The UVES Large Program for testing fundamental physics – III. Constraints on the fine-structure constant from three telescopes

Large statistical samples of quasar spectra have previously indicated possible cosmological variations in the fine-structure constant, . A smaller sample of higher signal-to-noise ratio spectra, with dedicated calibration, would allow a detailed test of this evidence. Towards that end, we observed equatorial quasar HS 1549+1919 with three telescopes: the Very Large Telescope, Keck and, for the first time in such analyses, Subaru. By directly comparing these spectra to each other, and by ‘supercalibrating’ them using asteroid and iodine-cell tests, we detected and removed long-range distortions of the quasar spectra’s wavelength scales which would have caused significant systematic errors in our measurements. For each telescope we measure the relative deviation in from the current laboratory value, = , in 3 absorption systems at redshifts zabs = 1:143, 1.342, and 1.802. The nine measurements of = are all consistent with zero at the 2- level, with 1- statistical (systematic) uncertainties 5.6‐ 24 (1.8‐7.0) parts per million (ppm). They are also consistent with each other at the 1level, allowing us to form a combined value for each telescope and, finally, a single value for this line of sight: = = 5:4 3:3stat 1:5sys ppm, consistent with both zero and previous, large samples. We also average all Large Programme results measuring = = 0:6 1:9stat 0:9sys ppm. Our results demonstrate the robustness and reliability at the 3 ppm level afforded by supercalibration techniques and direct comparison of spectra from different telescopes.