60 research outputs found
Probing the time-variation of the fine-structure constant: Results based on Si IV doublets from a UVES sample
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 \Delta\alpha/\alpha = (+0.15+/-0.43) x 10^-5 over a redshift range of
1.59< z < 2.92 which is consistent with no variation in \alpha. This result
represents a factor of three improvement on the constraint on
\Delta\alpha/\alpha based on Si IV doublets compared to the published results
in the literature. The alkali doublet method used here avoids the implicit
assumptions used in the many-multiplet method that chemical and ionization
inhomogeneities are negligible and isotopic abundances are close to the
terrestrial value.Comment: 12 Pages, 7 figures. Accepted for publication in A&A. In addition to
minor corrections an appendix is added in this revised versio
Probing the cosmological variation of the fine-structure constant: Results based on VLT-UVES sample
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. Here we present the results from a detailed many-multiplet analysis
performed using high signal-to-noise ratio, high spectral resolution
observations of 23 Mg II systems detected toward 18 QSOs in the redshift range
0.4<z<2.3 obtained using UVES at the VLT. We validate our procedure and define
the selection criteria that will avoid possible systematics using detail
analysis of simulated data set. We show our Voigt profile fitting code recovers
the variation in \alpha very accurately when we use single component systems
and multiple component systems that are not heavily blended. Spurious
detections are frequently seen when we use heavily blended systems or the
systems with very weak lines. Thus we avoided heavily blended systems and the
systems with Fe II column density < 2x10^12 cm^-2 in the analysis. All steps
involved in the analysis are presented in detail. The weighted mean value of
the variation in \alpha obtained from our analysis over the redshift range
0.4<z<2.3 is {\Delta\alpha/\alpha} = (-0.06+/-0.06)x10^-5. The median redshift
of our sample is 1.55 the 3\sigma upper limit on the time variation of
is -2.5x10^-16 yr^-1< (\Delta\alpha/\alpha\Delta t) <+1.2x10^-16 yr^-1. To our
knowledge this is the strongest constraint from quasar absorption line studies
till date.Comment: 23 pages; A&A style, 15 figures, accepte
Infrared Computer-Generated Holograms: Design and Application for the WFIRST Grism Using Wavelength-Tuning Interferometry
Interferometers using computer-generated holograms (CGHs) have become the industry standard to accurately measure aspheric optics. The CGH is a diffractive optical element that can create a phase or amplitude distribution and can be manufactured with low uncertainty using modern lithographic techniques. However, these CGHs have conventionally been used with visible light and piezo-shifting interferometers. Testing the performance of transmissive optics in the infrared requires infrared CGHs and an infrared interferometer. Such an instrument is used in this investigation, which introduces its phase shift via wavelength-tuning. A procedure on how to design and manufacture infrared CGHs and how these were successfully used to model and measure the Wide-Field Infrared Survey Telescope grism elements is provided. Additionally, the paper provides a parametric model, simulation results, and calculations of the errors and measurements that come about when interferometers introduce a phase variation via wavelength-tuning interferometry to measure precision aspheres
Super-Radiant Dynamics, Doorways, and Resonances in Nuclei and Other Open Mesoscopic Systems
The phenomenon of super-radiance (Dicke effect, coherent spontaneous
radiation by a gas of atoms coupled through the common radiation field) is well
known in quantum optics. The review discusses similar physics that emerges in
open and marginally stable quantum many-body systems. In the presence of open
decay channels, the intrinsic states are coupled through the continuum. At
sufficiently strong continuum coupling, the spectrum of resonances undergoes
the restructuring with segregation of very broad super-radiant states and
trapping of remaining long-lived compound states. The appropriate formalism
describing this phenomenon is based on the Feshbach projection method and
effective non-Hermitian Hamiltonian. A broader generalization is related to the
idea of doorway states connecting quantum states of different structure. The
method is explained in detail and the examples of applications are given to
nuclear, atomic and particle physics. The interrelation of the collective
dynamics through continuum and possible intrinsic many-body chaos is studied,
including universal mesoscopic conductance fluctuations. The theory serves as a
natural framework for general description of a quantum signal transmission
through an open mesoscopic system.Comment: 85 pages, 10 figure
Atomic transition frequencies, isotope shifts, and sensitivity to variation of the fine structure constant for studies of quasar absorption spectra
Theories unifying gravity with other interactions suggest spatial and
temporal variation of fundamental "constants" in the Universe. A change in the
fine structure constant, alpha, could be detected via shifts in the frequencies
of atomic transitions in quasar absorption systems. Recent studies using 140
absorption systems from the Keck telescope and 153 from the Very Large
Telescope, suggest that alpha varies spatially. That is, in one direction on
the sky alpha seems to have been smaller at the time of absorption, while in
the opposite direction it seems to have been larger.
To continue this study we need accurate laboratory measurements of atomic
transition frequencies. The aim of this paper is to provide a compilation of
transitions of importance to the search for alpha variation. They are E1
transitions to the ground state in several different atoms and ions, with
wavelengths ranging from around 900 - 6000 A, and require an accuracy of better
than 10^{-4} A. We discuss isotope shift measurements that are needed in order
to resolve systematic effects in the study. The coefficients of sensitivity to
alpha-variation (q) are also presented.Comment: Includes updated version of the "alpha line" lis
On the variation of the fine-structure constant: Very high resolution spectrum of QSO HE 0515-4414
We present a detailed analysis of a very high resolution (R\approx 112,000)
spectrum of the quasar HE 0515-4414 obtained using the High Accuracy Radial
velocity Planet Searcher (HARPS) mounted on the ESO 3.6 m telescope at the La
Silla observatory. The HARPS spectrum, of very high wavelength calibration
accuracy (better than 1 m\AA), is used to search for possible systematic
inaccuracies in the wavelength calibration of the UV Echelle Spectrograph
(UVES) mounted on the ESO Very Large Telescope (VLT). We have carried out
cross-correlation analysis between the Th-Ar lamp spectra obtained with HARPS
and UVES. The shift between the two spectra has a dispersion around zero of
\sigma\simeq 1 m\AA. This is well within the wavelength calibration accuracy of
UVES (i.e \sigma\simeq 4 m\AA). We show that the uncertainties in the
wavelength calibration induce an error of about, \Delta\alpha/\alpha\le
10^{-6}, in the determination of the variation of the fine-structure constant.
Thus, the results of non-evolving \Delta\alpha/\alpha reported in the
literature based on UVES/VLT data should not be heavily influenced by problems
related to wavelength calibration uncertainties. Our higher resolution spectrum
of the z_{abs}=1.1508 damped Lyman-\alpha system toward HE 0515-4414 reveals
more components compared to the UVES spectrum. Using the Voigt profile
decomposition that simultaneously fits the high resolution HARPS data and the
higher signal-to-noise ratio UVES data, we obtain,
\Delta\alpha/\alpha=(0.05\pm0.24)x10^{-5} at z_{abs}=1.1508. This result is
consistent with the earlier measurement for this system using the UVES spectrum
alone.Comment: 14 pages, 13 figures, Accepted in A&
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