216 research outputs found
Nuclear recoil effect on the magnetic-dipole decay rates of atomic levels
The effect of finite nuclear mass on the magnetic-dipole transition
probabilities between fine-structure levels of the same term is investigated.
Based on a rigorous QED approach a nonrelativistic formula for the recoil
correction to first order in m_e/M is derived. Numerical results for
transitions of experimental interest are presented.Comment: 9 page
Fe VII lines in the spectrum of RR Telescopii
Thirteen transitions within the ground 3d^2 configuration of Fe VII are
identified in ultraviolet and optical spectra of the symbiotic star RR
Telescopii obtained with the STIS instrument of the Hubble Space Telescope. The
line fluxes are compared with theoretical data computed with the recent atomic
data of K.A. Berrington et al., and high resolution optical spectra from
VLT/UVES are used to identify blends. Seven branching ratios are measured, with
three in good agreement with theory and one affected by blending. The
lambda5277/lambda4943 branching ratio is discrepant by > 3 sigma, indicating
errors in the atomic data for the lambda5277 line. A least-squares minimization
scheme is used to simultaneously derive the temperature, T, and density, N_e,
of the RR Tel nebula, and the interstellar extinction, E(B-V), towards RR Tel
from the complete set of emission lines. The derived values are: log T/K = 4.50
+/- 0.23, log N_e/cm^-3=7.25 +/- 0.05, and E(B-V)<0.27. The extinction is not
well-constrained by the Fe VII lines, but is consistent with the more accurate
value E(B-V)=0.109^{+0.052}_{-0.059} derived here from the Ne V
lambda2974/lambda1574 ratio in the STIS spectrum. Large differences between the
K.A. Berrington et al. electron excitation data and the earlier F.P. Keenan &
P.H. Norrington data-set are demonstrated, and the latter is shown to give
worse agreement with observations.Comment: To be published in Astronomy & Astrophysics; 7 pages, 4 figure
Emission lines of Fe XI in the 257--407 A wavelength region observed in solar spectra from EIS/Hinode and SERTS
Theoretical emission-line ratios involving Fe XI transitions in the 257-407 A
wavelength range are derived using fully relativistic calculations of radiative
rates and electron impact excitation cross sections. These are subsequently
compared with both long wavelength channel Extreme-Ultraviolet Imaging
Spectrometer (EIS) spectra from the Hinode satellite (covering 245-291 A), and
first-order observations (235-449 A) obtained by the Solar Extreme-ultraviolet
Research Telescope and Spectrograph (SERTS). The 266.39, 266.60 and 276.36 A
lines of Fe XI are detected in two EIS spectra, confirming earlier
identifications of these features, and 276.36 A is found to provide an electron
density diagnostic when ratioed against the 257.55 A transition. Agreement
between theory and observation is found to be generally good for the SERTS data
sets, with discrepancies normally being due to known line blends, while the
257.55 A feature is detected for the first time in SERTS spectra. The most
useful Fe XI electron density diagnostic is found to be the 308.54/352.67
intensity ratio, which varies by a factor of 8.4 between N_e = 10^8 and 10^11
cm^-3, while showing little temperature sensitivity. However, the 349.04/352.67
ratio potentially provides a superior diagnostic, as it involves lines which
are closer in wavelength, and varies by a factor of 14.7 between N_e = 10^8 and
10^11 cm^-3. Unfortunately, the 349.04 A line is relatively weak, and also
blended with the second-order Fe X 174.52 A feature, unless the first-order
instrument response is enhanced.Comment: 9 pages, 5 figures, 13 tables; MNRAS in pres
Recommended from our members
High-Resolution Laboratory Measurements and Identification of Fe IX Lines near 171 Å
A multitude of weaker Fe IX lines have been predicted in the vicinity of the strong 171 Å line that dominates the spectra of many astrophysical and laboratory sources. Some of these weaker lines have only recently been identified in the laboratory, albeit some only tentatively. Here, we present measurements on the Livermore EBIT-I electron beam ion trap that span the region from 170.0 to 173.6 Å, which surrounds the 171 Å line. The measurements stepped through electron beam energy to determine the charge state of iron associated with each observed feature. Moreover, we have minimized the presence of oxygen in the trap, because oxygen lines obscured possible Fe IX lines in past measurements and prevented their identification. Our measurement confirms formerly tentative identifications and adds several new assignments
QED self-energy contribution to highly-excited atomic states
We present numerical values for the self-energy shifts predicted by QED
(Quantum Electrodynamics) for hydrogenlike ions (nuclear charge ) with an electron in an , 4 or 5 level with high angular momentum
(). Applications include predictions of precision transition
energies and studies of the outer-shell structure of atoms and ions.Comment: 20 pages, 5 figure
Measurement of the Two-Loop Lamb Shift in Lithiumlike U
Using the SuperEBIT electron beam ion trap we have measured the 2s{sub 1/2}-2p{sub 1/2} transitions in U{sup 88+} and U{sup 89+}. The value of 280.645 {+-} 0.015 eV for Li-like U{sup 89+} improves the available precision by nearly an order of magnitude and establishes a new benchmark for testing QED, including higher-order contributions, within a fractional accuracy of better than 3 x 10{sup -4}. From our measurement, we infer a value for both the 2s and 1s two-loop Lamb shift, yielding excellent agreement with recent calculations of the 1.26 eV 1s two-loop Lamb shift in U{sup 91+}
Recommended from our members
Laboratory Search for Fe IX Solar Diagnostic Lines Using an Electron Beam Ion Trap
The Fe IX spectrum features two lines in the extreme ultraviolet whose ratio has been rated among the best density diagnostics in the solar spectrum. One line is an E1-allowed intercombination transition at 244.909 Å, the other an E1-forbidden M2 transition at 241.739 Å. Employing a medium and a high resolution spectrometer at the Livermore EBIT-I electron beam ion trap, we have observed the line pair in the laboratory for the first time. Using a CHIANTI model computation, the observed line ratio yields a value of the electron density that is compatible with typical densities in our device
- …