Raghunathan Srianand

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Development of fundamental physics relies on the constancy of various fundamental quantities such as the fine structure constant. Detecting or constraining the possible time variations of these fundamental physical quantities is an important step toward a complete understanding of basic physics. High quality absorption lines seen in the spectra of distant(More)
We present the results of a search for damped Lyman-α (DLA) systems in the Sloan Digital Sky Survey II (SDSS), Data Release 7. We use a fully automatic procedure to identify DLAs and derive their column densities. The procedure is checked against the results of previous searches for DLAs in SDSS. We discuss the agreements and differences and show the(More)
A new constraint on the time dependence of the proton−to−electron mass ratio Abstract. A new limit on the possible cosmological variation of the proton-to-electron mass ratio µ = mp/me is estimated by measuring wavelengths of H2 lines of Lyman and Werner bands from two absorption systems at z abs = 2.5947 and 3.0249 in the spectra of quasars Q 0405−443 and(More)
Memorie della The UVES large program for testing fundamental physics II: constraints ∆µ/µ towards quasar HE 0027 − 1836 Abstract. We study the variation of proton-to-electron mass ratio, µ, using the H 2 absorption lines from the z abs ∼ 2.4018 DLA system towards HE 0027 − 1836 observed with the VLT/UVES as a part of the ESO Large Program for testing(More)
We report a new constraint on the variation of the fine-structure constant based on the analysis of 15 Si iv doublets selected from a ESO-UVES sample. We find ∆α/α = (+0.15 ± 0.43) × 10 −5 over a redshift range of 1.59 ≤ z ≤ 2.92 which is consistent with no variation in α. This result represents a factor three improvement on the constraint on ∆α/α based on(More)
We present the direct detection of molecular hydrogen at the highest red-shift known today (z abs = 4.224) in a Damped Lyman-α (DLA) system toward the quasar PSS J 1443+2724. This absorber is remarkable for having one of the highest metallicities amongst DLA systems at z abs > 3, with a measured iron abundance relative to Solar of −1.12 ± 0.10. We provide(More)
While gravitationally lensed quasars are expected to display an odd number of images, invariably systems are observed with an even number of quasars. For this, lensing galaxies must have very small core radii; this provides strong demagnification of one of the images. High resolution imaging of the gravitationally lensed BAL quasar, APM08279+5255, reveals(More)
We used our database of VLT-UVES quasar spectra to build up a sample of 70 Damped Lyman-α (DLA) or strong sub-DLA systems with total neutral hydrogen column densities of log N(H ) > ∼ 20 and redshifts in the range 1.7 < z abs < 4.3. For each of the systems, we measured in an homogeneous manner the metallicities relative to Solar, [X/H] (with X = Zn, or S(More)