52 research outputs found
MCDHF calculations of isotope shifts in neutral antimony
Ab initio multiconfiguration Dirac–Hartree–Fock (MCDHF) calculations have been carried out in order to determine the isotope shift (IS) electronic parameters of transitions belonging to electric dipole (E1) transition arrays 5s25p3−5s25p26s, 5s25p26s−5s25p26p and 5s25p26s−5s25p27p in neutral antimony, Sb I. In a correlation model limited to single and double excitations from the valence shells, these parameters, combined with the changes in mean-square nuclear charge radius δ⟨r2⟩123,121 compiled by Angeli and Marinova [3] produce isotope shifts values in good agreement with the most recent measurements by high-resolution emission and optogalvanic absorption spectroscopy of Sobolewski et al. [5] but not with the old measurements of Buchholz et al. [4] for 5p3−5p26s. However, our analysis does not allow to reject the latter due to the large uncertainty affecting δ⟨r2⟩123,121, i.e. 0.072 ± 0.048 fm2 [3]. This shows the need of a more accurate determination of this nuclear parameter. Although improving excitation energies, the inclusion of core-valence correlation limited to one hole in the 4d core subshell destroyed the theory-experiment agreement on the IS parameters. © 2018 Elsevier LtdInteruniversity Attraction Poles Programm
Stellar laboratories. VIII. New Zr IV - VII, Xe IV - V, and Xe VII oscillator strengths and the Al, Zr, and Xe abundances in the hot white dwarfs G191-B2B and RE0503-289
For the spectral analysis of high-resolution and high-signal-to-noise spectra
of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model
atmospheres are mandatory. These are strongly dependent on the reliability of
the atomic data that is used for their calculation.
To search for Zr and Xe lines in the ultraviolet (UV) spectra of G191-B2B and
RE0503-289, new Zr IV-VII, Xe IV-V, and Xe VIII oscillator strengths were
calculated. This allows for the first time, determination of the Zr abundance
in white dwarf (WD) stars and improvement of the Xe abundance determinations.
We calculated Zr IV-VII, Xe IV-V, and Xe VIII oscillator strengths to
consider radiative and collisional bound-bound transitions of Zr and Xe in our
NLTE stellar-atmosphere models for the analysis of their lines exhibited in UV
observations of the hot WDs G191-B2B and RE0503-289.
We identified one new Zr IV, 14 new Zr V, and ten new Zr VI lines in the
spectrum of RE0503-289. Zr was detected for the first time in a WD. We measured
a Zr abundance of -3.5 +/- 0.2 (logarithmic mass fraction, approx. 11 500 times
solar). We dentified five new Xe VI lines and determined a Xe abundance of -3.9
+/- 0.2 (approx. 7500 times solar). We determined a preliminary photospheric Al
abundance of -4.3 +/- 0.2 (solar) in RE0503-289. In the spectra of G191-B2B, no
Zr line was identified. The strongest Zr IV line (1598.948 A) in our model gave
an upper limit of -5.6 +/- 0.3 which is about 100 times solar. No Xe line was
identified in the UV spectrum of G191-B2B and we confirmed the previously
determined upper limit of -6.8 +/- 0.3 (ten times solar).
Precise measurements and calculations of atomic data are a prerequisite for
advanced NLTE stellar-atmosphere modeling. Observed Zr IV - VI and Xe VI - VII
line profiles in the UV spectrum of RE0503-289 were simultaneously well
reproduced.Comment: 137 pages, 11 figure
Experimental and theoretical radiative parameters of highly excited odd-parity levels in Ir II
peer reviewe
Experimental and Theoretical Radiative Lifetimes, Branching Fractions, Transition Probabilities, and Oscillator Strengths of Some Highly Excited Odd-parity Levels in Ir I
Radiative lifetimes of 62 odd-parity levels of Ir i in the energy range between 32513.43 and 58625.10 cm-1 were measured using the time-resolved laser-induced fluorescence technique. The lifetime values obtained are in the range from 3.2 to 345 ns. To our best knowledge, 59 results are reported for the first time. These are compared to computed data deduced from a pseudo-relativistic Hartree-Fock model including core-polarization contributions. From the combination of the experimental lifetime measurements and branching fraction calculations, a new set of transition probabilities and oscillator strengths is derived for 134 Ir i spectral lines of astrophysical interest in the wavelength region from 205 to 418 nm. © 2018. The American Astronomical Society. All rights reserved
First discovery of trans-iron elements in a DAO-type white dwarf (BD)
We have identified 484 lines of the trans-iron elements (TIEs) Zn, Ga, Ge,
Se, Br, Kr, Sr, Zr, Mo, In, Te, I, Xe, and Ba, for the first time in the
ultraviolet spectrum of a DAO-type WD, namely BD, surrounded
by the ionized nebula Abell 35. Our TIE abundance determination shows extremely
high overabundances of up to five dex -- a similar effect is already known from
hot, H-deficient (DO-type) white dwarfs. In contrast to these where a
pulse-driven convection zone has enriched the photosphere with TIEs during a
final thermal pulse and radiative levitation has established the extreme TIE
overabundances, {here the extreme TIE overabundances are exclusively driven by
radiative levitation on the initial stellar metallicity. The very low mass
() of BD implies that a
third dredge-up with enrichment of s-process elements in the photosphere did
not occur in the AGB precursor.Comment: 34 pages, 19 Figure
Branching on multi-aggregated variables
open5siopenGamrath, Gerald; Melchiori, Anna; Berthold, Timo; Gleixner, Ambros M.; Salvagnin, DomenicoGamrath, Gerald; Melchiori, Anna; Berthold, Timo; Gleixner, Ambros M.; Salvagnin, Domenic
Verifying integer programming results
Software for mixed-integer linear programming can return incorrect results for a number of reasons, one being the use of inexact floating-point arithmetic. Even solvers that employ exact arithmetic may suffer from programming or algorithmic errors, motivating the desire for a way to produce independently verifiable certificates of claimed results. Due to the complex nature of state-of-the-art MIP solution algorithms, the ideal form of such a certificate is not entirely clear. This paper proposes such a certificate format designed with simplicity in mind, which is composed of a list of statements that can be sequentially verified using a limited number of inference rules. We present a supplementary verification tool for compressing and checking these certificates independently of how they were created. We report computational results on a selection of MIP instances from the literature. To this end, we have extended the exact rational version of the MIP solver SCIP to produce such certificates
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