112 citations · 699 across the 27 of their papers we have counts for
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Quasar spectral energy distribution in EUV restored from associated absorbers: indications to the HeII opacity of the quasar accretion disk wind
S. A. Levshakov, I. I. Agafonova, D. Reimers +2
(abridged) Aims. To reconstruct the spectral shape of the quasar ionizing radiation in the extreme-UV range (1Ryd <= E < 10Ryd) from the analysis of narrow absorption lines (NAL) o…
Bounds on the fine structure constant variability from FeII absorption lines in QSO spectra
Paolo Molaro, Dieter Reimers, Irina I. Agafonova +1
The Single Ion Differential alpha Measurement (SIDAM) method for measuring fine stucture variations (daa)and its figures of merit are illustrated together with the results produced…
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…
Spectral shape of the UV ionizing background and HeII absorption at redshifts 1.8 < z < 2.9
I. I. Agafonova, S. A. Levshakov, D. Reimers +4
The shape of the UV ionizing background is reconstructed from optically thin metal absorption-line systems identified in spectra of HE2347-4342, Q1157+3143, and HS1700+6416 in the…
Spectral shape of the UV ionizing background and OVI absorbers at z ~ 1.5 towards HS0747+4259
D. Reimers, I. I. Agafonova, S. A. Levshakov +5
We report on high resolution spectra of the bright QSO HS0747+4259 (zem = 1.90, V = 15.8) observed to search for intermediate redshift OVI absorption systems. The spectra were obta…
Nitrogen-deficient and iron-rich associated absorbers with oversolar metallicities towards the quasar HE0141-3932
S. A. Levshakov, I. I. Agafonova, D. Reimers +3
HE0141-3932 (zem=1.80) is a bright blue radio-quite quasar which reveals an emission line spectrum with an unusually weak Ly-alpha line. In addition, large redshift differences (De…
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…
HE 0141-3932: a bright QSO with an unusual emission line spectrum and associated absorption
D. Reimers, E. Janknecht, C. Fechner +3
HE 0141-3932 (zem = 1.80) is a bright blue radio-quite quasar with an unusually weak Ly-alpha emission line. Large redshift differences (Delta z = 0.05) are observed between high i…
The broad OVI absorber at z = 3.02 toward CTQ 325
S. A. Levshakov, S. D'Odorico, I. I. Agafonova +1
We report on the multiphase absorption-line system detected at a redshift z = 3.021 in the spectrum of the quasi-stellar object CTQ 325 (z_em = 3.212). The system is displaced by ~…
Photoionized OVI absorbers toward the bright QSO HE 0515-4414
S. A. Levshakov, I. I. Agafonova, D. Reimers +1
We report on detailed Monte Carlo inversion analysis of five OVI systems from the spectrum of the bright quasar HE 0515-4414 (z_e = 1.71). The associated system at z_a = 1.697 with…
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…
Metal abundances and kinematics of quasar absorbers - II. Absorption systems toward Q0347-3819 and APM BR J0307-4945
S. A. Levshakov, I. I. Agafonova, S. D'Odorico +2
Detailed Monte Carlo Inversion analysis of the spectral lines from three Lyman limit systems (LLS) [N(HI) > 10^{17} cm^-2] and nine lower N(HI) systems [2 10^{14} < N(HI) < 2 10^{1…
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…
Argon and Silicon abundances in the damped Ly-alpha system I Zw 18
S. A. Levshakov, W. H. Kegel, I. I. Agafonova
We show that the difference between the Ar and Si relative abundance ratio derived from FUSE absorption spectra and from the HII regions of I Zw 18 is a consequence of the microtur…
Monte Carlo inversion of hydrogen and metal lines from QSO absorption spectra
Sergei A. Levshakov, Irina I. Agafonova, Wilhelm H. Kegel
A new method, based on the simulated annealing algorithm and aimed at the inverse problem in the analysis of intergalactic (interstellar) complex spectra of hydrogen and metal line…
On the deuterium abundance at z_a = 3.514 towards APM 08279+5255
S. A. Levshakov, I. I. Agafonova, W. H. Kegel
A very low primordial deuterium abundance of D/H = 1.5 10^{-5} has recently been proposed by Molaro et al. in the Lyman limit system with log(N_HI) = 18.1 cm^{-2} at z_a = 3.514 to…
Measurability of kinetic temperature from metal absorption-line spectra formed in chaotic media
Sergei A. Levshakov, Fumio Takahara, Irina I. Agafonova
We present a new method for recovering the kinetic temperature of the intervening diffuse gas to an accuracy of 10%. The method is based on the comparison of unsaturated absorption…