Abstract. High dispersion spectra (R ∼ > 40 000) for a quite large number of stars at the main sequence turn-off and at the base of the giant branch in NGC 6397 and NGC 6752 were obtained with the UVES on Kueyen (VLT UT2). The [Fe/H] values we found are −2.03 ± 0.02 ± 0.04 and −1.42 ± 0.02 ± 0.04 for NGC 6397 and NGC 6752 respectively, where the first error bars refer to internal and the second ones to systematic errors (within the abundance scale defined by our analysis of 25 subdwarfs with good Hipparcos parallaxes). In both clusters the [Fe/H]'s obtained for TO-stars agree perfectly (within a few percent) with that obtained for stars at the base of the RGB. The [O/Fe] = 0.21 ± 0.05 value we obtain for NGC 6397 is quite low, but it agrees with previous results obtained for giants in this cluster. Moreover, the star-to-star scatter in both O and Fe is very small, indicating that this small mass cluster is chemically very homogenous. On the other hand, our results show clearly and for the first time that the O-Na anticorrelation (up to now seen only for stars on the red giant branches of globular clusters) is present among unevolved stars in the globular cluster NGC 6752, a more massive cluster than NGC 6397. A similar anticorrelation is present also for Mg and Al, and C and N. It is very difficult to explain the observed Na-O, and Mg-Al anticorrelation in NGC 6752 stars by a deep mixing scenario; we think it requires some non internal mechanism.

We analyze extant data of Al`2, Al`, and other low ions with the aim of studying the ionization properties of damped Lya systems (DLAs) from the analysis of the ratio R(Al`2/Al`) 4 N(Al`2)/N(Al`). We Ðnd the good correlations log N(Al`)Èlog N(Si`) and log N(Al`)Èlog N(Fe`) that we use to indirectly estimate N(Al`) from N(Si`) and/or N(Fe`) measurements. In this way, we determine the ratio R(Al`2/Al`) for a sample of 20 DLAs. Contrary to common belief, the ratio can attain relatively high values (up to 0.6), suggesting that the gas of the intermediate ionization state plays an important role in DLAs. On the other hand, the lack of any trend between abundance ratios, such as Si/H and Si/Fe and R(Al`2/Al`) indicates that abundances are not severely inÑuenced by ionization e †ects. We Ðnd a log R(Al`2/Al`)Èlog N(H0) anticorrelation that we use in conjunction with idealized photoionization equilibrium calculations to constrain the ionization properties and to predict ionization corrections in DLAs. We consider two possible origins for the species of the low-and intermediate-ionization state : (1) neutral regions devoid of Al`2 and/or (2) partially ionized, Al`2-bearing regions. The log R(Al`2/Al`)È log N(H0) anticorrelation can be naturally explained in terms of a two-region model with a soft, stellartype ionizing radiation Ðeld. We present abundance ionization corrections for 14 elements of astrophysical interest derived with di †erent types of ionizing spectra. For most of these elements, the corrections are generally below measurements errors, which is contrary to the predictions of recent models presented in the literature. We brieÑy discuss the potential e †ects of inaccuracies in the Al recombination rates used in the photoionization calculations.

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 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.

Abstract. We present 4 new measurements of nitrogen abundances and one upper limit in damped Ly α absorbers (DLAs) obtained by means of high resolution (FWHM ≃ 7 km s −1 ) UVES/VLT spectra. In addition to these measurements we have compiled data from all DLAs with measurements of nitrogen and α-capture elements (O, S or Si) available in the literature, including all HIRES/Keck and UVES/VLT data for a total of 33 systems, i.e. the largest sample investigated so far. We find that [N/α]