Abstract.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) × 10and ∆α/α RMM = (−0.4 ± 1.9 ± 2.7 sys ) × 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.

Aims. Verification the theoretical prediction of oscillation of the fine-structure constant α (≡e 2 / c) over cosmic time requires high precision ∆α/α measurements at individual redshifts. In earlier studies the mean ∆α/α values averaged over wide redshift intervals were usually reported. This requirement can be met using the single ion differential α measurement (SIDAM) procedure. We apply SIDAM to the Fe ii lines associated with the damped Lyα system observed at z abs = 1.15 in the spectrum of HE 0515-4414. Methods. The spectrum was obtained by means of the UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT).Results. The weighted mean ∆α/α calculated using carefully selected 34 Fe ii pairs {λ1608, X} (X = 2344, 2374, and 2586 Å) is ∆α/α = (−0.07 ± 0.84) × 10 −6 (1σ C.L.). The precision of this estimate improves by a factor of 2 the previous one reported for the same system. The obtained result represents an absolute improvement with respect to what has been done in the measurements of ∆α/α .

Aims. We present a detailed analysis of a very high resolution (R ≈ 112 000) spectrum of the quasar HE 0515−4414 obtained using the High Accuracy Radial velocity Planet Searcher (HARPS) mounted on the ESO 3.6 m telescope at the La Silla observatory. The main aim is to use a HARPS spectrum of very high wavelength calibration accuracy (better than 1 mÅ), to constrain the variation of α ≡ e 2 / c and investigate any possible systematic inaccuracies in the wavelength calibration of the UV Echelle Spectrograph (UVES) mounted on the ESO Very Large Telescope (VLT). Methods. A cross-correlation analysis between the Th-Ar lamp spectra obtained with HARPS and UVES is carried out to detect any possible shift between the two spectra. Absolute wavelength calibration accuracies, and how that translates into the uncertainties in ∆α/α are computed using Gaussian fits for both lamp spectra. The value of ∆α/α at z abs = 1.1508 is obtained using the many multiplet method and simultaneous Voigt profile fits of HARPS and UVES spectra. Results. We find the shift between the HARPS and UVES spectra has a mean around zero with a dispersion of σ 1 mÅ. This is shown to be well within the wavelength calibration accuracy of UVES (i.e. σ 4 mÅ). We show that the uncertainties in the wavelength calibration induce an error of about ∆α/α ≤ 10 −6 in determining the variation of the fine-structure constant. Thus, the results of non-evolving ∆α/α reported in the literature based on UVES/VLT data should not be heavily influenced by problems related to wavelength calibration uncertainties. Our higher resolution spectrum of the z abs = 1.1508 Damped Lyman-α system toward HE 0515−4414 reveals more components compared to the UVES spectrum. Using only Fe ii lines of the z abs = 1.1508 system, we obtain ∆α/α = (0.05 ± 0.24) × 10 −5 . This result is consistent with the earlier measurement for this system using the UVES spectrum alone.

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Abstract. We present constraints on the cosmological constant λ 0 from gravitational lensing statistics of the Jodrell Bank-VLA Astrometric Survey (JVAS). Although this is the largest gravitational lens survey which has been analysed, cosmological constraints are only comparable to those from optical surveys. This is due to the fact that the median source redshifts of JVAS are lower, which leads to both relatively fewer lenses in the survey and a weaker dependence on the cosmological parameters. Although more approximations have to be made than is the case for optical surveys, the consistency of the results with those from optical gravitational lens surveys and other cosmological tests indicate that this is not a major source of uncertainty in the results. However, joint constraints from a combination of radio and optical data are much tighter. Thus, a similar analysis of the much larger Cosmic Lens All-Sky Survey should provide even tighter constraints on the cosmological constant, especially when combined with data from optical lens surveys.At 95% confidence, our lower and upper limits on λ 0 − Ω 0 , using the JVAS lensing statistics information alone, are respectively −2.69 and 0.68. For a flat universe, these correspond to lower and upper limits on λ 0 of respectively −0.85 and 0.84. Using the combination of JVAS lensing statistics and lensing statistics from the literature as discussed in Quast & Helbig (1999) the corresponding λ 0 − Ω 0 values are −1.78 and 0.27. For a flat universe, these correspond to lower and upper limits on λ 0 of respectively −0.39 and 0.64.Send offprint requests to: P. Helbig Present Address: