Context. Absorption-line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, α, measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and also spatial variations in α on cosmological scales. These variations may reach a fractional level of ≈10 ppm (parts per million). Aims. To test these claims we are conducting a Large Program of observations with the Very Large Telescope's Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high-resolution (R ≈ 60 000) and high signal-to-noise ratio (S /N ≈ 100) UVES spectra calibrated specifically for this purpose. Here we analyse the first complete quasar spectrum from this programme, that of HE 2217−2818. Methods. We applied the many multiplet method to measure α in five absorption systems towards this quasar: z abs = 0.7866, 0.9424, 1.5558, 1.6279 , and 1.6919. Results. The most precise result is obtained for the absorber at z abs = 1.6919 where 3 Fe  transitions and Al  λ1670 have high S/N and provide a wide range of sensitivities to α. The absorption profile is complex with several very narrow features, and it requires 32 velocity components to be fitted to the data. We also conducted a range of tests to estimate the systematic error budget. Our final result for the relative variation in α in this system is ∆α/α = +1.3 ± 2.4 stat ± 1.0 sys ppm. This is one of the tightest current bounds on α-variation from an individual absorber. A second, separate approach to the data reduction, calibration, and analysis of this system yielded a slightly different result of −3.8 ± 2.1 stat ppm, possibly suggesting a larger systematic error component than our tests indicated. This approach used an additional 3 Fe  transitions, parts of which were masked due to contamination by telluric features. Restricting this analysis to the Fe  transitions alone and using a modified absorption profile model gave a result that is consistent with the first approach, ∆α/α = +1.1 ± 2.6 stat ppm. The four other absorbers have simpler absorption profiles, with fewer and broader features, and offer transitions with a narrower range of sensitivities to α. They therefore provide looser bounds on ∆α/α at the > ∼ 10 ppm precision level. Conclusions. The absorbers towards quasar HE 2217−2818 reveal no evidence of any variation in α at the 3-ppm precision level (1σ confidence). If the recently reported 10-ppm dipolar variation in α across the sky is correct, the expectation at this sky position is (3.2−5.4) ± 1.7 ppm depending on dipole model used. Our constraint of ∆α/α = +1.3 ± 2.4 stat ± 1.0 sys ppm is not inconsistent with this expectation.

We report on an attempt to accurately wavelength calibrate four nights of data taken with the Keck HIRES spectrograph on QSO PHL957, for the purpose of determining whether the fine structure constant was different in the past. Using new software and techniques, we measured the redshifts of various Ni II, Fe II, Si II, etc. lines in a damped Lyα system at z = 2.309. Roughly half the data were taken through the Keck iodine cell which contains thousands of well calibrated iodine lines. Using these iodine exposures to calibrate the normal Th-Ar Keck data pipeline output we found absolute wavelength offsets of 500 m/s to 1000 m/s with drifts of more than 500 m/s over a single night, and drifts of nearly 2000 m/s over several nights. These offsets correspond to an absolute redshift of uncertainty of about ∆z ≈ 10 −5 (∆λ ≈ 0.02Å), with daily drifts of around ∆z ≈ 5 × 10 −6 (∆λ ≈ 0.01Å), and multiday drifts of nearly ∆z ≈ 2 × 10 −5 (≈ 0.04Å). The causes of the wavelength offsets are not known, but since claimed shifts in the fine structure constant would result in velocity shifts of less than 100 m/s, this level of systematic uncertainty may make it difficult to use Keck HIRES data to constrain the change in the fine structure constant. Using our calibrated data, we applied both our own fitting software and standard fitting software to measure ∆α α , but discovered that we could obtain results ranging from significant detection of either sign, to strong null limits, depending upon which sets of lines and which fitting method was used. We thus speculate that the discrepant results on ∆α α reported in the literature may be due to random fluctuations coming from under-estimated systematic errors in wavelength calibration and fitting procedure.

We present an accurate analysis of the H 2 absorption lines from the z abs ∼ 2.4018 damped Lyαsystem towards HE 0027−1836 observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT/UVES) as a part of the European Southern Observatory Large Programme "The UVES large programme for testing fundamental physics" to constrain the variation of proton-to-electron mass ratio, µ ≡ m p /m e . We perform cross-correlation analysis between 19 individual exposures taken over three years and the combined spectrum to check the wavelength calibration stability. We notice the presence of a possible wavelength dependent velocity drift especially in the data taken in 2012. We use available asteroids spectra taken with UVES close to our observations to confirm and quantify this effect. We consider single and two component Voigt profiles to model the observed H 2 absorption profiles. We use both linear regression analysis and Voigt profile fitting where ∆µ/µ is explicitly considered as an additional fitting parameter. The two component model is marginally favored by the statistical indicators and we get ∆µ/µ = −2.5 ± 8.1 stat ± 6.2 sys ppm. When we apply the correction to the wavelength dependent velocity drift we find ∆µ/µ = −7.6 ± 8.1 stat ± 6.3 sys ppm. It will be important to check the extent to which the velocity drift we notice in this study is present in UVES data used for previous ∆µ/µ measurements.

We present a new 'supercalibration' technique for measuring systematic distortions in the wavelength scales of high resolution spectrographs. By comparing spectra of 'solar twin' stars or asteroids with a reference laboratory solar spectrum, distortions in the standard thoriumargon calibration can be tracked with ∼10 m s −1 precision over the entire optical wavelength range on scales of both echelle orders (∼50-100 Å) and entire spectrographs arms (∼1000-3000 Å). Using archival spectra from the past 20 years we have probed the supercalibration history of the VLT-UVES and Keck-HIRES spectrographs. We find that systematic errors in their wavelength scales are ubiquitous and substantial, with long-range distortions varying between typically ±200 m s −1 per 1000 Å. We apply a simple model of these distortions to simulated spectra that characterize the large UVES and HIRES quasar samples which previously indicated possible evidence for cosmological variations in the fine-structure constant, α. The spurious deviations in α produced by the model closely match important aspects of the VLT-UVES quasar results at all redshifts and partially explain the HIRES results, though not self-consistently at all redshifts. That is, the apparent ubiquity, size and general characteristics of the distortions are capable of significantly weakening the evidence for variations in α from quasar absorption lines.

Large statistical samples of quasar spectra have previously indicated possible cosmological variations in the fine-structure constant, α. 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 α measurements. For each telescope we measure the relative deviation in α from the current laboratory value, ∆α/α, in 3 absorption systems at redshifts z abs = 1.143, 1.342, and 1.802. The nine measurements of ∆α/α are all consistent with zero at the 2-σ level, with 1-σ statistical (systematic) uncertainties 5.6-24 (1.8-7.0) parts per million (ppm). They are also consistent with each other at the 1-σ level, allowing us to form a combined value for each telescope and, finally, a single value for this line of sight: ∆α/α = −5.4 ± 3.3 stat ± 1.5 sys ppm, consistent with both zero and previous, large samples. We also average all Large Programme results measuring ∆α/α = −0.6±1.9 stat ±0.9 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.