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Large statistical samples of quasar spectra have previously indicated possible cosmological variations in the fine-structure constant, $alpha$. 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 spectras wavelength scales which would have caused significant systematic errors in our $alpha$ measurements. For each telescope we measure the relative deviation in $alpha$ from the current laboratory value, $Deltaalpha/alpha$, in 3 absorption systems at redshifts $z_{mathrm{abs}}=1.143$, 1.342, and 1.802. The nine measurements of $Deltaalpha/alpha$ are all consistent with zero at the 2-$sigma$ level, with 1-$sigma$ statistical (systematic) uncertainties 5.6--24 (1.8--7.0) parts per million (ppm). They are also consistent with each other at the 1-$sigma$ level, allowing us to form a combined value for each telescope and, finally, a single value for this line of sight: $Deltaalpha/alpha=-5.4 pm 3.3_{mathrm{stat}} pm 1.5_{mathrm{sys}}$ ppm, consistent with both zero and previous, large samples. We also average all Large Programme results measuring $Deltaalpha/alpha=-0.6 pm 1.9_{mathrm{stat}} pm 0.9_{mathrm{sys}}$ 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.
We present an accurate analysis of the H2 absorption lines from the zabs ~ 2.4018 damped Ly{alpha} system towards HE 0027-1836 observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT/UVES) as a part of the European Sou
Absorption line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, {alpha}, measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and
The Keck telescopes HIRES spectrograph has previously provided evidence for a smaller fine-structure constant, alpha, compared to the current laboratory value, in a sample of 143 quasar absorption systems: da/a=(-0.57+/-0.11)x10^{-5}. This was based
Consistency between cosmological data sets is essential for ongoing and future cosmological analyses. We first investigate the questions of stability and applicability of some moment-based inconsistency measures to multiple data sets. We show that th
Observations of metal absorption systems in the spectra of distant quasars allow to constrain a possible variation of the fine-structure constant throughout the history of the Universe. Such a test poses utmost demands on the wavelength accuracy and