40 research outputs found
Measurability of kinetic temperature from metal absorption-line spectra formed in chaotic media
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-line profiles of two species with
different atomic weights. The species are assumed to have the same temperature
and bulk motion within the absorbing region. The computational technique
involves the Fourier transform of the absorption profiles and the consequent
Entropy-Regularized chi^2-Minimization [ERM] to estimate the model parameters.
The procedure is tested using synthetic spectra of CII, SiII and FeII ions. The
comparison with the standard Voigt fitting analysis is performed and it is
shown that the Voigt deconvolution of the complex absorption-line profiles may
result in estimated temperatures which are not physical. We also successfully
analyze Keck telescope spectra of CII1334 and SiII1260 lines observed at the
redshift z = 3.572 toward the quasar Q1937--1009 by Tytler {\it et al.}.Comment: 25 pages, 6 Postscript figures, aaspp4.sty file, submit. Ap
Probing the variability of the fine-structure constant with the VLT/UVES
We assess the cosmological variability of the fine-structure constant from
the analysis of an ensemble of Fe II absorption lines at the redshift z=1.15
toward the QSO HE 0515-4414 by means of the standard many-multiplet (MM)
technique and its revision based on linear regression (RMM). This is the first
time the MM technique is applied to exceptional high-resolution and high
signal-to-noise QSO spectra recorded with the UV-Visual Echelle Spectrograph
(UVES) at the ESO Very Large Telescope (VLT). Our analysis results in the most
stringent bounds hitherto infered from QSO absorption lines. Our results
support the null hypothesis of a non-varying fine-structure constant at a
significance level of 91 percent, whereas the support for the results presented
in former MM studies indicating a variation in the fine-structure constant is
12 percent.Comment: 7 pages, 5 figures, accepted for publication in Astronomy &
Astrophysics Letter
The D/H ratio at z = 3.57 toward Q 1937-1009
Deuterium abundance re-measurements by Burles and Tytler (1998; hereafter BT)
yielded D/H = (3.3 +/- 0.3) 10^{-5} and the robust upper limit D/H < 3.9
10^{-5} from the z_a = 3.572 system toward Q1937-1009. In this new analysis BT
adopted multicomponent microturbulent models together with the possibility to
vary freely the local continuum level around each HI line to improve the fit.
The procedure failed, however, to fit adequately D Ly-beta without recourse to
an additional H Ly-alpha contamination at the position of D Ly-beta. We show
that this obstacle may be successfully overcome within the framework of the
mesoturbulent model accounting (in contrast to the microturbulent
approximation) for a correlated structure of the large scale velocity field.
Using the same observational data and the original continuum as determined by
Tytler et al. (1996), we obtained good fits. The one-component mesoturbulent
models provide D/H in the range (3.2 - 4.8) 10^{-5} and the total hydrogen
column density N(HI) = (5.6 - 7.0) 10^{17} cm^{-2}. This result is consistent
with that found by us from the z_a = 2.504 and z_a = 0.701 systems toward
Q1009+2956 and Q1718+4807, respectively. The range for D/H common to all three
analyses is D/H = (4.1 - 4.6) 10^{-5}. This value is consistent with standard
big bang nucleosynthesis [SBBN] if the baryon-to-photon ratio, \eta, is in the
range 4.2 10^{-10} <= \eta <= 4.6 10^{-10}, implying 0.0155 <= \Omega_b
h^2_{100} <= 0.0167.Comment: 8 pages, 2 Postscript figures, aaspp4.sty file, submit. ApJ Let