| 1. |
- Andersson, Martin, et al.
(författare)
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Analysis of the competition between forbidden and hyperfine-induced transitions in Ne-like ions
- 2016
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 93:3
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Tidskriftsartikel (refereegranskat)abstract
- In this work we investigate the decay of the |2p53sP03) state in neon-like ions along the isoelectronic sequence ranging from Z=10 to Z=35. In the absence of a nuclear spin, the magnetic dipole transition to |2p53sP13) is the dominating decay channel. However, for isotopes with a nuclear spin, the interaction between the nuclear magnetic dipole moment and the electronic field introduces a mixing of |2p53sP13) and |P11) into the |P03) state, which in turn opens up a competing hyperfine-induced electric dipole decay channel to the ground state. This hyperfine-induced transition channel clearly dominates over the magnetic dipole channel for the neutral end of the isoelectronic sequence, when present. We give values for the rates of both these competing channels and discuss how the introduction of the hyperfine-induced transition channel could have a dramatic influence on the spectrum, not only because it introduces a new line, but also since it can substantially decrease the intensity of the magnetic dipole 2p53sP03→2p53sP13 line and affect the predicted ionization balance in different plasmas.
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| 2. |
- Andersson, Martin, et al.
(författare)
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HYPERFINE-DEPENDENT gf -VALUES OF Mn i LINES IN THE 1.49–1.80 μm H BAND
- 2015
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Ingår i: The Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 216:1
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Tidskriftsartikel (refereegranskat)abstract
- The three Mn I lines at 17325, 17339, and 17349 angstrom are among the 25 strongest lines (log(gf) > 0.5) in the H band. They are all heavily broadened due to hyperfine structure, and the profiles of these lines have so far not been understood. Earlier studies of these lines even suggested that they were blended. In this work, the profiles of these three infrared (IR) lines have been studied theoretically and compared to experimental spectra to assist in the complete understanding of the solar spectrum in the IR. It is shown that the structure of these lines cannot be described in the conventional way using the diagonal A and B hyperfine interaction constants. The off-diagonal hyperfine interaction not only has a large impact on the energies of the hyperfine levels, but also introduces a large intensity redistribution among the hyperfine lines, changing the line profiles dramatically. By performing large-scale calculations of the diagonal and off-diagonal hyperfine interaction and the gf-values between the upper and lower hyperfine levels and using a semi-empirical fitting procedure, we achieved agreement between our synthetic and experimental spectra. Furthermore, we compare our results with observations of stellar spectra. The spectra of the Sun and the K1.5 III red giant star Arcturus were modeled in the relevant region, 1.73-1.74 mu m, using our theoretically predicted gf-values and energies for each individual hyperfine line. Satisfactory fits were obtained and clear improvements were found using our new data compared with the old available Mn I data. A complete list of energies and gf-values for all the 3d(5)4s(S-7)4d e(6)D - 3d(5)4s(S-7)4f w(6)F hyperfine lines are available as supporting material, whereas only the stronger lines are presented and discussed in detail in this paper.
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| 3. |
- Brage, Tomas, et al.
(författare)
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Resolving a discrepancy between experimental and theoretical lifetimes in atomic negative ions
- 2017
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 50:2
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Tidskriftsartikel (refereegranskat)abstract
- A recent measurement of the lifetime of the excited 3p5 state in the S- negative ion, which is dominated by a forbidden magnetic dipole transition to the 2 P3/ 2 ground state, reveals a discrepancy with earlier theoretical predictions. To investigate this we have performed systematic and large-scale multiconfiguration Dirac-Hartree-Fock calculations for this system. After including a careful treatment of correlation and relativistic effects, we predict a well-converged value for this lifetime, with an uncertainty considerably less than 1%, thereby removing the apparent conflict between theory and experiment. We also show that this result corresponds to the non-relativistic limit in the LS coupling approximation for the magnetic dipole transition within this 2 P term. In addition we demonstrate the usefulness of the latter approach for 2 P transitions in O-, Se- and Te-, as well as for analogous M1 transitions within 2 D terms in Ni- and Pt- ions.
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| 4. |
- Grumer, Jon
(författare)
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Theoretical Atomic Spectroscopy of Earthbound and Stellar Plasma
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Motivated by spectroscopic analysis of astrophysical and laboratory plasma, this thesis concerns the fundamental structure and spectral properties of atoms and their ions. The multiconfiguration Dirac-Hartree-Fock (MCDHF) method is used to predict the emission or absorption of radiation, by atomic systems in general, and of heavy and highly charged ions in particular.The first set of publications, paper AI to AVII, concerns ab-initio predictions of atomic structure and radiative transition rates, with a particular focus on relativistic and electron correlation effects. Systematic and large-scale MCDHF calculations have been carried out, often in combination with electron-beam ion trap experiments.The second set, BI to BVIII, presents a rigorous treatment of effects from non-spherical interactions with certain nuclei - hyperfine interaction - and external magnetic fields - Zeeman interaction - on atomic spectra. A general methodology has been developed and implemented in computer codes to include these perturbations in the wavefunctions and to determine their impact on the resulting spectra. Of particular interest are spectral intensity redistributions and unexpected transitions, and their applications to stellar abundance analyses, magnetic-fields effects in storage-ring experiments, and coronal magnetic-field measurements.
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| 5. |
- Guo, Xueling, et al.
(författare)
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Energy levels and radiative data for Kr-like W38+ from MCDHF and RMBPT calculations
- 2016
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 49:13
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Tidskriftsartikel (refereegranskat)abstract
- Energies, transition rates, line strengths and lifetimes have been computed for all levels of the 4p 6 and 4p 54d configurations of W38+ by using the multi-configuration Dirac-Hartree-Fock (MCDHF) method as well as relativistic many-body perturbation theory. We investigate systematically correlation, relativistic and quantum electro-dynamical (QED) effects of different properties, including excitation energies and transition rates. We demonstrate that it is important to include the core-valence correlation of rather deep subshells (including 3d and 3p) to reach close to spectroscopic accuracy for the transition energies. We also show that high-multipole transitions (E3, M2) are important for the lifetime of some metastable levels of 4p 54d (). The present results are in good agreement with experiments and of considerably higher accuracy than those achieved in previous theoretical works.
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| 6. |
- Li, Wenxian, et al.
(författare)
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A Novel Method to Determine Magnetic Fields in Low-density Plasma Facilitated Through Accidental Degeneracy of Quantum States in Fe9
- 2015
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Ingår i: Astrophysical Journal. - 0004-637X. ; 807:1
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Tidskriftsartikel (refereegranskat)abstract
- We propose a new method to determine magnetic fields, by using the magnetic-field-induced electric dipole transition 3p(4) 3d D-4(7/2) -> 3p(5) P-3/2 in Fe9+ ions. This ion has a high abundance in astrophysical plasma and is therefore well suited for direct measurements of even rather weak fields in, e.g., solar flares. This transition is induced by an external magnetic field and its rate is proportional to the square of the magnetic field strength. We present theoretical values for what we will label the reduced rate and propose that the critical energy difference between the upper level in this transition and the close-to-degenerate 3p(4) 3d D-4(5/2) should be measured experimentally since it is required to determine the relative intensity of this magnetic line for different magnetic fields.
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| 7. |
- Li, Wenxian, et al.
(författare)
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ATOMIC-LEVEL PSEUDO-DEGENERACY of ATOMIC LEVELS GIVING TRANSITIONS INDUCED by MAGNETIC FIELDS, of IMPORTANCE for DETERMINING the FIELD STRENGTHS in the SOLAR CORONA
- 2016
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Ingår i: Astrophysical Journal. - 0004-637X. ; 826:2
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Tidskriftsartikel (refereegranskat)abstract
- We present a measured value for the degree of pseudo-degeneracy between two fine-structure levels in Fe9+ from line intensity ratios involving a transition induced by an external magnetic field. The extracted fine-structure energy difference between 3p4 3d 4D7/2 the and 4D7/2 levels, where the latter is the upper state for the magnetic-field induced line, is needed in our recently proposed method to measure magnetic-field strengths in the solar corona. The intensity of the 3p4 3d 4D7/2 → 3p5 2 P3/2 line at 257.262 Å is sensitive to the magnetic field external to the ion. This sensitivity is in turn strongly dependent on the energy separation in the pseudo-degeneracy through the mixing induced by the external magnetic field. Our measurement, which uses an Electron Beam Ion Trap with a known magnetic-field strength, indicates that this energy difference is 3.5 cm-1. The high abundance of Fe9+ and the sensitivity of the line's transition probability to field strengths below 0.1 T opens up the possibility of diagnosing coronal magnetic fields. We propose a new method to measure the magnetic field in the solar corona, from similar intensity ratios in Fe9+. In addition, the proposed method to use the line ratio of the blended line 3p4 3d 4D7/2.5/2 → 3p5 2P3/2 with another line from Fe x as the density diagnostic should evaluate the effect of the magnetic-field-induced transition line.
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| 8. |
- Wenxian, Li, et al.
(författare)
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A Novel Method to Determine Magnetic Fields in low-density Plasma eg Solar Flares Facilitated Through Accidental Degeneracy of Quantum States in Fe 9
- 2015
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Ingår i: Astrophysical Journal. - : Bibliopolis, Edizioni di Filosofia e Scienze. - 0004-637X .- 1538-4357. ; 807:1
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Tidskriftsartikel (refereegranskat)abstract
- We propose a new method to determine magnetic fields, by using the magnetic-field-induced electric dipole transition 3p4 3d 4D 7 2 3p P 5 2 3 2 in Fe9+ ions. This ion has a high abundance in astrophysical plasma and is therefore well suited for direct measurements of even rather weak fields in, e.g., solar flares. This transition is induced by an external magnetic field and its rate is proportional to the square of the magnetic field strength. We present theoretical values for what we will label the reduced rate and propose that the critical energy difference between the upper level in this transition and the close-to-degenerate 3p4 3d 4D 5 2 should be measured experimentally since it is required to determine the relative intensity of this magnetic line for different magnetic fields.
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