Publications (33)
Molecular hydrogen abundance in the dust-free damped Ly-alpha galaxy at z = 3.4
S. A. Levshakov, P. Molaro, M. Centurion +3
New results from the search for H2 absorption in the damped Ly-alpha galaxy at redshift z = 3.4 toward QSO 0000-2620 (z_em = 4.1) are reported. The high-resolution (lambda/Delta la…
Metal abundances and kinematics of quasar absorbers.- I. Absorption systems toward J2233-606
S. A. Levshakov, I. I. Agafonova, M. Centurion +1
The metal line profiles of different ions observed in high HI column density systems [N(HI) > 10^{16} cm^{-2}] in quasar spectra can be used to constrain the ionization structure a…
Relativistic ultrafast electron diffraction at high repetition rates
K. M. Siddiqui, D. B. Durham, F. Cropp +17
The ability to resolve the dynamics of matter on its native temporal and spatial scales constitutes a key challenge and convergent theme across chemistry, biology, and materials sc…
Spectral energy distribution of the metagalactic ionizing radiation field from QSO absorption spectra
I. I. Agafonova, M. Centurion, S. A. Levshakov +1
A computational procedure is presented to estimate the spectral shape of the ionizing background between 1 and 10 Ryd by analyzing optically thin absorption systems in the spectra…
An astrophysical oscillator strength for the SII 94.7 nm resonance line and S abundances in DLAs
P. Bonifacio, E. Caffau, M. Centurion +2
By using UV spectra for the O star HD 93521 taken with the ORFEUS II echelle spectrograph, we determine an ``astrophysical'' f value for the SII 94.7 nm line: f = 0.00498 (+0.00172…
The UVES Large Program for Testing Fundamental Physics II: Constraints on a Change in μ Towards Quasar HE 0027-1836
H. Rahmani, M. Wendt, R. Srianand +14
We present an accurate analysis of the H2 absorption lines from the zabs ~ 2.4018 damped Lyα system towards HE 0027-1836 observed with the Very Large Telescope Ultraviolet and Vis…
Conformer-specific Chemistry Imaged in Real Space and Time
E. G. Champenois, D. M. Sanchez, J. Yang +17
Conformational isomers or conformers of molecules play a decisive role in chemistry and biology. However, experimental methods to investigate chemical reaction dynamics are typical…
Imaging the Photochemical Ring-Opening of 1,3-Cyclohexadiene by Ultrafast Electron Diffraction
T. J. A. Wolf, D. M. Sanchez, J. Yang +20
The ultrafast photoinduced ring-opening of 1,3-cyclohexadiene constitutes a textbook example of electrocyclic reactions in organic chemistry and a model for photobiological reactio…
The UVES Large Program for testing fundamental physics - III. Constraints on the fine-structure constant from 3 telescopes
T. M. Evans, M. T. Murphy, J. B. Whitmore +10
Large statistical samples of quasar spectra have previously indicated possible cosmological variations in the fine-structure constant, . A smaller sample of higher signal-to-no…
Most precise single redshift bound to the variability of the fine-structure constant
S. A. Levshakov, M. Centurion, P. Molaro +4
Verification of theoretical predictions of an oscillating behavior of the fine-structure constant, alpha, with cosmic time requires high precision measurements at individual redshi…
Fundamental constants and high resolution spectroscopy
P. Bonifacio, H. Rahmani, J. B. Whitmore +14
Absorption-line systems detected in high resolution quasar spectra can be used to compare the value of dimensionless fundamental constants such as the fine-structure constant, alph…
The UVES Large Program for Testing Fundamental Physics: I Bounds on a change in alpha towards quasar HE 2217-2818
P. Molaro, M. Centurion, J. B. Whitmore +14
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.…
Imaging the Photochemistry of Cyclobutanone using Ultrafast Electron Diffraction: Experimental Results
A. E. Green, Y. Liu, F. Allum +27
We investigated the ultrafast structural dynamics of cyclobutanone following photoexcitation at nm using gas-phase megaelectronvolt ultrafast electron diffraction. Our inv…
VLT/UVES constraints on the carbon isotope ratio 12C/13C at z=1.15 toward the quasar HE 0515-4414
S. A. Levshakov, M. Centurion, P. Molaro +1
We analyzed the CI lines associated with the damped Ly-alpha system observed at zabs = 1.15 in the spectrum of HE 0515-4414 to derive the 12C/13C ratio. The spectrum was obtained b…
Nitrogen Abundances in Damped Ly alpha Galaxies
M. Centurion, P. Bonifacio, P. Molaro +1
Nitrogen abundances have been derived in Damped Ly alpha (DLA) galaxies at Zabs = 2.309, 2.827 and 3.025 toward the QSOs 0100+1300, 1425+6039 and 0347-3819 respectively. The behavi…
UVES observations of QSO 0000-2620: Molecular hydrogen abundance in the damped Ly-alpha system at z_abs = 3.3901
S. A. Levshakov, P. Molaro, M. Centurion +3
We have discovered molecular hydrogen in a fourth quasar damped Ly-alpha system (hereafter DLA). The UVES spectrograph on the 8.2m ESO Kueyen telescope has allowed the detection of…
Extinction and metal column density of HI regions up to redshift z~2
G. Vladilo, M. Centurion, S. A. Levshakov +4
We used the photometric database of the Sloan Digital Sky Survey (SDSS) to estimate the reddening of 13 SDSS quasars selected on the basis of the presence of zinc absorption lines…
A new measure of Delta alpha/alpha at redshift z = 1.84 from very high resolution spectra of Q1101-264
S. A. Levshakov, P. Molaro, S. Lopez +5
We probe the evolution of the fine-structure constant, alpha, with cosmic time. Accurate positions of the FeII lines 1608, 2382,and 2600 A are measured in the z = 1.84 absorption s…
UVES radial velocity accuracy from asteroid observations. Implications for the fine structure constant variability
P. Molaro, S. A. Levshakov, S. Monai +4
High resolution observations of the asteroids Iris and Juno have been performed by means of the UVES spectrograph at the ESO VLT to obtain the effective accurac y of the spectrogra…
VLT/UVES constraints on the cosmological variability of the fine-structure constant
S. A. Levshakov, M. Centurion, P. Molaro +1
We propose a new methodology for probing the cosmological variability of alpha from pairs of FeII lines (SIDAM, single ion differential alpha measurement) observed in individual ex…
VLT/Uves Observations of the Dla at Z=3.39 towards QSO 0000-2621
P. Molaro, P. Bonifacio, M. Centurion +3
UVES observations at ESO/VLT of the DLA at z=3.39 towards QSO 0000-2621 provided refined abundances for Fe, Si, N, Ni, and new abundances for O, Ar, P, Zn, Cr, H2. These determinat…
Nitrogen Abundances in High-z DLAs
P. Molaro, M. Centurion, V. D'Odorico +1
Determination of chemical abundances for elements produced mainly by Type I SNae and intermediate mass stars in high redshift DLAs probes the early chemical build-up on time-scales…
The O-Na and Mg-Al Anticorrelations in Turn-Off and early Subgiants in Globular Clusters
R. G. Gratton, P. Bonifacio, A. Bragaglia +16
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 subgiant branch in NGC6397 and NGC6752 were obtained with…
Early stages of Nitrogen enrichment in galaxies: Clues from measurements in damped Lyman alpha systems
M. Centurion, P. Molaro, G. Vladilo +3
We present 4 new measurements of nitrogen abundances and one upper limit in damped Lyman alpha absorbers (DLAs) obtained by means of high resolution (FWHM \~ 7 km/s) UVES/VLT spect…
The lithium content of the globular cluster NGC 6397
P. Bonifacio, L. Pasquini, F. Spite +16
We make use of high resolution, high signal-to-noise ratio spectra of 12 turn-off stars in the metal-poor globular cluster NGC 6397 to measure its lithium content. We conclude that…
The absorption system towards PKS 0118-272: A candidate Damped Ly system at low redshift
G. Vladilo, M. Centurion, R. Falomo +1
We present a spectroscopic and imaging study of the z=0.558 MgII absorption system towards the BL Lac PKS 0118-272. At the absorber redshift we detect lines of the low ionization s…
Limits on the spatial variations of the electron-to-proton mass ratio in the Galactic plane
S. A. Levshakov, D. Reimers, C. Henkel +4
Aims. To validate the Einstein equivalence principle (local position invariance) by limiting the fractional changes in the electron-to-proton mass ratio, mu = m_e/m_p, measured in…
VLT/UVES shows no cosmological variability of alpha
P. Molaro, M. Centurion, S. D'Odorico +1
The cosmological variability of alpha is probed from individual observations of pairs of FeII lines. This procedure allows a better control of the systematics and avoids the influe…
Abundances of metal-weak thick-disc candidates
P. Bonifacio, M. Centurion, P. Molaro
High resolution spectra of 5 candidate metal-weak thick-disc stars suggested by Beers & Sommer-Larsen (1995) are analyzed to determine their chemical abundances. The low abundance…
Extremely metal-poor Lyman limit system at z = 2.917 toward the quasar HE 0940-1050
S. A. Levshakov, I. I. Agafonova, M. Centurion +1
We report on detailed Monte Carlo inversion analysis of the Lyman limit system observed at z = 2.917 in the VLT/UVES spectrum of the quasar HE 0940-1050. Metal absorption lines of…
Optical follow-up of GRB 970508
T. J. Galama, P. J. Groot, J. van Paradijs +14
We report on the results of optical follow-up observations of the counterpart of GRB 970508, starting 7 hours after the event. Multi-color U, B, V, R and I band observa…
Heavy elements abundances in turn-off stars and early subgiants in NGC 6752
G. James, P. Francois, P. Bonifacio +12
High resolution spectra (R > 40 000) for 9 main sequence turn-off stars and 9 subgiants in the globular cluster NGC 6752 were acquired with UVES on the VLT-Kueyen (UT2). These data…
Most precise single redshift bound to Delta alpha/alpha
S. A. Levshakov, M. Centurion, P. Molaro +4
Verification of theoretical predictions of an oscillating behavior of the fine-structure constant alpha with cosmic time requires high precision Delta alpha/alpha measurements at i…