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:

Abstract.A new molecular hydrogen cloud is found in the sub-damped Lyα absorber [log N(H ) = 19.88 ± 0.05] at the redshift z abs = 1.15 toward the bright quasar HE 0515-4414 (z em = 1.71). More than 30 absorption features in the Lyman band system of H 2 are identified in the UV spectrum of this quasar obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. The H 2 -bearing cloud shows a total H 2 column density N(H 2 ) = (8.716 cm −2 and a fractional molecular abundance f H 2 = (2.3 +2.3 −1.1 ) × 10 −3 derived from the H 2 lines arising from the J = 0 − 5 rotational levels of the ground electronic vibrational state. The estimated rate of photodissociation at the cloud edge I 0 < ∼ 1.8 × 10 −8 s −1 is much higher than the mean Galactic disk value, I MW ∼ 5.5 × 10 −11 s −1 . This may indicate an enhanced star-formation activity in the z = 1.15 system as compared with molecular clouds at z ∼ 3 where I ∼ I MW . We also find a tentative evidence that the formation rate coefficient of H 2 upon grain surfaces at z = 1.15 is a factor of 10 larger than a canonical Milky Way value, R MW ≈ 3 × 10 −17 cm 3 s −1 . The relative dust-to-gas ratio estimated from the [Cr/Zn] ratio is equal tok = 0.89 ± 0.19 (in units of the mean Galactic disk value), which is in good agreement with a high molecular fraction in this system. The estimated line-of-sight size of L ∼ 0.25 pc may imply that the H 2 is confined within small and dense filaments embedded in a more rarefied gas giving rise to the z = 1.15 sub-damped Lyα absorber.

Abstract. New high-resolution high signal-to-noise spectra of the z = 1.15 damped Lyman α (DLA) system toward the quasi-stellar object HE 0515-4414 reveal absorption lines of the multiplets 2 and 3 in C i. The resonance lines are seen in two components with total column densities of log N = 13.79 ± 0.01 and log N = 13.36 ± 0.01, respectively. The comparision of theoretical calculations of the relative fine-structure population with the ratios of the observed column densities suggests that the C i absorbing medium is either very dense or exposed to very intense UV radiation. The upper limit on the local UV energy density is 100 times the galactic UV energy density, while the upper limit on the H i number density is 110 cm −3 . The excitation temperatures of the ground state fine-structure levels of T = 15.7 and T = 11.1 K, respectively, are consistent with the temperature-redshift relation predicted by the standard Friedmann cosmology. The cosmic microwave background radiation (CMBR) is only a minor source of the observed fine-structure excitation.

Aims. We examine the ionization, abundances, and differential dust depletion of metals, the kinematic structure, and the physical conditions in the molecular hydrogen-bearing sub-damped Ly α system toward HE 0515−4414. Methods. We used the STIS and VLT UVES spectrographs to obtain high-resolution recordings of the damped Ly α profile and numerous associated metal lines. Observed element abundances were corrected with respect to dust depletion effects. Results. The sub-damped Ly α absorber at redshift z = 1.15 is unusual in several aspects. The velocity interval of associated metal lines extends for 700 km s Conclusions. The detection of H ii, as well as the large variation in dust depletion for this sight line, raises the question whether in future studies of damped Ly α systems ionization and depletion effects have to be considered in more detail. Ionization effects, for instance, may mimic an enrichment of α elements. An empirical recipe for detecting H ii regions is provided.