lambda1608$, $\lambda2344$, $\lambda2374$, $\lambda2383$, $\lambda2587$, and $\lambda2600$ 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 $\langle\Delta\alpha/\alpha\rangle_\mathrm{MM}=(0.1\pm1.7) \times10^{-6}$ and $\langle\Delta\alpha/\alpha\rangle_\mathrm{RMM}=(-0.4 \pm1.9\pm2.7_\mathrm{sys})\times10^{-6}$, which are the most stringent bounds hitherto infered from an individual QSO absorption system. Our results support the null hypothesis $\langle\Delta\alpha/\alpha\rangle=0$ at a significance level of 91 percent, whereas the support for the result $\langle\Delta\alpha/\alpha\rangle=-5.7\times10^{-6}$ presented in former MM studies is 12 percent.