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| 2. |
- Sikstrom, C. M, et al.
(författare)
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New Zr II oscillator strengths and the zirconium conflict in the HgMn star chi Lupi
- 1999
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Ingår i: Astronomy & Astrophysics. - 0004-6361. ; 343:1, s. 297-302
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Tidskriftsartikel (refereegranskat)abstract
- Lifetimes on the sub-nanosecond scale for the levels v(2)D(3/2), v(2)F(3/2) and v(2)F(5/2) in the 4d5s5p configuration in Zr II have been measured, using the method of laser-induced fluorescence. Combined with branching fractions obtained with the Lund Ultraviolet (UV) Fourier Transform Spectrometer (FTS), experimental oscillator strengths have been derived. From Hubble Space Telescope/Goddard High-Resolution Spectrograph spectra, the zirconium abundance in the HgMn star chi Lupi has been determined from Zr II and Zr III lines. More than an order of magnitude difference in the Zr II abundance has been derived from these ionization stages. The difference is much too large to be explained by uncertainties in the oscillator strengths. Possible explanations of this difference have to be found in the stellar models, such as the influence of non-LTE or diffusion.
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| 3. |
- Sikstrom, C. M, et al.
(författare)
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The FERRUM project: experimental lifetimes of highly excited FeII 3d(6)4p levels and transition probabilities
- 1999
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 32:24, s. 5687-5698
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Tidskriftsartikel (refereegranskat)abstract
- We report on measurements of radiative lifetimes in singly ionized iron of six 3d(6)4p levels between 61 512 and 64 041 cm(-1),using time resolved laser-induced fluorescence. Absolute oscillator strengths of 18 Fe II lines in the wavelength range from 2350 to 2800 Angstrom have been obtained by measuring branching fractions for the lines from two Fe II levels with a Fourier-transform spectrometer. The uncertainty in the lifetimes is between 8% and 13%, whereas the uncertainty of the f-values varies between 9% and 19%. A comparison with several previously published values is given.
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| 4. |
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| 5. |
- Li, Z. S, et al.
(författare)
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Lifetime measurements in CeI, CeII, and CeIII using time-resolved laser spectroscopy with application to stellar abundance determinations of cerium
- 2000
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 62:3
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Tidskriftsartikel (refereegranskat)abstract
- Radiative lifetimes of two levels in Ce I, eight levels in Ce rr, and nine levels in Ce III have been measured using the time-resolved laser-induced fluorescence technique. Free cerium atoms and singly and doubly ionized ions were obtained in a laser-produced plasma. A narrow bandwidth UV laser pulse was employed to selectively populate the short-lived upper levels and the lifetime values were evaluated from the time-resolved fluorescence signals recorded by a fast detection system. Transition probabilities for Ce III were obtained from branching fractions calculated by the Cowan code and the experimental lifetimes. The results are compared with previous measurements and calculations. Spectral Lines of Ce III were identified in the spectrum of the magnetic chemically peculiar star alpha(2)CVn and the abundance of cerium was determined from synthetic spectrum fitting to be 800 times greater than the solar abundance.
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| 6. |
- Li, Z. S, et al.
(författare)
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The FERRUM project: radiative lifetimes of intermediate-excitation states of Fe II measured in a fluorescence signal induced by laser pumping from a metastable state
- 1999
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Ingår i: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060. ; 6:1, s. 9-12
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Tidskriftsartikel (refereegranskat)abstract
- A new collaborative program, the FERRUM project. aims at extending and improving the database of oscillator strengths for the astrophysical important Fe II spectrum. In this paper we report on the experimental method applied for measurements of radiative lifetimes of Fe II levels at intermediate excitation (5-10 eV) that can be populated ba laser excitation from metastable states. The technique involves a laser-produced plasma as a source for metastable ions, a stimulated Brillouin scatttering cell for shortening the laser pulse, and fast time resolved detection. We have applied the technique on two Fe II levels at about 7.5 eV and obtained the lifetimes: tau(z(4)S(3/2)(0)) = 3.8(2) ns; tau(y(4)P(5/2)(0)) = 3.6(3) Its.
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| 7. |
- Nilsson, H, et al.
(författare)
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The FERRUM project: new experimental and theoretical f-values for 4p-4d transitions in FeII applied to HST spectra of chi Lupi
- 2000
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Ingår i: Astronomy & Astrophysics. - 0004-6361. ; 362:1, s. 410-418
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Tidskriftsartikel (refereegranskat)abstract
- Radiative lifetimes for six highly excited levels in Fe II have been measured at Lund Laser Centre applying the laser induced fluorescence technique and two-step excitation. The energy levels belong to the even-parity 3d(6)(D-5)(4)d subconfiguration at about 10 eV. Branching fractions (BF:s) of 29 transitions from these levels to the 3d(6)(D-5)4p subconfiguration at about 5 eV have been measured in the wavelength region 2000-3000 Angstrom with the Lund Fourier Transform Spectrometer. By normalizing the BF:s with the lifetimes we get experimental oscillator strengths for these 29 4p-4d lines. The oscillator strengths are compared with new theoretical calculations using the orthogonal operator technique and applied to high-resolution spectra of the star chi Lupi, recorded with the Hubble Space Telescope.
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| 8. |
- Sikstrom, C. M, et al.
(författare)
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Experimental MoII oscillator strengths
- 2001
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 34:3, s. 477-490
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Tidskriftsartikel (refereegranskat)abstract
- Experimental branching fractions (BFs) of Mo (II,) ranging in wavelength from 1970 to 4370 Angstrom, have been measured from intensity calibrated spectra recorded with the Lund UV Fourier transform spectrometer (FTS). Radiative lifetimes for 10 levels have been measured using the method of laser-induced fluorescence (LIF). Combining BFs with new as well as previously measured lifetimes, 16 in total, oscillator strengths of 91 lines were derived. Seven transitions are resonance lines involving the ground state. The BF results are compared with calculations made with the Cowan code and the f-values are compared with previously published data. Improved wavelengths from an ongoing term analysis are also reported.
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