8 papers · 1 filter
Effects of correlated turbulent velocity fields on the formation of maser lines
R. Boeger, W. H. Kegel, M. Hegmann
The microturbulent approximation of turbulent motions is widely used in radiative transfer calculations. Mainly motivated by its simple computational application it is probably in…
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…
The D/H ratio at z=0.7 toward Q 1718+4807
Sergei A. Levshakov, Wilhelm H. Kegel, Fumio Takahara
The apparent discrepancy between low and high D abundances derived from QSO spectra may be caused by spatial correlations in the stochastic velocity field. If one accounts for such…
Primordial Deuterium Abundance Measurements
Sergei A. Levshakov, Wilhelm H. Kegel, Fumio Takahara
Deuterium abundances measured recently from QSO absorption-line systems lie in the range from 3 10^{-5} to 3 10^{-4}, which shed some questions on standard big bang theory. We show…
The primordial deuterium abundance : problems and prospects
Sergei A. Levshakov, Fumio Takahara, Wilhelm H. Kegel
The current status of extragalactic deuterium abundance is discussed using two examples of `low' and `high' D/H measurements. We show that the discordance of these two types of D a…