Transition probabilities of astrophysican interest in the niobium ions (Nb II and Nb III)

in Astronomy and Astrophysics (2010)

Aims. We attempt to derive accurate transition probabilities for astrophysically interesting spectral lines of Nb ii and Nb iii and determine the niobium abundance in the Sun and metal-poor stars rich in ... [more ▼]

Aims. We attempt to derive accurate transition probabilities for astrophysically interesting spectral lines of Nb ii and Nb iii and determine the niobium abundance in the Sun and metal-poor stars rich in neutron-capture elements. Methods. We used the time-resolved laser-induced fluorescence technique to measure radiative lifetimes in Nb ii. Branching fractions were measured from spectra recorded using Fourier transform spectroscopy. The radiative lifetimes and the branching fractions were combined yielding transition probabilities. In addition, we calculated lifetimes and transition probablities in Nb ii and Nb iii using a relativistic Hartree-Fock method that includes core polarization. Abundances of the sun and five metal-poor stars were derived using synthetic spectra calculated with the MOOG code, including hyperfine broadening of the lines. Results. We present laboratory measurements of 17 radiative lifetimes in Nb ii. By combining these lifetimes with branching fractions for lines depopulating the levels, we derive the transition probabilities of 107 Nb ii lines from 4d35p configuration in the wavelength region 2240−4700 Å. For the first time, we present theoretical transition probabilities of 76 Nb III transitions with wavelengths in the range 1430−3140 Å. The derived solar photospheric niobium abundance log = 1.44 ± 0.06 is in agreement with the meteoritic value. The stellar Nb/Eu abundance ratio determined for five metal-poor stars confirms that the r-process is a dominant production method for the n-capture elements in these stars. [less ▲]

HD 65949: Rosetta Stone or Red Herring

in Monthly Notices of the Royal Astronomical Society (2010), 405

HD 65949 is a late B star with exceptionally strong Hg II λ3984, but it is not a typical HgMn star. The Re II spectrum is of extraordinary strength. Abundances or upper limits are derived here for 58 ... [more ▼]

HD 65949 is a late B star with exceptionally strong Hg II λ3984, but it is not a typical HgMn star. The Re II spectrum is of extraordinary strength. Abundances or upper limits are derived here for 58 elements based on a model with Teff = 13 100K and log(g) = 4.0. Even-Z elements through nickel show minor deviations from solar abundances. Anomalies among the odd-Z elements through copper are mostly small. Beyond the iron peak, a huge scatter is found. Enormous enhancements are found for the elements rhenium through mercury (Z = 75–80). We note the presence of Th III in the spectrum. The abundance pattern of the heaviest elements resembles the N = 126 r-process peak of solar material, though not in detail. An odd-Z anomaly appears at the triplet (Zr Nb Mo), and there is a large abundance jump between Xe (Z = 54) and Ba (Z = 56). These are signatures of chemical fractionation. We find a significant correlation of the abundance excesses with second ionization potentials for elements withZ > 30. If this is not a red herring (false lead), it indicates the relevance of photospheric or near-photospheric processes. Large excesses (4–6 dex) require diffusion from deeper layers with the elements passing through a number of ionization stages. That would make the correlation with second ionization potential puzzling. We explore a model with mass accretion of exotic material followed by the more commonly accepted differentiation by diffusion. That model leads to a number of predictions which challenge future work. New observations confirm the orbital elements of Gieseking and Karimie, apart from the systemic velocity, which has increased. Likely primary and secondary masses are near 3.3 and 1.6 M , with a separation of ca. 0.25 au. New atomic structure calculations are presented in two appendices. These include partition functions for the first through third spectra of Ru, Re and Os, as well as oscillator strengths in the Re II spectrum. [less ▲]

Experimental and theoretical radiative decay rates for highly excited ruthenium atomic levels and the solar abundance of ruthenium

in Monthly Notices of the Royal Astronomical Society (2009), 396

The solar photospheric abundance of ruthenium is revised on the basis of a new set of oscillator strengths derived for Ru I transitions with wavelengths in the spectral range 2250–4710 Å. The new ... [more ▼]

The solar photospheric abundance of ruthenium is revised on the basis of a new set of oscillator strengths derived for Ru I transitions with wavelengths in the spectral range 2250–4710 Å. The new abundance value (in the usual logarithmic scale where the solar hydrogen abundance is equal to 12.00), ARu = 1.72 ± 0.10, is in agreement with the most recent meteoritic result, ARu = 1.76 ± 0.03. The accuracy of the transition probabilities, obtained using a relativistic Hartree–Fock model including core-polarization effects, has been assessed by comparing the theoretical lifetimes with previous experimental results. A comparison is also made with new measurements performed in this work by the time-resolved laser-induced fluorescence spectroscopy for 10 highly excited odd-parity levels of Ru I [less ▲]

Lifetime measurements and calculated transition probabilities in WIII

in Physica Scripta (2008), 78

New experimental lifetimes for two levels in doubly ionized tungsten, W III, have been obtained using the time-resolved laser-induced-fluorescence technique. Theoretical oscillator strengths obtained from ... [more ▼]

New experimental lifetimes for two levels in doubly ionized tungsten, W III, have been obtained using the time-resolved laser-induced-fluorescence technique. Theoretical oscillator strengths obtained from a HFR calculation including the effects of core-polarization are reported for all transitions from levels below E < 70 000 cm−1 and with log g f > −2, thus greatly extending our knowledge of the radiative data in W III. Good agreement is found between the calculated lifetimes and the experimental values from this and previous works. These new results fill a gap in the available data for this ion which is expected to play an important role in fusion reactors. [less ▲]

Lifetimes of metastable levels of singly ionized titanium: theory and experiment

in Journal of Physics : B Atomic Molecular & Optical Physics (2008), 41

This paper presents new theoretical lifetimes of metastable levels in singly ionized titanium, Ti II. Along with the lifetimes, transition probabilities for several decay channels from these metastable ... [more ▼]

This paper presents new theoretical lifetimes of metastable levels in singly ionized titanium, Ti II. Along with the lifetimes, transition probabilities for several decay channels from these metastable levels are presented. The calculations are supported by experimental lifetime determinations of the 3d3 b 2D5/2 and 3d2(3P)4s b 2P3/2 levels along with revised values of the previously published lifetimes of the 3d2(3P)4s b 4P5/2 and 3d2(3P)4s b 2P1/2 levels originating partly from a reanalysis utilizing a recently developed method applied on the previously recorded data and partly from new measurements. The presented theoretical investigation of lifetimes of metastable levels in Ti II shows that the HFR calculations are in general compatible with measurements performed using the ion storage ring CRYRING of Stockholm University. The transition probabilities of forbidden lines derived from the new lifetime values will be useful for the diagnostics of low density laboratory or astrophysical plasmas, particularly those encountered in the strontium filament found in the ejecta of η Carinae. [less ▲]

Laser-induced-fluorescence lifetime measurements and relativistic Hartree-Fock oscillator strength calculations in singly ionized platinum

in Physical Review. A (2008), 77

Radiative lifetimes of eight odd-parity states of Pt II, in the energy range from 51 408 to 64 388 cm−1, have been measured by means of the time-resolved laser-induced-fluorescence technique. Free, singly ... [more ▼]

Radiative lifetimes of eight odd-parity states of Pt II, in the energy range from 51 408 to 64 388 cm−1, have been measured by means of the time-resolved laser-induced-fluorescence technique. Free, singly ionized platinum ions were obtained in a laser-produced plasma and a tunable laser with 1.5 ns duration pulse was used to selectively excite the Pt+ ions. The comparison of the experimental results with relativistic Hartree-Fock calculations emphasizes the importance of valence-valence correlation and of core-polarization effects in this complex ion. A new and extensive set of calculated oscillator strengths and transition probabilities is reported in the present paper. [less ▲]

Relativistic atomic data for EUV and X-ray lines in the highly charged Zn-like ions from Yb40+ to U62+

in Atomic Data and Nuclear Data Tables (2007), 93(5), 711-729

The wavelengths and transition probabilities for EUV and X-ray lines in the spectra from Yb XLI to U LXIII along the zinc isoelectronic sequence have been calculated using a multiconfiguration Dirac-Fock ... [more ▼]

The wavelengths and transition probabilities for EUV and X-ray lines in the spectra from Yb XLI to U LXIII along the zinc isoelectronic sequence have been calculated using a multiconfiguration Dirac-Fock (MCDF) model. Results are reported for the 4S(2) -4s4p, 4s4p-4p(2), and 4s4p-4s4d transitions. A comparison of the calculated wavelengths with the few experimental results available is also presented. (c) 2007 Elsevier Inc. All rights reserved. [less ▲]

Radiative decay from the 7s(1/2) level in Pb+ and transition probabilities of astrophysical interest in Pb+ and Bi++

in Journal of Physics B-Atomic Molecular and Optical Physics (2007), 40(10), 1705-1712

In the present work, we report on experimental and theoretical determination of the decay rates from the 7s(1)/2 state in singly ionized lead. Lifetime measurements performed using time-resolved laser ... [more ▼]

In the present work, we report on experimental and theoretical determination of the decay rates from the 7s(1)/2 state in singly ionized lead. Lifetime measurements performed using time-resolved laser-induced fluorescence spectroscopy and lifetime computations carried out with themulticonfiguration Dirac-Fock method allow us to solve the discrepancies previously observed between theory and experiment for this level. New transition probabilities are proposed for the two depopulation channels, i. e. the 6p(1/2-7s1/2) and 6p(3/2-7s1/2) transitions of astrophysical interest in Pb II and Bi III, respectively. [less ▲]

Transition probabilities and lifetimes for atoms and ions from the sixth row of the periodic table and the database DESIRE

in Journal of Electron Spectroscopy and Related Phenomena (2007), 156

We have started a systematic investigation of the radiative properties of the elements of the sixth row of the periodic table. Using a combination of experimental radiative lifetimes obtained with the ... [more ▼]

We have started a systematic investigation of the radiative properties of the elements of the sixth row of the periodic table. Using a combination of experimental radiative lifetimes obtained with the time-resolved laser-induced fluorescence (LIF) technique and of theoretical branching fractions (BF) calculated with a HFR approach taking configuration interaction and core-polarization effects into account, transition probabilities have been deduced for a number of transitions of astrophysical interest. So far results have been obtained for the elements Ta, Re, Os, Ir, Tl or An or their ions. The results obtained are stored in the database DatabasE for the SIxth Row Elements (DESIRE), an extension of the database DREAM, which will be progressively created on a web site of the University of Mons-Hainaut in Belgium. In the present paper, some emphasis is put on the procedures followed to obtain the new results but also on the difficulties associated with their determination. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Improved atomic data for iridium atom (Ir I) and ion (Ir II) and the solar content of iridium

in Journal of Quantitative Spectroscopy & Radiative Transfer (2007), 104(1), 52-70

From a combination of radiative lifetime measurements, performed with a time-resolved laser-induced fluorescence technique, for nine odd-parity levels of Ir I and four odd-parity levels of Ir 11 and ... [more ▼]

From a combination of radiative lifetime measurements, performed with a time-resolved laser-induced fluorescence technique, for nine odd-parity levels of Ir I and four odd-parity levels of Ir 11 and branching fraction calculations, extended sets of transition probabilities have been derived for transitions of astrophysical interest. The new results are compared with the few experimental data available in the literature and a good agreement is found. They extend considerably the previous sets of transition probabilities available in the literature. Implications of the new results regarding the solar content of iridium are briefly discussed. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]