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  • 1.
    Andersson, Martin
    et al.
    Shanghai EBIT Laboratory, Institute of Modern Physics, Fudan University, Shanghai, People's Republic of China; The Key Laboratory of Applied Ion Beam Physics, Ministry of Education, People's Republic of China.
    Lennartsson, Thomas
    Department of Astronomy, Lund University, Sweden.
    Nilsson, Hampus
    Department of Astronomy, Lund University, Sweden.
    Chen, Chongyang
    Shanghai EBIT Laboratory, Institute of Modern Physics, Fudan University, Shanghai, People's Republic of China 2 The Key Laboratory of Applied Ion Beam Physics, Ministry of Education, People's Republic of China.
    The anomalous hyperfine structure of Al II2012In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 45, no 13, p. 135001-135001Article in journal (Refereed)
    Abstract [en]

    The hyperfine structure of a large number of transitions in Al II cannot be described using A and B hyperfine constants and the hyperfine structure is therefore said to be anomalous. In this paper, we have studied the hyperfine structure of a few transitions in Al II, 3s5s3S–3s5p3P, 3s4d3D–3s5p3P and 3s5p3P–3s5d3D, by combining theory and experiment. It is shown that the anomalous hyperfine structure is due to strong off-diagonal hyperfine interaction resulting not only in a deplacement of the energies of the hyperfine levels, but also resulting in large intensity redistribution among the individual hyperfine lines. It is shown that the hyperfine mixing in 3s4d3D and 3s5d3D is very large, whereas small but not negligible in 3s5p3P. By combining experimental spectra and theory we could obtain accurate wavefunctions for the 3s4d3D and 3s5d3D hyperfine levels which were used to calculate the gf-values of all individual hyperfine transitions not only for 3s5p3P, but also for 3s3p3P and 3s4p3P, where the off-diagonal hyperfine interaction leads to negligible intensity redistribution.

  • 2.
    Bean, Jacob L.
    et al.
    Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen.
    Seifahrt, Andreas
    Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen; Department of Physics, University of California, One Shields Avenue, Davis, CA 95616, USA.
    Hartman, Henrik
    Lund Observatory, Lund University, P.O. Box 43, 22100 Lund, Sweden.
    Nilsson, Hampus
    Lund Observatory, Lund University, P.O. Box 43, 22100 Lund, Sweden.
    Reiners, Ansgar
    Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen.
    Dreizler, Stefan
    Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen.
    Henry, Todd J.
    Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302, USA.
    Wiedemann, Günter
    Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany.
    The proposed giant planet orbiting VB 10 does not exist2010In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 711, no 1, p. L19-L23Article in journal (Refereed)
    Abstract [en]

    We present high-precision relative radial velocities of the very low mass star VB 10 that were obtained over a time span of 0.61 years as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the Very Large Telescope with an ammonia gas cell. The typical internal precision of the measurements is 10 m s−1. These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo & Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the ∼1 km s−1 radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with Mp > 3 MJup and the orbital period and inclination suggested by Pravdo & Shaklan at better than 5σ confidence. We conclude that the planet detection claimed by Pravdo & Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low mass stars.

  • 3.
    Bean, Jacob L.
    et al.
    Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen.
    Seifahrt, Andreas
    Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen; Department of Physics, University of California, One Shields Avenue, Davis, CA 95616, USA.
    Hartman, Henrik
    Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Nilsson, Hampus
    Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Wiedemann, Günter
    Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany.
    Reiners, Ansgar
    Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen.
    Dreizler, Stefan
    Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen.
    Henry, Todd J.
    Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302, USA.
    The crires search for planets around the lowest-mass stars. I. High-precision near-infrared radial velocities with an ammonia gas cell2010In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 713, no 1, p. 410-422Article in journal (Refereed)
    Abstract [en]

    Radial velocities measured from near-infrared (NIR) spectra are a potentially powerful tool to search for planets around cool stars and sub-stellar objects. However, no technique currently exists that yields NIR radial velocity precision comparable to that routinely obtained in the visible. We are carrying out an NIR radial velocity planet search program targeting a sample of the lowest-mass M dwarfs using the CRIRES instrument on the Very Large Telescope. In this first paper in a planned series about the project, we describe a method for measuring high-precision relative radial velocities of these stars from K-band spectra. The method makes use of a glass cell filled with ammonia gas to calibrate the spectrograph response similar to the "iodine cell" technique that has been used very successfully in the visible. Stellar spectra are obtained through the ammonia cell and modeled as the product of a Doppler-shifted template spectrum of the object and a spectrum of the cell, convolved with a variable instrumental profile (IP) model. A complicating factor is that a significant number of telluric absorption lines are present in the spectral regions containing useful stellar and ammonia lines. The telluric lines are modeled simultaneously as well using spectrum synthesis with a time-resolved model of the atmosphere over the observatory. The free parameters in the complete model are the wavelength scale of the spectrum, the IP, adjustments to the water and methane abundances in the atmospheric model, telluric spectrum Doppler shift, and stellar Doppler shift. Tests of the method based on the analysis of hundreds of spectra obtained for late-M dwarfs over 6 months demonstrate that precisions of ∼ 5 m s−1 are obtainable over long timescales, and precisions of better than 3 m s−1 can be obtained over timescales up to a week. The obtained precision is comparable to the predicted photon-limited errors, but primarily limited over long timescales by the imperfect modeling of the telluric lines.

  • 4.
    Biémont, É.
    et al.
    Astrophysique et Spectroscopie, Université de Mons - UMONS, B-7000 Mons, 20 Place du Parc, Belgium; IPNAS (Bât. B 15), Université de Liège, Sart-Tilman, B-4000 Liège 1, Belgium.
    Blagoev, K.
    Institute of Solid State Physics, Bulgarian Academy of Sciences, Chaussee, BG-1784 Sofia, 72 Tzarigradsko, Bulgaria.
    Engström, L.
    Department of Physics, Lund University, S-221 00 Lund, PO Box 118, Sweden.
    Hartman, H.
    Lund Observatory, Lund University, S-221 00 Lund, PO Box 43, Sweden.
    Lundberg, H.
    Department of Physics, Lund University, S-221 00 Lund, PO Box 118, Sweden.
    Malcheva, G.
    Institute of Solid State Physics, Bulgarian Academy of Sciences, Chaussee, BG-1784 Sofia, 72 Tzarigradsko, Bulgaria.
    Nilsson, H.
    Lund Observatory, Lund University, S-221 00 Lund, PO Box 43, Sweden.
    Whitehead, R. Blackwell
    Lund Observatory, Lund University, S-221 00 Lund, PO Box 43, Sweden.
    Palmeri, P.
    Astrophysique et Spectroscopie, Université de Mons - UMONS, B-7000 Mons, 20 Place du Parc, Belgium.
    Quinet, P.
    Astrophysique et Spectroscopie, Université de Mons - UMONS, B-7000 Mons, 20 Place du Parc, Belgium; IPNAS (Bât. B 15), Université de Liège, Sart-Tilman, B-4000 Liège 1, Belgium.
    Lifetime measurements and calculations in Y+ and Y2+ ions2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 414, no 4, p. 3350-3359Article in journal (Refereed)
    Abstract [en]

    We report a new set oftheoretical transition probabilities in Yii, obtained using a multiconfiguration relativistic Hartree-Fock method including core polarization. The overall quality of the calculations is assessed by comparisons with new and previous lifetime measurements. In this paper, we report new measurements of five lifetimes in the 4d5p and 5s5p configurations, in the energy range of 32048-44569 cm-1, obtained by the time-resolved laser-induced fluorescence method. A similar theoretical model, applied to Yiii, leads to results in good agreement with new laser measurements of two 5p levels obtained in this work and with previous beam-foil results for 5d and 6s levels. An extensive set of oscillator strengths is also proposed for Yiii.

  • 5.
    Blackwell-Whitehead, R.
    et al.
    Lund Observatory, Box 43, 221 00 Lund, Sweden; Blackett Laboratory, Imperial College London, London SW7 2AZ, UK.
    Pavlenko, Y. V.
    Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK; Main Astronomical Observatory of the Academy of Sciences of Ukraine, Zabolotnoho 27, Kyiv 03680, Ukraine.
    Nave, G.
    Atomic Physics Division, National Institute of Standards and Technology, 100 Bureau Dr., Gaithersburg, MD 20899, USA.
    Pickering, J. C.
    Blackett Laboratory, Imperial College London, London SW7 2AZ, UK.
    Jones, H. R. A.
    Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK.
    Lyubchik, Y.
    Main Astronomical Observatory of the Academy of Sciences of Ukraine, Zabolotnoho 27, Kyiv 03680, Ukraine.
    Nilsson, Hampus
    Lund Observatory, Box 43, 221 00 Lund, Sweden.
    Infrared Mn i laboratory oscillator strengths for the study of late type stars and ultracool dwarfs2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 525, p. A44-A44Article in journal (Refereed)
    Abstract [en]

    Aims. The aim of our new laboratory measurements is to measure accurate absolute oscillator strengths for neutral manganese transitions in the infrared needed for the study of late-type stars and ultracool dwarfs.

    Methods. Branching fractions have been measured by high resolution Fourier transform spectroscopy and combined with radiative level lifetimes in the literature to yield oscillator strengths.

    Results. We present experimental oscillator strengths for 20 Mn I transitions in the wavelength range 3216 to 13 997 Å, 15 of which are in the infrared. The transitions at 12 899 Å and 12 975 Å are observed as strong features in the spectra of late-type stars and ultracool dwarfs. We have fitted our calculated spectra to the observed Mn I lines in spectra of late-type stars. Using the new experimentally measured Mn I log (gf) values together with existing data for Mn I hyperfine structure splitting factors we determined the manganese abundance to be log N(Mn) = −6.65 ± 0.05 in the atmosphere of the Sun, log N(Mn) = 6.95 ± 0.20 in the atmosphere of Arcturus, and log N(Mn) = −6.70 ± 0.20 in the atmosphere of M 9.5 dwarf 2MASSW 0140026+270150.

  • 6.
    Brandt, J. C.
    et al.
    Lab. for Atmosph. and Space Physics, Campus Box 392, University of Colorado, Boulder, CO 80309-0392, United States.
    Heap, S. R.
    Lab. for Astronomy and Solar Physics, Goddard Space Flight Center, Code 681, Greenbelt, MD 20771, United States.
    Beaver, E. A.
    Lab. for Astronomy and Solar Physics, Goddard Space Flight Center, Code 681, Greenbelt, MD 20771, United States.
    Boggess, A.
    Boulder, CO 80304, 2420 Balsam Drive, United States.
    Carpenter, K. G.
    Lab. for Astronomy and Solar Physics, Goddard Space Flight Center, Code 681, Greenbelt, MD 20771, United States.
    Ebbets, D. C.
    Ball Aerosp. and Technol. Corp., AR1, Boulder, CO 80306, P.O. Box 1062, United States.
    Hutchings, J. B.
    Dominion Astrophysical Observatory, Victoria, BC V8X 4M6, 5071 West Saanich Road, Canada.
    Jura, M.
    Department of Physics and Astronomy, Univ. of California, Los Angeles, Los Angeles, CA 90095-1562, United States.
    Leckrone, D. S.
    Lab. for Astronomy and Solar Physics, Goddard Space Flight Center, Code 681, Greenbelt, MD 20771, United States.
    Linsky, J. L.
    JILA, University of Colorado, Natl. Inst. Standards and Technology, Boulder, CO 80309-0440, United States.
    Maran, S. P.
    JILA, University of Colorado, Natl. Inst. Standards and Technology, Boulder, CO 80309-0440, United States.
    Savage, B. D.
    Department of Astronomy, University of Wisconsin, Madison, WI 53706, 475 North Charter Street, United States.
    Smith, A. M.
    Lab. for Astronomy and Solar Physics, Goddard Space Flight Center, Code 681, Greenbelt, MD 20771, United States.
    Trafton, L. M.
    MacDonald Observ. and Astron. Dept., University of Texas, Austin, TX 78712, United State.
    Walter, F. M.
    Astronomy Program, Dept. of Earth and Space Sciences, Stt. Univ. New York at Stony Brook, Stony Brook, NY 11794-2100, United States.
    Weymann, R. J.
    Observatories Carnegie Inst. W., Pasadena, CA 91101, 813 Santa Barbara Street, United States.
    Proffitt, C. R.
    Science Programs, Computer Sciences Corporation, Goddard Space Flight Center, Greenbelt, MD 20771, United States.
    Wahlgren, G. M.
    Science Programs, Computer Sciences Corporation, Goddard Space Flight Center, Greenbelt, MD 20771, United States.
    Johansson, S. G.
    Department of Physics, University of Lund, Box 118, S-22100 Lund, Sweden.
    Nilsson, H.
    Department of Physics, University of Lund, Box 118, S-22100 Lund, Sweden.
    Brage, T.
    Department of Physics, University of Lund, Box 118, S-22100 Lund, Sweden.
    Snow, M.
    Lab. for Atmosph. and Space Physics, Campus Box 392, University of Colorado, Boulder, CO 80309-0392, United States.
    Ake, T. B.
    Science Programs, Computer Sciences Corporation, Goddard Space Flight Center, Greenbelt, MD 20771, United States; Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, United States.
    A Goddard High Resolution spectrograph atlas of echelle observations of the HgMn star χ lupi1999In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 117, no 3, p. 1505-1548Article in journal (Refereed)
    Abstract [en]

    Observations of the ultra-sharp-lined, chemically peculiar star χ Lupi taken by the Goddard High Resolution Spectrograph in echelle mode are presented. Thirty-six intervals of the spectral region between 1249 and 2688 Å are covered with resolving powers in the range 75,000-93,000. Line identifications are provided, and the observed spectra are compared with synthetic spectra calculated using the SYNTHE program and associated line lists with changes to the line lists. The significance of these spectra for the χ Lupi Pathfinder Project and the closely related atomic physics effort is discussed in a companion paper.

  • 7.
    Burheim, Madeleine
    et al.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Observatory, Division of Astrophysics, Department of Physics, Sölvegatan 27, Box 43, 221 00 Lund, Sweden.
    Hartman, Henrik
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Nilsson, Hampus
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Experimental oscillator strengths of Al I lines for near-infrared astrophysical spectroscopy2023In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 672, article id A197Article in journal (Refereed)
    Abstract [en]

    Context. Elemental abundances can be determined from stellar spectra, making it possible to study galactic formation and evolution. Accurate atomic data is essential for the reliable interpretation and modeling of astrophysical spectra. In this work, we perform laboratory studies on neutral aluminium. This element is found, for example, in young, massive stars and it is a key element for tracing ongoing nucleosynthesis throughout the Galaxy. The near-infrared (NIR) wavelength region is of particular importance, since extinction in this region is lower than for optical wavelengths. This makes the NIR wavelength region a better probe for highly obscured regions, such as those located close to the Galactic center.

    Aims. We investigate the spectrum of neutral aluminium with the aim to provide oscillator strengths (f-values) of improved accuracy for lines in the NIR and optical regions (670–4200 nm).

    Methods. Measurements of high-resolution spectra were performed using a Fourier transform spectrometer and a hollow cathode discharge lamp. The f-values were derived from experimental line intensities combined with published radiative lifetimes.

    Results. We report oscillator strengths for 12 lines in the NIR and optical spectral regions, with an accuracy between 2 and 11%, as well as branching fractions for an additional 16 lines.

     

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  • 8.
    Bäckström, E.
    et al.
    Department of Physics, AlbaNova University Center, Stockholm University, SE-106 91 Stockholm, Sweden.
    Gurell, J.
    Department of Physics, AlbaNova University Center, Stockholm University, SE-106 91 Stockholm, Sweden.
    Royen, P.
    Department of Physics, AlbaNova University Center, Stockholm University, SE-106 91 Stockholm, Sweden.
    Mannervik, S.
    Department of Physics, AlbaNova University Center, Stockholm University, SE-106 91 Stockholm, Sweden.
    Norlin, L.
    Department of Nuclear Physics, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden.
    Blackwell-Whitehead, R.
    Lund Observatory, Lund University, SE-221 00 Lund, Box 43, Sweden.
    Hartman, H.
    Lund Observatory, Lund University, SE-221 00 Lund, Box 43, Sweden.
    Nilsson, H.
    Lund Observatory, Lund University, SE-221 00 Lund, Box 43, Sweden.
    The FERRUM project: metastable lifetimes in Cr ii2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 420, no 2, p. 1636-1639Article in journal (Refereed)
    Abstract [en]

    Parity forbidden radiative transitions from metastable levels are observed in spectra of low-density astrophysical plasmas. These lines are used as probes of the physical conditions, made possible due to the long lifetime of their upper level. In a joint effort, the FERRUM project aims to obtain new and accurate atomic data for the iron-group elements, and part of this project concerns forbidden lines. The radiative lifetimes of the metastable energy levels 3 d4(a 3 D)4 s   c4 D 5/2 and 3 d4(a 3 D)4 s   c4 D 7/2 of singly ionized chromium have been measured. The experiment has been performed at the ion storage ring CRYRING. We employed a laser-probing technique developed for measuring long lifetimes. In this article, we present the lifetimes of these levels to be τ5/2= 1.28(16) s and τ7/2= 1.37(7) s, respectively. A comparison with previous theoretical work shows good agreement and the result is discussed in a theoretical context.

  • 9.
    Bäckström, Erik
    et al.
    Department of Physics, Stockholm University.
    Nilsson, H.
    Lund Observatory.
    Engström, L.
    Department of Physics, Lund University.
    Hartman, Henrik
    Malmö högskola, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Observatory.
    Mannervik, S.
    Department of Physics, Stockholm University.
    Experimentally determined oscillator strengths in Rh II2013In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 20, article id 205001Article in journal (Refereed)
    Abstract [en]

    This paper presents new experimentally determined branching fractions and oscillator strengths (log gf) for lines originating from 17 levels belonging to 5 terms of the first excited odd configuration 4d7(4D)5p in Rh II. The intensity calibrated spectra of Rh II have been recorded with a Fourier transform spectrometer between 25000 and 45000 cm−1 (2200–4000 Å). In this region, 49 lines have been identified and measured. By combining the branching fractions obtained from the spectra with previously measured lifetimes, log gf values are reported. The new results are compared with previous theoretical work.

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  • 10.
    Engström, Lars
    et al.
    Department of Physics, Lund University.
    Lundberg, H
    Department of Physics, Lund University.
    Nilsson, Hampus
    Lund Observatory, Lund University.
    Hartman, Henrik
    Malmö högskola, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Observatory, Lund University.
    Bäckström, E
    Department of Physics, Stockholm University.
    The FERRUM project: Experimental transition probabilities from highly excited even 5s levels in Cr ii2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 570, article id A34Article in journal (Refereed)
    Abstract [en]

    We report lifetime measurements of the five levels in the 3d4(a5D)5s e6D term in Cr ii at an energy around 83 000 cm-1, and log(g f ) values for 38 transitions from the investigated levels. The lifetimes are obtained using time-resolved, laser-induced fluorescence on ions from a laser-produced plasma. Since the levels have the same parity as the low-lying states directly populated in the plasma, we used a two-photon excitation scheme. This process is greatly facilitated by the presence of the 3d4(a5D)4p z6F levels at roughly half the energy di erence. The f -values are obtained by combining the experimental lifetimes with branching fractions derived using relative intensities from a hollow cathode lamp recorded with a Fourier transform spectrometer.

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  • 11.
    Eriksson, M.
    et al.
    University of Kalmar, 391 82 Kalmar, Sweden; Space Telescope Science Institute, 3700 San Martin drive, Baltimore, MD 21218, USA.
    Nilsson, Hampus
    Atomic Astrophysics, Lund Observatory, Box 43, 221 00 Lund, Sweden.
    Veenhuizen, H.
    University of Kalmar, 391 82 Kalmar.
    Long, K. S.
    Space Telescope Science Institute, 3700 San Martin drive, Baltimore, MD 21218, USA.
    Modeling of C IV pumped fluorescence of Fe II in symbiotic stars2007In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 477, no 1, p. 255-265Article in journal (Refereed)
  • 12.
    Fivet, V
    et al.
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Biémont, É
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, B-7000 Mons, Belgium; IPNAS, Université de Liège, Sart Tilman, B-4000 Liège, Belgium.
    Engström, L
    Department of Physics, Lund Institute of Technology, PO Box 118, SE-221 00 Lund, Sweden.
    Lundberg, H
    Department of Physics, Lund Institute of Technology, PO Box 118, SE-221 00 Lund, Sweden.
    Nilsson, H
    Lund Observatory, Lund University, PO Box 43, SE-22100 Lund, Sweden.
    Palmeri, P
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Quinet, P
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, B-7000 Mons, Belgium; IPNAS, Université de Liège, Sart Tilman, B-4000 Liège, Belgium.
    Radiative lifetime measurements and calculations in doubly ionized tantalum (Ta III)2007In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 41, no 1, p. 015702-015702Article in journal (Refereed)
    Abstract [en]

    Radiative lifetimes of six odd-parity levels belonging to the 5d26p configuration of doubly ionized tantalum (Ta III) have been measured using the time-resolved-laser-induced- fluorescence technique. Supporting theoretical calculations, including core-polarization effects, have been performed to model configuration interaction and to estimate branching fractions. The excellent agreement between the theoretical and experimental lifetimes allows us to assess the reliability of the 206 calculated transition probabilities. It is expected that this new set of results will be useful to astrophysicists for the investigation of the chemical composition of stars.

  • 13.
    Fivet, V.
    et al.
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Quinet, P.
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, B-7000 Mons, Belgium; IPNAS, Université de Liège, B-4000 Liège, B15 Sart Tilman, Belgium.
    Palmeri, P.
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Biémont, É.
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, B-7000 Mons, Belgium; IPNAS, Université de Liège, B-4000 Liège, B15 Sart Tilman, Belgium.
    Asplund, M.
    Max Planck Institute for Astrophysics, D-85741 Garching, Postfach 1317, Germany.
    Grevesse, N.
    Centre Spatial de Liège, B-4031 Angleur-Liège, Avenue Pré Aily, Belgium; Institut d'Astrophysique et de Géophysique, Université de Liège, B-4000 Liège, Allée du 6 Août,17, B5C, Belgium.
    Sauval, A. J.
    Observatoire Royal de Belgique, B-1180 Bruxelles, Avenue Circulaire, 3, Belgium.
    Engström, L.
    Department of Physics, Lund University, SE-221 00 Lund, PO Box 118, Sweden.
    Lundberg, H.
    Department of Physics, Lund University, SE-221 00 Lund, PO Box 118, Sweden.
    Hartman, H.
    Lund Observatory, Lund University, SE-221 00 Lund, PO Box 43, Sweden.
    Nilsson, H.
    Lund Observatory, Lund University, SE-221 00 Lund, PO Box 43, Sweden.
    Experimental and theoretical radiative decay rates for highly excited ruthenium atomic levels and the solar abundance of ruthenium2009In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 396, no 4, p. 2124-2132Article in journal (Refereed)
    Abstract [en]

    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), A Ru = 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.

  • 14.
    Galcheva, M.
    et al.
    Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, BG-1784 Sofia, Bulgaria.
    Engström, Lars
    Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Lundberg, H.
    Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Nilsson, H.
    Lund Observatory, Lund University, Box 43, SE-22100 Lund, Sweden.
    Hartman, Henrik
    Malmö högskola, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Observatory, Lund University, Box 43, SE-22100 Lund, Sweden.
    Blagoev, K.
    Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, BG-1784 Sofia, Bulgaria.
    Lifetime measurements of even and odd states in neutral terbium (Tb I)2013In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 88, no 4, article id 045304Article in journal (Refereed)
    Abstract [en]

    Radiative lifetimes of 7 odd and 11 even parity states of Tb I (Z = 65) have been measured by the time resolved laser induced fluorescence method (TR-LIF). Experimental data for 9 out of the 18 states are obtained for the first time. The radiative lifetimes presented in this study are in good agreement with previous TR-LIF experimental results but systematically shorter than those obtained by the delayed coincidence technique.

  • 15.
    Gurell, J.
    et al.
    Department of Physics, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden.
    Hartman, H.
    Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Blackwell-Whitehead, R.
    Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Nilsson, H.
    Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Bäckström, E.
    Department of Physics, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden.
    Norlin, L. O.
    Department of Physics, Royal Institute of Technology, AlbaNova University Center, 10691 Stockholm, Sweden.
    Royen, P.
    Department of Physics, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden.
    Mannervik, S.
    Department of Physics, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden.
    The FERRUM project: transition probabilities for forbidden lines in [Fe II] and experimental metastable lifetimes2009In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 508, no 1, p. 525-529Article in journal (Refereed)
    Abstract [en]

    Context. Accurate transition probabilities for forbidden lines are important diagnostic parameters for low-density astrophysical plasmas. In this paper we present experimental atomic data for forbidden [Fe II] transitions that are observed as strong features in astrophysical spectra. Aims. We measure lifetimes for the 3d6 (3G)4sa4 and 3d 6 (3D)4sb4 D1/2 metastable levels in Fe II and experimental transition probabilities for the forbidden transitions 3d7a4F7/2,9/2-3d6( 3G)4sa4.Methods. The lifetimes were measured at the ion storage ring facility CRYRING using a laser probing technique. Astrophysical branching fractions were obtained from spectra of Eta Carinae, obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. The lifetimes and branching fractions were combined to yield absolute transition probabilities.Results. The lifetimes of the a4G11/2 and the b4D1/2 levels have been measured and have the following values, r = 0.75 ± 0.10 s respectively. Furthermore, we have determined the transition probabilities for two forbidden transitions of a 4F7/2,9/2-a4G11/2 at 4243.97 and 4346.85Å. Both the lifetimes and the transition probabilities are compared to calculated values in the literature. 

  • 16.
    Gurell, J.
    et al.
    Department of Physics, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden.
    Nilsson, H.
    Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Engström, L.
    Atomic Physics, Department of Physics, Lund University, Box 118, 22100 Lund, Sweden.
    Lundberg, H.
    Atomic Physics, Department of Physics, Lund University, Box 118, 22100 Lund, Sweden.
    Blackwell-Whitehead, R.
    Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Nielsen, K. E.
    Catholic University of America, Washington, DC 20064, USA; Astrophysics Science Division, Code 667, Goddard Space Flight Center, Greenbelt, MD 20771, USA.
    Mannervik, S.
    Department of Physics, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden.
    The FERRUM project: laboratory-measured transition probabilities for Cr II2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 511, p. A68-A68Article in journal (Refereed)
    Abstract [en]

    Aims. We measure transition probabilities for Cr II transitions from the z 4HJ, z 2DJ, y 4FJ, and y 4GJ levels in the energy range 63 000 to 68 000 cm-1.Methods. Radiative lifetimes were measured using time-resolved laser-induced fluorescence from a laser-produced plasma. In addition, branching fractions were determined from intensity-calibrated spectra recorded with a UV Fourier transform spectrometer. The branching fractions and radiative lifetimes were combined to yield accurate transition probabilities and oscillator strengths.Results. We present laboratory measured transition probabilities for 145 Cr II lines and radiative lifetimes for 14 Cr II levels. The laboratory-measured transition probabilities are compared to the values from semi-empirical calculations and laboratory measurements in the literature.

  • 17.
    Hansen, C.J.
    et al.
    European Southern Observatory (ESO), Karl-Schwarschild-Str. 2, 85748 Garching b. München, Germany; ‹.
    Primas, F.
    European Southern Observatory (ESO), Karl-Schwarschild-Str. 2, 85748 Garching b. München, Germany.
    Hartman, Henrik
    Malmö högskola, School of Technology (TS). Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, 22100 Lund, Sweden.
    Kratz, K.-L.
    Max-Planck-Institut für Chemie, Otto-Hahn-Institut, Joh.-J-Becherweg 27, 55128 Mainz, Germany.
    Wanajo, Shinya
    Technische Universität München, Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany; Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching Germany; National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, 181-8588 Tokyo, Japan.
    Leibundgut, B.
    European Southern Observatory (ESO), Karl-Schwarschild-Str. 2, 85748 Garching b. München, Germany.
    Farouqi, K.
    Max-Planck-Institut für Chemie, Otto-Hahn-Institut, Joh.-J-Becherweg 27, 55128 Mainz, Germany; Landessternwarte Heidelberg (LSW, ZAH), Königstuhl 12, 69117 Heidelberg, Germany.
    Hallmann, O
    Max-Planck-Institut für Chemie, Otto-Hahn-Institut, Joh.-J-Becherweg 27, 55128 Mainz, Germany.
    Christlieb, N.
    Landessternwarte Heidelberg (LSW, ZAH), Königstuhl 12, 69117 Heidelberg, Germany.
    Nilsson, Hampus
    Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, 22100 Lund, Sweden.
    Silver and palladium help unveil the nature of a second r-process2012In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 545, no (A31), article id A31Article in journal (Refereed)
    Abstract [en]

    Context. The rapid neutron-capture process, which created about half of the heaviest elements in the solar system, is believed to have been unique. Many recent studies have shown that this uniqueness is not true for the formation of lighter elements, in particular those in the atomic number range 38 < Z < 48. Among these, palladium (Pd) and especially silver (Ag) are expected to be key indicators of a possible second r-process, but until recently they have been studied only in a few stars. We therefore target Pd and Ag in a large sample of stars and compare these abundances to those of Sr, Y, Zr, Ba, and Eu produced by the slow (s-) and rapid (r-) neutron-capture processes. Hereby we investigate the nature of the formation process of Ag and Pd. Aims. We study the abundances of seven elements (Sr, Y, Zr, Pd, Ag, Ba, and Eu) to gain insight into the formation process of the elements and explore in depth the nature of the second r-process. Methods. By adopting a homogeneous one-dimensional local thermodynamic equilibrium (1D LTE) analysis of 71 stars, we derive stellar abundances using the spectral synthesis code MOOG, and the MARCS model atmospheres. We calculate abundance ratio trends and compare the derived abundances to site-dependent yield predictions (low-mass O-Ne-Mg core-collapse supernovae and parametrised high-entropy winds), to extract characteristics of the second r-process. Results. The seven elements are tracers of different (neutron-capture) processes, which in turn allows us to constrain the formation process(es) of Pd and Ag. The abundance ratios of the heavy elements are found to be correlated and anti-correlated. These trends lead to clear indications that a second/weak r-process, is responsible for the formation of Pd and Ag. On the basis of the comparison to the model predictions, we find that the conditions under which this process takes place differ from those for the main r-process in needing lower neutron number densities, lower neutron-to-seed ratios, and lower entropies, and/or higher electron abundances. Conclusions. Our analysis confirms that Pd and Ag form via a rapid neutron-capture process that differs from the main r-process, the main and weak s-processes, and charged particle freeze-outs. We find that this process is efficiently working down to the lowest metallicity sampled by our analysis ([Fe/H] = −3.3). Our results may indicate that a combination of these explosive sites is needed to explain the variety in the observationally derived abundance patterns.

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  • 18.
    Hanstorp, Dag
    et al.
    University of Gothenburg.
    Hartman, HenrikMalmö högskola, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund University.Engström, LarsLund University.Nilsson, HampusLund University.Salomonson, StenUniversity of Gothenburg.
    EGAS 44th Conference of the European Group on Atomic Systems - abstract volume2012Conference proceedings (editor) (Refereed)
  • 19.
    Hartman, Henrik
    et al.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Observatory.
    Burheim, Madeleine
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Observatory.
    Nilsson, Hampus
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Observatory.
    Li, Wenxian
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Jönsson, Per
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Laboratory Atomic Astrophysics for near-infrared Stellar Spectroscopy2021Conference paper (Other academic)
    Abstract [en]

    Astronomical infrared observations are of increasing importance for stellar spectroscopy. The analysis of element abundance relies on high-quality observations, stellar models, and ultimately on accurate atomic data. With the growing number of near-IR astronomical observations and surveys, the absence of highaccuracy data is becoming apparent and a severe limiting factor.We run a program to take up the task to provide evaluated, high-accuracy atomic data for important transitions in the near-infrared spectral region, mainly 1-5 microns. A combinations of both experimental and theoretical techniques is used, to provide complete sets of data with a low uncertainty. FTS measurements of a discharge are combined with laser induced fluorescence techniques, and GRASP2k and ATSP2k atomic structure calculations for the theoretical values.

  • 20.
    Hartman, Henrik
    et al.
    Malmö högskola, Faculty of Technology and Society (TS). Lund Observatory, Lund University, Box 43, 221 00 Lund, Sweden.
    Engström, Lars
    Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden.
    Lundberg, Hans
    Lund Observatory, Lund University, Box 43, 221 00 Lund, Sweden; Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden.
    Nilsson, Hampus
    Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden.
    Quinet, Pascal
    Physique Atomique et Astrophysique, Université de Mons, 7000 Mons, Belgium; IPNAS, Université de Liège, 4000 Liège, Belgium.
    Fivet, Vanessa
    Physique Atomique et Astrophysique, Université de Mons, 7000 Mons, Belgium.
    Palmeri, Patrick
    Physique Atomique et Astrophysique, Université de Mons, 7000 Mons, Belgium.
    Malcheva, Galina
    Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria.
    Blagoev, Kiril
    Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia, Bulgaria.
    Radiative data for highly excited 3d84d levels in Ni II from laboratory measurements and atomic calculations2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 600, article id A108Article in journal (Refereed)
    Abstract [en]

    Aims: This work reports new experimental radiative lifetimes and calculated oscillator strengths for transitions from 3d84d levels of astrophysical interest in singly ionized nickel. Methods: Radiative lifetimes of seven high-lying levels of even parity in Ni II (98 400-100 600 cm-1) have been measured using the time-resolved laser-induced fluorescence method. Two-step photon excitation of ions produced by laser ablation has been utilized to populate the levels. Theoretical calculations of the radiative lifetimes of the measured levels and transition probabilities from these levels are reported. The calculations have been performed using a pseudo-relativistic Hartree-Fock method, taking into account core polarization effects. Results: A new set of transition probabilities and oscillator strengths has been deduced for 477 Ni II transitions of astrophysical interest in the spectral range 194-520 nm depopulating even parity 3d84d levels. The new calculated gf-values are, on the average, about 20% higher than a previous calculation and yield lifetimes within 5% of the experimental values.

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  • 21.
    Hartman, Henrik
    et al.
    Malmö högskola, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Observatory, Lund University.
    Nilsson, Hampus
    Lund Observatory, Lund University.
    Engström, L
    Department of Physics, Lund University.
    Lundberg, H
    Department of Physics, Lund University.
    The FERRUM project: Experimental lifetimes and transition probabilities from highly excited even 4d levels in Fe ii2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 584, no A24, article id A24Article in journal (Refereed)
    Abstract [en]

    We report lifetime measurements of the 6 levels in the 3d6(5D)4d e6G term in Fe ii at an energy of 10.4 eV, and f -values for 14 transitions from the investigated levels. The lifetimes were measured using time-resolved laser-induced fluorescence on ions in a laserproduced plasma. The high excitation energy, and the fact that the levels have the same parity as the the low-lying states directly populated in the plasma, necessitated the use of a two-photon excitation scheme. The probability for this process is greatly enhanced by the presence of the 3d6(5D)4p z6F levels at roughly half the energy di erence. The f -values are obtained by combining the experimental lifetimes with branching fractions derived using relative intensities from a hollow cathode discharge lamp recorded with a Fourier transform spectrometer. The data is important for benchmarking atomic calculations of astrophysically important quantities and useful for spectroscopy of hot stars.

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  • 22.
    Hartman, Henrik
    et al.
    Department of Astronomy and Theoretical Physics, Lund University, Box 43, SE-221 00 Lund, Sweden.
    Nilsson, Hampus
    Department of Astronomy and Theoretical Physics, Lund University, Box 43, SE-221 00 Lund, Sweden.
    Engström, Lars
    Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Lundberg, Hans
    Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Palmeri, Patrick
    Astrophysique et Spectroscopie, Université de Mons-UMONS, Place du Parc, 20, B-7000 Mons, Belgium.
    Quinet, Pascal
    Astrophysique et Spectroscopie, Université de Mons-UMONS, Place du Parc, 20, B-7000 Mons, Belgium; IPNAS, Université de Liège, B-4000 Liège, Belgium.
    Biémont, Émile
    Astrophysique et Spectroscopie, Université de Mons-UMONS, Place du Parc, 20, B-7000 Mons, Belgium; IPNAS, Université de Liège, B-4000 Liège, Belgium.
    Experimental and theoretical lifetimes and transition probabilities in Sb i2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, no 5, article id 052512Article in journal (Refereed)
    Abstract [en]

    We present experimental atomic lifetimes for 12 levels in Sb i. The levels belong to the 5p2(3P)6s 2P, 4P, and 5p2(3P)5d 4P, 4F, and 2F terms. The lifetimes were measured using time-resolved laser-induced fluorescence. In addition, we report calculations of transition probabilities in Sb i using a multiconfigurational Dirac-Hartree-Fock method. The physical model was tested through comparisons between theoretical and experimental lifetimes for 5d and 6s levels. The lifetimes of the 5d 4F3/2,5/2,7/2 levels (19.5, 7.8, and 54 ns, respectively) depend strongly on the J value. This is explained by different degrees of level mixing for the different levels in the 4F term.

  • 23.
    Holmes, Charlotte
    et al.
    Blackett Laboratory, Dept. Physics, Imperial College London, London SW7 2AZ, UK.
    Pickering, Juliet
    Blackett Laboratory, Dept. Physics, Imperial College London, London SW7 2AZ, UK.
    Ruffoni, Matthew
    Blackett Laboratory, Dept. Physics, Imperial College London, London SW7 2AZ, UK.
    Blackwell-Whitehead, Richard
    Blackett Laboratory, Dept. Physics, Imperial College London, London SW7 2AZ, UK.
    Nilsson, Hampus
    Blackett Laboratory, Dept. Physics, Imperial College London, London SW7 2AZ, UK.
    Engström, Lars
    Blackett Laboratory, Dept. Physics, Imperial College London, London SW7 2AZ, UK.
    Hartman, Henrik
    Blackett Laboratory, Dept. Physics, Imperial College London, London SW7 2AZ, UK.
    Lundberg, Hans
    Blackett Laboratory, Dept. Physics, Imperial College London, London SW7 2AZ, UK.
    Belmonte, M
    Blackett Laboratory, Dept. Physics, Imperial College London, London SW7 2AZ, UK.
    Experimentally Measured Radiative Lifetimes and Oscillator Strengths in Neutral Vanadium2016In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 224, no 2, article id 35Article in journal (Refereed)
    Abstract [en]

    We report a new study of the V i atom using a combination of time-resolved laser-induced fluorescence and Fourier transform spectroscopy that contains newly measured radiative lifetimes for 25 levels between 24,648 cm-1 and 37,518 cm-1 and oscillator strengths for 208 lines between 3040 and 20000 Å from 39 upper energy levels. Thirteen of these oscillator strengths have not been reported previously. This work was conducted independently of the recent studies of neutral vanadium lifetimes and oscillator strengths carried out by Den Hartog et al. and Lawler et al., and thus serves as a means to verify those measurements. Where our data overlap with their data, we generally find extremely good agreement in both level lifetimes and oscillator strengths. However, we also find evidence that Lawler et al. have systematically underestimated oscillator strengths for lines in the region of 9000 ± 100 Å. We suggest a correction of 0.18 ± 0.03 dex for these values to bring them into agreement with our results and those of Whaling et al. We also report new measurements of hyperfine structure splitting factors for three odd levels of V i lying between 24,700 and 28,400 cm-1.

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  • 24.
    Ivarsson, S.
    et al.
    Atomic Astrophysics, Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden.
    Andersen, J.
    Astronomical Observatory, Niels Bohr Institute for Astronomy, Physics & Geophysics, Juliane Maries Vej 30, 2100 Copenhagen, Denmark; Nordic Optical Telescope Scientific Association, La Palma, Canary Islands, Spain.
    Nordström, B.
    Atomic Astrophysics, Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden; Astronomical Observatory, Niels Bohr Institute for Astronomy, Physics & Geophysics, Juliane Maries Vej 30, 2100 Copenhagen, Denmark.
    Dai, X.
    Atomic Physics, Department of Physics, Lund Institute of Technology, PO Box 118, 22100 Lund, Sweden.
    Johansson, S.
    Atomic Astrophysics, Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden.
    Lundberg, H.
    Atomic Physics, Department of Physics, Lund Institute of Technology, PO Box 118, 22100 Lund, Sweden.
    Nilsson, H.
    Atomic Astrophysics, Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden.
    Hill, V.
    GEPI, Observatoire de Paris-Meudon (UMR 8111), DASGAL, 2 pl. Jules Janssen, 92195 Meudon Cedex, France.
    Lundqvist, M.
    Atomic Astrophysics, Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden.
    Wyart, J. F.
    Laboratoire Aimé Cotton, Centre National de la Recherche Scientifique, Orsay, France.
    Improved oscillator strengths and wavelengths for Os I and Ir I, and new results on earlyr-process nucleosynthesis2003In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 409, no 3, p. 1141-1149Article in journal (Refereed)
    Abstract [en]

    The radioactive decay of 238U and 232Th has recently been used to determine ages for some of the oldest stars in the Universe. This has highlighted the need for accurate observational constraints on production models for the heaviest r-process elements which might serve as stable references, notably osmium and iridium. In order to provide a firmer basis for the observed abundances, we have performed laser-induced fluorescence measurements and Fourier Transform Spectroscopy to determine new radiative lifetimes and branching fractions for selected levels in Os I and Ir I. From these data, we determine new absolute oscillator strengths and improved wavelengths for 18 Os I and 4 Ir I lines. A reanalysis of VLT spectra of CS 31082-001 and new results for other stars with Os and Ir detections show that (i): the lines in the UV and λ 4260 Å yield reliable Os abundances, while those at   4135, 4420 Å are heavily affected by blending; (ii): the Os and Ir abundances are identical in all the stars; (iii): the heavy-element abundances in very metal-poor stars conform closely to the scaled solar r-process pattern throughout the range 56 ≤ Z ≤ 77; and (iv): neither Os or Ir nor any lighter species are suitable as reference elements for the radioactive decay of Th and U.

     

  • 25.
    Johansson, S.
    et al.
    Atomic Astrophysics, Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    Derkatch, A.
    Physics Department, Stockholm University, Stockholm, Sweden.
    Donnelly, M. P.
    Department of Applied Mathematics and Theoretical Physics, The Queens University of Belfast, Belfast, Northern Ireland.
    Hartman, Henrik
    Atomic Astrophysics, Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    Hibbert, A.
    Department of Applied Mathematics and Theoretical Physics, The Queens University of Belfast, Belfast, Northern Ireland.
    Karlsson, H.
    Atomic Astrophysics, Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    Kock, M.
    Institute for Atomic and Molecular Physics, University of Hannover, Hannover, Germany.
    Li, Z. S.
    Department of Physics, Lund Institute of Technology, Lund, Sweden.
    Leckrone, D. S.
    NASA / Goddard Space Flight Center, Greenbelt, Maryland, USA.
    Litzén, U.
    Atomic Astrophysics, Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    Lundberg, H.
    Department of Physics, Lund Institute of Technology, Lund, Sweden.
    Mannervik, S.
    Physics Department, Stockholm University, Stockholm, Sweden.
    Norlin, L-O.
    Physics Department, Royal Institute of Technology, Stockholm, Sweden.
    Nilsson, H.
    Atomic Astrophysics, Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    Pickering, J.
    Physics Department, Blackett Laboratory, Imperial College, London, UK.
    Raassen, T.
    Astronomical Institute "Anton Pannekoek", University of Amsterdam, Amsterdam, The Netherlands.
    Rostohar, D.
    Physics Department, Stockholm University, Stockholm, Sweden.
    Royen, P.
    Physics Department, Stockholm University, Stockholm, Sweden.
    Schmitt, A.
    Fachbereich Physik, University of Kaislerslautern, Kaiserslautern, Germany.
    Johanning, M.
    Institute for Atomic and Molecular Physics, University of Hannover, Hannover, Germany.
    Sikström, C. M.
    Atomic Astrophysics, Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    Smith, P. L.
    Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA.
    Svanberg, S.
    Department of Physics, Lund Institute of Technology, Lund, Sweden.
    Wahlgren, G. M.
    Atomic Astrophysics, Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    The FERRUM Project: New f-value Data for Fe II and Astrophysical Applications2002In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T100, no 1, p. 71-71Article in journal (Refereed)
    Abstract [en]

    We present the FERRUM Project, an international collaboration aiming at a production and evaluation of oscillator strengths (transition probabilities) of selected spectral lines of singly ionized iron group elements, that are of astrophysical relevance. The results obtained include measurements and calculations of permitted and forbidden lines of Fe II. The data have been applied to both emission and absorption lines in astrophysical spectra. We make comparisons between experimental, theoretical and astrophysical f-values. We give a general review of the various measurements, and discuss the UV8 multiplet of Fe II around 1610 Å in detail.

  • 26.
    Kristensson, Elias
    et al.
    Department of Physics, Lund University, Professorsgatan 1, SE-22363, Lund, Sweden.
    Bood, Joakim
    Department of Physics, Lund University, Professorsgatan 1, SE-22363, Lund, Sweden.
    Alden, Marcus
    Department of Physics, Lund University, Professorsgatan 1, SE-22363, Lund, Sweden.
    Nordström, Emil
    Department of Physics, Lund University, Professorsgatan 1, SE-22363, Lund, Sweden.
    Zhu, Jiajian
    Department of Physics, Lund University, Professorsgatan 1, SE-22363, Lund, Sweden.
    Huldt, Sven
    Department of Astronomy and Theoretical Physics, Lund University, Sölvegatan 27, SE-22362, Lund, Sweden.
    Bengtsson, Per-Erik
    Department of Physics, Lund University, Professorsgatan 1, SE-22363, Lund, Sweden.
    Nilsson, Hampus
    Department of Astronomy and Theoretical Physics, Lund University, Sölvegatan 27, SE-22362, Lund, Sweden.
    Berrocal, Edouard
    Department of Physics, Lund University, Professorsgatan 1, SE-22363, Lund, Sweden.
    Ehn, Andreas
    Department of Physics, Lund University, Professorsgatan 1, SE-22363, Lund, Sweden.
    Stray light suppression in spectroscopy using periodic shadowing2014In: Optics Express, E-ISSN 1094-4087, Vol. 22, no 7, p. 7711-7711Article in journal (Refereed)
    Abstract [en]

    It is well known that spectroscopic measurements suffer from an interference known as stray light, causing spectral distortion that reduces measurement accuracy. In severe situations, stray light may even obscure the existence of spectral lines. Here a novel general method is presented, named Periodic Shadowing, that enables effective stray light elimination in spectroscopy and experimental results are provided to demonstrate its capabilities and versatility. Besides its efficiency, implementing it in a spectroscopic arrangement comes at virtually no added experimental complexity.

     

  • 27.
    Lennartsson, T
    et al.
    Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    Nilsson, H
    Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    Blackwell-Whitehead, R
    Department of Physics, Lund Institute of Technology, Box 118, SE-221 00 Lund, Sweden.
    Engström, L
    Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    Huldt, S
    Lund Observatory, Box 43, SE-221 00 Lund, Sweden.
    Branching fractions in singly ionized tungsten2011In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 44, no 24, p. 245001-245001Article in journal (Refereed)
    Abstract [en]

    The intensity-calibrated spectra of W II have been recorded in the spectral interval 23 000–51 300 cm−1 (1950–4350 Å), using the FT500 UV Fourier Transform Spectrometer at Lund Observatory. Combining the intensity data in this work with lifetimes previously measured using the time-resolved laser-induced-fluorescence (TR-LIF) technique resulted in transition probabilities and log gf values for 95 transitions in W II, originating from nine different upper levels with energies between 47 179 and 55 392 cm−1. Of these transitions, 85 have never been measured before. The new data are compared with theoretical calculations and with previously measured values when available.

  • 28.
    Ljung, G.
    et al.
    Atomic Astrophysics, Lund Observatory, Box 43, 221 00 Lund, Sweden.
    Nilsson, H.
    Atomic Astrophysics, Lund Observatory, Box 43, 221 00 Lund, Sweden.
    Asplund, M.
    Research School of Astronomy and Astrophysics, Australian National University, Mt. Stromlo Observatory, Cotter Rd., Weston, ACT 2611, Australia.
    Johansson, S.
    Atomic Astrophysics, Lund Observatory, Box 43, 221 00 Lund, Sweden.
    New and improved experimental oscillator strengths in Zr II and the solar abundance of zirconium2006In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 456, no 3, p. 1181-1185Article in journal (Refereed)
    Abstract [en]

    Using the Fourier Transform Spectrometer at Lund Observatory, intensity calibrated spectra of singly ionized zirconium have been recorded and analyzed. Oscillator strengths for 263 Zr II spectral lines in the region 2500-5400 A have been derived by combining new experimental branching fractions with previously measured radiative lifetimes. The transitions combine 34 odd parity levels with 29 low metastable levels between 0 and 2.4 eV. The experimental branching fractions have been compared with theoretical values and the oscillator strengths with previously published data when available. The oscillator strengths have been employed to derive the solar photospheric Zr abundance based on both ID and 3D model atmospheres. Based on the seven best and least perturbed Zr II lines in the solar disk-center spectrum, we determine the solar Zr abundance to log εZr = 2.58 ±0.02 when using a 3D hydrodynamical solar model atmosphere. The new value is in excellent agreement with the meteoritic Zr abundance. © ESO 2006.

  • 29.
    Lundberg, H
    et al.
    Department of Physics, Lund University, PO Box 118, SE-221 00 Lund, Sweden.
    Engström, L
    Department of Physics, Lund University, PO Box 118, SE-221 00 Lund, Sweden.
    Hartman, H
    Lund Observatory, Lund University, PO Box 43, SE-221 00 Lund, Sweden.
    Nilsson, H
    Lund Observatory, Lund University, PO Box 43, SE-221 00 Lund, Sweden.
    Palmeri, P
    Astrophysique et Spectroscopie, Université de Mons—UMONS, 20 Place du Parc, B-7000 Mons, Belgium.
    Quinet, P
    Astrophysique et Spectroscopie, Université de Mons—UMONS, 20 Place du Parc, B-7000 Mons, Belgium; IPNAS, Université de Liège, B15 Sart Tilman, B-4000 Liège, Belgium.
    Biémont, É
    Astrophysique et Spectroscopie, Université de Mons—UMONS, 20 Place du Parc, B-7000 Mons, Belgium; IPNAS, Université de Liège, B15 Sart Tilman, B-4000 Liège, Belgium.
    Lifetime measurements and transition probabilities in Mo II2010In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 43, no 8, p. 085004-085004Article in journal (Refereed)
    Abstract [en]

    Lifetimes have been measured using time-resolved laser-induced fluorescence for 16 odd levels in the doublet, quartet and sextet systems of Mo II, with energies in the range 48 000–61 000 cm−1. Absolute transition probabilities and oscillator strengths are determined for 110 UV and visible transitions (208 < λ < 485 nm) from a combination of experimental lifetimes and theoretical branching fractions. The theoretical results are obtained using the HFR method including core polarization effects.

  • 30.
    Lundberg, H.
    et al.
    Department of Physics, Lund Institute of Technology, PO Box 118, 22100 Lund, Sweden.
    Johansson, S.
    Department of Physics, Lund University, PO Box 118, 22100 Lund, Sweden.
    Nilsson, H.
    Department of Physics, Lund University, PO Box 118, 22100 Lund, Sweden.
    Zhang, Z.
    Department of Physics, Lund Institute of Technology, PO Box 118, 22100 Lund, Sweden.
    New laboratory lifetime measurements of U II for the uranium cosmochronometer2001In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 372, no 3, p. L50-L52Article in journal (Refereed)
    Abstract [en]

    We present new measurements of radiative lifetimes for six energy levels of singly ionized uranium, U II, using laser-induced fluorescence technique. One of the levels, 5f36d7p6M13/2 at 26191 cm-1, decays by a transition at 3859.6 Å. This line has recently been observed in the spectrum of the metal-poor star CS1082-001, the first detection of uranium outside the solar system. The λ3859 line can be used as the presently most accurate cosmochronometer (Cayrel et al. 2001). Our value of the lifetime of the 6M13/2 level is 18.6 ± 0.7 ns, and it confirms the f-value used in the Nature article by Cayrel et al. (2001), which is based on an experimental lifetime of 20 ± 5 ns (Chen & Borzileri 1981). The new measurement also removes the doubt about the choice between that value and other f-values in the literature, differing by a factor of 3. Adopting the same branching fraction as Chen & Borzileri (1981) for the 3859.6 Å line, we derive a gf-value of 0.68, which is 8% higher than the value used by Cayrel et al. (2001). Of significance for the chronometer is also the reduced uncertainty of the radiative lifetime, 4% compared to 25%, and consequently of the f-value, which should decrease the uncertainty in the determination of the stellar age considerably.

  • 31.
    Lundberg, Hans
    et al.
    Department of Physics, Lund University, PO Box 118, SE-221 00 Lund, Sweden.
    Hartman, Henrik
    Malmö högskola, Faculty of Technology and Society (TS). Department of Astronomy and Theoretical Physics, Lund University, PO Box 43, SE-221 00 Lund, Sweden.
    Engström, Lars
    Department of Physics, Lund University, PO Box 118, SE-221 00 Lund, Sweden.
    Nilsson, Hampus
    Department of Physics, Lund University, PO Box 118, SE-221 00 Lund, Sweden.
    Persson, Anders
    Department of Physics, Lund University, PO Box 118, SE-221 00 Lund, Sweden.
    Palmeri, Patrick
    Physique Atomique et Astrophysique, Université de Mons, B-7000 Mons, Belgium.
    Quinet, P.
    Physique Atomique et Astrophysique, Université de Mons, B-7000 Mons, Belgium; IPNAS, Université de Liège, B-4000 Liège, Belgium.
    Fivet, Vanessa
    Physique Atomique et Astrophysique, Université de Mons, B-7000 Mons, Belgium.
    Malcheva, G
    Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, BG-1784 Sofia, Bulgaria.
    Blagoev, Kiril
    Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, BG-1784 Sofia, Bulgaria.
    Oscillator strengths for high-excitation Ti II from laboratory measurements and calculations2016In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 460, no 1, p. 356-362Article in journal (Refereed)
    Abstract [en]

    This work reports new experimental radiative lifetimes of six 3d2(3F)5s levels in singly ionized titanium, with an energy around 63 000 cm−1 and four 3d2(3F)4p odd parity levels where we confirm previous investigations. Combining the new 5s lifetimes with branching fractions measured previously by Pickering et al., we report 57 experimental log gf values for transitions from the 5s levels. The lifetime measurements are performed using time-resolved laser-induced fluorescence on ions produced by laser ablation. One- and two-step photon excitation is employed to reach the 4p and 5s levels, respectively. Theoretical calculations of the radiative lifetimes of the measured levels as well as of oscillator strengths for 3336 transitions from these levels are reported. The calculations are carried out by a pseudo relativistic Hartree–Fock method taking into account core-polarization effects. The theoretical results are in a good agreement with the experiments and are needed for accurate abundance determinations in astronomical objects.

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  • 32.
    Lundqvist, M.
    et al.
    Atomic Astrophysics, Lund Observatory, Lund University, Box 43, 221 00 Lund.
    Nilsson, H.
    Atomic Astrophysics, Lund Observatory, Lund University, Box 43, 221 00 Lund.
    Wahlgren, G. M.
    Atomic Astrophysics, Lund Observatory, Lund University, Box 43, 221 00 Lund.
    Lundberg, H.
    Atomic Physics, Department of Physics, Lund Institute of Technology, Box 118, 221 00 Lund, Sweden.
    Xu, H. L.
    Atomic Physics, Department of Physics, Lund Institute of Technology, Box 118, 221 00 Lund, Sweden; Department of Physics, Jilin University, ChangChun, 130023, PR China; Department of Physics, Engineering and Optics, Laval University, Quebec City, G1K 7P4, Canada.
    Jang, Z.-K.
    Department of Physics, Jilin University, ChangChun, 130023, PR China.
    Leckrone, D. S.
    Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center, Code 681, Greenbelt, MD, 20771, USA.
    Improved oscillator strengths and wavelengths in Hf II, with applications to stellar elemental abundances2006In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 450, no 1, p. 407-413Article in journal (Refereed)
    Abstract [en]

    Aims. We present new and improved radiative lifetimes for eight levels in Hf I and 18 levels in Hf II, along with oscillator strengths and wavelengths for 195 transitions in Hf II. With these data we determine the abundance of hafnium in two chemically peculiar stars: the hot-Am star HR 3383 and the HgMn star chi; Lupi, and discuss the implications of the new data to the hafnium abundance for the Sun and the metal-poor galactic halo stars CS 22892-052 and CS 31082-001. Methods. The oscillator strengths are derived by combining radiative lifetimes measured with the laser induced fluorescence technique and branching fractions determined from intensity calibrated Fourier transform spectra. The hafnium abundance in the two sharp-lined peculair stars is determined by comparison of spectra obtained from instruments onboard the Hubble Space Telescope with synthetic spectra, while the abundance of hafnium in the solar photosphere and the metal-poor halo stars is discussed in terms of rescaling previous investigations using the new gf values. Results. The abundance enhancement of hafnium has been determined in HR 3383 to be +1.7 dex and that for χ Lupi A is +1.3 dex. In the course of the analysis we have also determined an abundance enhancement for molybdenum in HR 3383 to be +1.2 dex, which is similar to that known for χ Lupi A. The abundances in the metal-poor halo stars CS 31082-001 and CS 22892-052 were rescaled to log e(Hf) = -0.75 and -0.82 respectively, with smaller 1σ uncertainty. This has the effect of improving the theoretical fits of r-process nucleosynthesis to abundance data for heavy elements. The change of gf values also implies that the hafnium abundance in the solar photosphere should be reduced by up to 0.2 dex, thereby inducing a discrepancy with the meteoritic hafnium abundance.

  • 33.
    Malcheva, G.
    et al.
    Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, BG-1784 Sofia, Bulgaria.
    Mayo, R.
    CIEMAT, Avda. Complutense, 22, 28040 Madrid, Spain; Faculty of Physics, University Complutense de Madrid, E-28040 Madrid, Spain.
    Ortiz, M.
    Faculty of Physics, University Complutense de Madrid, E-28040 Madrid, Spain.
    Ruiz, J.
    Faculty of Physics, University Complutense de Madrid, E-28040 Madrid, Spain.
    Engström, L.
    Department of Physics, Lund Institute of Technology, PO Box 118, S-221 00 Lund, Sweden.
    Lundberg, H.
    Department of Physics, Lund Institute of Technology, PO Box 118, S-221 00 Lund, Sweden.
    Nilsson, H.
    Lund Observatory, PO Box 43, S-221 00 Lund, Sweden.
    Quinet, P.
    IPNAS (Bât. B15), University of Liège, Sart Tilman, B-4000 Liège, Belgium; Astrophysics and Spectroscopy, University of Mons-Hainaut, B-7000 Mons, Belgium.
    Biémont, É.
    IPNAS (Bât. B15), University of Liège, Sart Tilman, B-4000 Liège, Belgium; Astrophysics and Spectroscopy, University of Mons-Hainaut, B-7000 Mons, Belgium.
    Blagoev, K.
    Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, BG-1784 Sofia, Bulgaria.
    Radiative decay data for highly excited Zr I levels 2009In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 395, no 3, p. 1523-1528Article in journal (Refereed)
  • 34.
    Malcheva, G.
    et al.
    Institute of Solid State Physics 'Acad. G. Nadjakov', Bulgarian Academy of Sciences, BG - 1784 Sofia, 72 TzarigradskoChaussee, Bulgaria.
    Nilsson, H.
    Lund Observatory, Lund University, S-221 00 Lund, PO Box 43, Sweden.
    Engström, L.
    Department of Physics, Lund University, S-221 00 Lund, PO Box 118, Sweden.
    Lundberg, H.
    Department of Physics, Lund University, S-221 00 Lund, PO Box 118, Sweden.
    Biémont, É.
    IPNAS (Bât. B15), University of Liège, SartTilman, B-4000 Liège, Belgium; Astrophysics and Spectroscopy, University of Mons-UMONS, B-7000 Mons, Belgium.
    Palmeri, P.
    Astrophysics and Spectroscopy, University of Mons-UMONS, B-7000 Mons, Belgium.
    Quinet, P.
    IPNAS (Bât. B15), University of Liège, SartTilman, B-4000 Liège, Belgium; Astrophysics and Spectroscopy, University of Mons-UMONS, B-7000 Mons, Belgium.
    Blagoev, K.
    Institute of Solid State Physics 'Acad. G. Nadjakov', Bulgarian Academy of Sciences, BG - 1784 Sofia, 72 TzarigradskoChaussee, Bulgaria.
    Radiative parameters of Nb I excited states2011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 412, no 3, p. 1823-1827Article in journal (Refereed)
    Abstract [en]

    Radiative lifetimes of 17 excited levels of Nbi, in the energy range 27400-47700 cm-1 (5p y 6D°9/2, 5p x 6D°7/2, 5p w 4G°7/2,9/2,11/2, 5s5p v 4D°1/2,3/2,5/2,7/2, 5s6p n 4D°1/2,3/2,5/2,7/2, 5s6p o 4F°3/2,5/2,7/2,9/2), have been measured. For 15 of these levels, the lifetimes are obtained for the first time. The lifetimes were measured using the time-resolved laser-induced fluorescence technique and the experiments are complemented by a theoretical investigation using a relativistic Hartree-Fock method including core polarization. By combining the experimental lifetimes and the calculated branching fractions, we obtain transition probabilities for the individual de-excitation channels from the investigated levels

  • 35.
    Malcheva, G.
    et al.
    Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, BG - 1784 Sofia, Bulgaria.
    Yoca, S. Enzonga
    IPNAS (Bˆat. B15), University of Li`ege, Sart Tilman, B-4000 Li`ege, Belgium; CEPAMOQ, Faculty of Sciences, University of Douala, PO Box 8580, Douala, Cameroon.
    Mayo, R.
    CIEMAT, Avda. Complutense, 22, 28040 Madrid, Spain; Faculty of Physics, Univ. Complutense de Madrid, E-28040 Madrid, Spain.
    Ortiz, M.
    Faculty of Physics, Univ. Complutense de Madrid, E-28040 Madrid, Spain.
    Engström, L.
    Department of Physics, Lund University, PO Box 118, S-221 00 Lund, Sweden.
    Lundberg, H.
    Department of Physics, Lund University, PO Box 118, S-221 00 Lund, Sweden.
    Nilsson, H.
    Lund Observatory, Lund University, PO Box 43, S-221 00 Lund, Sweden.
    Biémont, É.
    Astrophysics and Spectroscopy, University of Mons-Hainaut, B-7000 Mons, Belgium.
    Blagoev, K.
    Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, BG - 1784 Sofia, Bulgaria.
    Radiative lifetimes and transition probabilities in Hf I and Hf III2009In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 396, no 4, p. 2289-2294Article in journal (Refereed)
    Abstract [en]

    The infrared (IR) atomic spectral lines that can be observed in laboratory and astrophysical spectra depend both on the atomic structure and the physical conditions in which the atoms reside. This is a brief review of IR laboratory spectroscopy, discussing which lines in the wavelength interval 1–5 μm can be expected to be seen in different astrophysical sources.

  • 36.
    Nilsson, H.
    et al.
    Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Andersson, J.
    Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden.
    Engström, L.
    Department of Physics, Lund University, Box 118, 22100 Lund, Sweden.
    Lundberg, H.
    Department of Physics, Lund University, Box 118, 22100 Lund, Sweden.
    Hartman, H.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Experimental transition probabilities for 4p-4d spectral lines in V II2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 622, article id A154Article in journal (Refereed)
    Abstract [en]

    Aims. We aim to measure lifetimes of levels belonging to the 3d(3)(F-4)4d subconfiguration in V II, and derive absolute transition probabilities by combining the lifetimes with experimental branching fractions. Methods. The lifetimes were measured using time-resolved laser-induced fluorescence in a two-photon excitation scheme. The branching fractions were measured in intensity calibrated spectra from a hollow cathode discharge lamp, recorded with a Fourier transform spectrometer. Results. We report lifetimes for 13 levels at an energy around 73 000 cm(-1). Absolute transition probabilities of 78 lines are derived by combining the lifetimes and branching fractions. The experimental values are compared with theoretical data from the literature.

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  • 37.
    Nilsson, H.
    et al.
    Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Engström, L.
    Department of Physics, Lund University, Box 118, 22100 Lund, Sweden.
    Lundberg, H.
    Department of Physics, Lund University, Box 118, 22100 Lund, Sweden.
    Hartman, H.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden.
    Palmeri, P.
    Physique Atomique et Astrophysique, Université de Mons, 7000 Mons, Belgium.
    Quinet, P.
    Physique Atomique et Astrophysique, Université de Mons, 7000 Mons, Belgium; IPNAS, Université de Liège, 4000 Liège, Belgium.
    Experimental and theoretical lifetimes and transition probabilities for spectral lines in Nb II2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 627, article id A102Article in journal (Refereed)
    Abstract [en]

    Aims. We have measured and calculated lifetimes of high lying levels in Nb II, and derived absolute transition probabilities by combining the lifetimes with experimental branching fractions. Methods. The lifetimes were measured using time-resolved laser-induced fluorescence in a two-photon and two-step excitation scheme. The branching fractions were measured in intensity calibrated spectra from a hollow cathode discharge, recorded with a Fourier transform spectrometer. The calculations were performed with the relativistic Hartree-Fock method including core polarization. Results. We report experimental lifetimes of 13 levels in the 4d(3)(F-4)5d and 4d(3)(F-4)6s subconfigurations, at an energy around 70 000 cm(-1). By combining the lifetimes with experimental branching fractions absolute transition probabilities of 59 lines are derived. The experimental results are compared with calculated values.

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  • 38.
    Nilsson, H.
    et al.
    Lund Observatory, Lund University, P.O. Box 43, 22100, Lund, Sweden.
    Engström, L.
    Department of Physics, Lund Institute of Technology, P.O. Box 118, 22100, Lund, Sweden.
    Lundberg, H.
    Department of Physics, Lund Institute of Technology, P.O. Box 118, 22100, Lund, Sweden.
    Palmeri, P.
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, 20 Place du Parc, 7000, Mons, Belgium.
    Fivet, V.
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, 20 Place du Parc, 7000, Mons, Belgium.
    Quinet, P.
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, 20 Place du Parc, 7000, Mons, Belgium; IPNAS (Bâtiment B15), Université de Liège, Sart-Tilman, 4000, Liège 1, Belgium.
    Biémont, É.
    Astrophysique et Spectroscopie, Université de Mons-Hainaut, 20 Place du Parc, 7000, Mons, Belgium; IPNAS (Bâtiment B15), Université de Liège, Sart-Tilman, 4000, Liège 1, Belgium.
    Lifetime measurements and transition probability calculations in singly ionized tungsten (WII)2008In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 49, no 1, p. 13-19Article in journal (Refereed)
    Abstract [en]

    New measurements of radiative lifetimes for 9 levels in singly ionized tungsten (WII) have been performed with the time-resolved laser-induced-fluorescence technique. Transition probabilities have been obtained from a combination of experimental lifetimes and theoretical branching fractions. The reliability of the present results is assessed through the good agreement observed between the calculated lifetimes and the experimental values from this work and from previous publications. These new results fill in a gap in the available data for this atomic species particularly important for fusion reactors. 

  • 39.
    Nilsson, H.
    et al.
    Lund Observatory, Lund University, Box 43, 221 00 Lund, Sweden.
    Hartman, H.
    Lund Observatory, Lund University, Box 43, 221 00 Lund, Sweden.
    Engström, L.
    Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden.
    Lundberg, H.
    Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden.
    Sneden, C.
    Department of Astronomy, University of Texas, RLM 15.308, Austin TX78712, USA.
    Fivet, V.
    Astrophysique et Spectroscopie, Université de Mons, 20 Place du Parc, 7000 Mons, Belgium.
    Palmeri, P.
    Astrophysique et Spectroscopie, Université de Mons, 20 Place du Parc, 7000 Mons, Belgium.
    Quinet, P.
    Astrophysique et Spectroscopie, Université de Mons, 20 Place du Parc, 7000 Mons, Belgium; IPNAS, Bât. B15, Université de Liège, Sart Tilman, 4000 Liège, Belgium.
    Biémont, É.
    Astrophysique et Spectroscopie, Université de Mons, 20 Place du Parc, 7000 Mons, Belgium; IPNAS, Bât. B15, Université de Liège, Sart Tilman, 4000 Liège, Belgium.
    Transition probabilities of astrophysical interest in the niobium ions Nb+ and Nb2+2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 511, article id A16Article in journal (Refereed)
    Abstract [en]

    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.

  • 40.
    Nilsson, H.
    et al.
    Atomic Astrophysics, Lund Observatory, Box 43, 221 00 Lund.
    Ivarsson, S.
    Atomic Astrophysics, Lund Observatory, Box 43, 221 00 Lund.
    Experimental oscillator strengths and hyperfine constants in Nb ii2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 492, no 2, p. 609-616Article in journal (Refereed)
    Abstract [en]

    We used high-resolution Fourier transform spectroscopy to measure new and improved transition probabilities and hyperfine data for singly ionized niobium. Intensity calibrated spectra were used to measure branching fractions of 145 Nb II lines in the wavelength interval 2600–4600 Å. Combining the branching fractions with previously reported lifetimes, absolute oscillator strengths for these 145 transitions were derived. In addition, line structures due to magnetic hyperfine interaction were studied resulting in new hyperfine splitting constants for 28 even and 24 odd energy levels.


     

  • 41.
    Nilsson, H.
    et al.
    Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden.
    Ivarsson, S.
    Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden.
    Johansson, S.
    Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden.
    Lundberg, H.
    Department of Physics, Lund Institute of Technology, PO Box 118, 22100 Lund.
    Experimental oscillator strengths in U II of cosmological interest2002In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 381, no 3, p. 1090-1093Article in journal (Refereed)
    Abstract [en]

    Oscillator strengths for 57 U II lines in the region 3500–6700 Å  have been derived by combining new branching fraction measurements with recently measured lifetimes. The lines combine six upper levels with numerous low levels having excitation energies of 0–1.5 eV. The data include the U II line at 3859 Å, which is used for cosmochronology.

     

  • 42.
    Nilsson, H.
    et al.
    Atomic Astrophysics, Lund Observatory, Lund University, Box 43, Lund, SE-221 00, Sweden.
    Ivarsson, S.
    Atomic Astrophysics, Lund Observatory, Lund University, Box 43, Lund, SE-221 00, Sweden.
    Sabel, H.
    Atomic Astrophysics, Lund Observatory, Lund University, Box 43, Lund, SE-221 00, Sweden.
    Sikström, C. M.
    Atomic Astrophysics, Lund Observatory, Lund University, Box 43, Lund, SE-221 00, Sweden.
    Curtis, L. J.
    Department of Physics and Astronomy, University of Toledo, 43606, Ohio, USA.
    Measurements of Transition Probabilities for Complex Ions2003In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T105, no 1, p. 61-61Article in journal (Refereed)
    Abstract [en]

    Fourier transform spectroscopy has proven to be a useful tool when measuring wavelengths and branching fractions. The high spectral resolution makes it possible to extend and improve term analyses of complex spectra. We present an overview of our measurements with the Fourier transform spectrometer at Lund Observatory. Much of our work is motivated by astrophysical problems, and we show an application of some of our measurements related to the age determination of the Galaxy.

  • 43.
    Nilsson, H.
    et al.
    Atomic Astrophysics, Lund Observatory, Lund University, Box 43, 221 00 Lund, Sweden.
    Ljung, G.
    Atomic Astrophysics, Lund Observatory, Lund University, Box 43, 221 00 Lund, Sweden.
    Lundberg, H.
    Atomic Physics, Department of Physics, Lund Institute of Technology, Box 118, 221 00 Lund, Sweden.
    Nielsen, K. E.
    Catholic University of America, Washington, DC 20064, USA; Exploration of the Universe Division, Code 667, Goddard Space Flight Center, Greenbelt, MD 20771, USA.
    The FERRUM project: improved experimental oscillator strengths in Cr II2006In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 445, no 3, p. 1165-1168Article in journal (Refereed)
    Abstract [en]

    We report absolute oscillator strengths for 119   transitions in the wavelength region 2050-4850 Å. The transition probabilities have been derived by combining radiative lifetimes, measured with time-resolved laser induced fluorescence, and branching fractions from intensity calibrated Fouirer transform spectrometer data. New radiative lifetimes for the 3d4(5D)4p 4F, 4D and 6P terms are reported, adding up to a total of 25 energy levels with measured lifetimes used to derive this improved set of atomic data.


     

  • 44.
    Nilsson, H.
    et al.
    Atomic Astrophysics, Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden.
    Zhang, Z. G.
    Atomic Physics, Department of Physics, Lund Institute of Technology, PO Box 118, 22100 Lund, Sweden.
    Lundberg, H.
    Atomic Physics, Department of Physics, Lund Institute of Technology, PO Box 118, 22100 Lund, Sweden.
    Johansson, S.
    Atomic Astrophysics, Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden.
    Nordström, B.
    Atomic Astrophysics, Lund Observatory, Lund University, PO Box 43, 22100 Lund, Sweden; Niels Bohr Institute for Astronomy, Physics & Geophysics, Juliane Marie vej 30, 2100 Copenhagen, Denmark.
    Experimental oscillator strengths in Th II2002In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 382, no 1, p. 368-377Article in journal (Refereed)
    Abstract [en]

    We have measured radiative lifetimes of ten Th II levels by using the laser-induced fluorescence technique and branching fractions with Fourier transform spectroscopy. By combining the new branching fractions with a total of 23 lifetimes, from the present work and from measurements by Simonsen et al. ([CITE]), absolute oscillator strengths for 180 lines have been derived. Some of these new f-values reported are relevant for radioactive dating of stars.

     

  • 45.
    Nilsson, Hampus
    Atomic Astrophysics, Lund Observatory, Lund University Box 43, SE-221 00 Lund, Sweden.
    Infrared laboratory spectroscopy with astrophysical applications2009In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T134, p. 014009-014009Article in journal (Refereed)
    Abstract [en]

    The infrared (IR) atomic spectral lines that can be observed in laboratory and astrophysical spectra depend both on the atomic structure and the physical conditions in which the atoms reside. This is a brief review of IR laboratory spectroscopy, discussing which lines in the wavelength interval 1–5 μm can be expected to be seen in different astrophysical sources.

  • 46.
    Nilsson, Hampus
    et al.
    Atomic Astrophysics, Lund Observatory, Lund University, Box 43, Lund, SE-221 00, Sweden.
    Pickering, Juliet C
    Blackett Laboratory, Imperial College, London, SW7 2BZ, UK.
    Extended Term Analysis of Mo II2003In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 67, no 3, p. 223-233Article in journal (Refereed)
    Abstract [en]

    The spectrum of singly ionized molybdenum has been recorded with Fourier transform spectrometers in the wavelength interval 1500–7000 Å. We report improved energy values for a total of 330 levels, 153 even and 177 odd, which belong to the 4d5, 4d45s, 4d35s2, 4d46s, 4d45d, 4d45p and 4d35s5p configurations. 110 of the levels have been found in the present analysis. We have also present calculated eigenvector components and oscillator strengths.

  • 47.
    Pallé, P L
    et al.
    Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain; Department de Astrofísica, Universidad de la Laguna, E-38206 La Laguna, Tenerife, Spain.
    Grundahl, F
    Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark.
    Hage, A Triviño
    Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain; Department de Astrofísica, Universidad de la Laguna, E-38206 La Laguna, Tenerife, Spain.
    Christensen-Dalsgaard, J
    Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark.
    Frandsen, S
    Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark.
    García, R A
    Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, CEA, F-91191, Gif-sur-Yvette, France.
    Uytterhoeven, K
    Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain; Department de Astrofísica, Universidad de la Laguna, E-38206 La Laguna, Tenerife, Spain.
    Andersen, M F
    Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark.
    Rasmussen, P K
    Niels Bohr Institute, University of Copenhagen, Kbenhavn Ø, 2100, Juliane Maries Vej 30, Denmark.
    Sørensen, A N
    Niels Bohr Institute, University of Copenhagen, Kbenhavn Ø, 2100, Juliane Maries Vej 30, Denmark.
    Kjeldsen, H
    Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark.
    Spano, P
    INAF, Osservatorio Astronomico di Brera, Italy.
    Nilsson, H
    Lund Observatory, Lund University, SE-221 00 Lund, Box 43, Sweden.
    Hartman, H
    Lund Observatory, Lund University, SE-221 00 Lund, Box 43, Sweden.
    Jørgensen, U G
    Niels Bohr Institute, University of Copenhagen, Kbenhavn Ø, 2100, Juliane Maries Vej 30, Denmark; Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, København K, 1350, Øster Voldgade 5-7, Denmark.
    Skottfelt, J
    Niels Bohr Institute, University of Copenhagen, Kbenhavn Ø, 2100, Juliane Maries Vej 30, Denmark; Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, København K, 1350, Øster Voldgade 5-7, Denmark.
    Harpsøe, K
    Niels Bohr Institute, University of Copenhagen, Kbenhavn Ø, 2100, Juliane Maries Vej 30, Denmark; Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, København K, 1350, Øster Voldgade 5-7, Denmark.
    Andersen, M I
    Niels Bohr Institute, University of Copenhagen, Kbenhavn Ø, 2100, Juliane Maries Vej 30, Denmark.
    Observations of the radial velocity of the Sun as measured with the novel SONG spectrograph: results from a 1-week campaign2013In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 440, p. 012051-012051Article in journal (Refereed)
    Abstract [en]

    Deployment of the prototype node of the SONG project took place in April 2012 at Observatorio del Teide (Canary Islands). Its key instrument (echelle spectrograph) was installed and operational a few weeks later while its 1 m feeding telescope suffered a considerable delay to meet the required specifications. Using a fibre-feed, solar light could be fed to the spectrograph and we carried out a 1-week observing campaign in June 2012 to evaluate its performance for measuring precision radial velocities. In this work we present the first results of this campaign by comparing the sensitivity of the SONG spectrograph with other helioseismology reference instruments (Mark-I and GOLF) when simultaneous data are considered.

  • 48.
    Palmeri, P
    et al.
    Astrophysique et Spectroscopie, Université de Mons, 20 Place du Parc, B-7000 Mons, Belgium; IPNAS, Université de Liège, B15 Sart Tilman, B-4000 Liège, Belgium.
    Quinet, P
    Astrophysique et Spectroscopie, Université de Mons, 20 Place du Parc, B-7000 Mons, Belgium; IPNAS, Université de Liège, B15 Sart Tilman, B-4000 Liège, Belgium.
    Fivet, V
    Astrophysique et Spectroscopie, Université de Mons, 20 Place du Parc, B-7000 Mons, Belgium.
    Biémont, É
    Astrophysique et Spectroscopie, Université de Mons, 20 Place du Parc, B-7000 Mons, Belgium; IPNAS, Université de Liège, B15 Sart Tilman, B-4000 Liège, Belgium.
    Cowley, C R
    Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1090, USA.
    Engström, L
    Department of Physics, Lund Institute of Technology, PO Box 118, SE-221 00 Lund, Sweden.
    Lundberg, H
    Department of Physics, Lund Institute of Technology, PO Box 118, SE-221 00 Lund, Sweden.
    Hartman, H
    Lund Observatory, Lund University, PO Box 43, SE-221 00 Lund, Sweden.
    Nilsson, H
    Lund Observatory, Lund University, PO Box 43, SE-221 00 Lund, Sweden.
    Lifetime measurements in Ru II and calculated oscillator strengths in Ru II and Ru III2009In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 16, p. 165005-165005Article in journal (Refereed)
    Abstract [en]

    A new set of theoretical f-values is reported for 178 Ru II transitions of astrophysical interest, involving energy levels below 58 000 cm−1. The theoretical model, including core-polarization effects, has been tested by comparing theoretical lifetimes with new measurements performed by time-resolved laser-induced fluorescence spectroscopy for 23 4d6(5D)5p odd levels of Ru II and by comparing theoretical and experimental Landé g-factors. The first set of transition probabilities is proposed for 25 strong lines depopulating the 4d55p5,7P° terms of Ru III. The new results will allow quantitative investigations of stellar spectra and allow the astrophysicists to refine the ruthenium abundance in stars.

  • 49.
    Palmeri, Patrick
    et al.
    IPNAS, Université de Liège, Campus du Sart-Tilman, B-4000 Liège, Belgium.
    Quinet, Pascal
    IPNAS, Université de Liège, Campus du Sart-Tilman, B-4000 Liège, Belgium; IPNAS, Université de Liège, Campus du Sart-Tilman, B-4000 Liège, Belgium.
    Lundberg, Hans
    Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Engström, Lars
    Department of Physics, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Nilsson, Hampus
    Lund Observatory, Lund University, Box 43, SE-221 00 Lund, Sweden.
    Hartman, Henrik
    Malmö högskola, Faculty of Technology and Society (TS). Lund Observatory, Lund University, Box 43, SE-221 00 Lund, Sweden.
    Lifetime measurements using two-step laser excitation for high-lying even-parity levels and improved theoretical oscillator strengths in Y II2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 471, no 1, p. 532-540Article in journal (Refereed)
    Abstract [en]

    We report new time-resolved laser-induced fluorescence lifetime measurements for 22 highly excited even-parity levels in singly ionized yttrium (Y II). To populate these levels belonging to the configurations 4d6s, 5s6s 4d5d, 5p2, 4d7s and 4d6d, a two-step laser excitation technique was used. Our previous pseudo-relativistic Hartree–Fock model (Bi´emont et al. 2011) was improved by extending the configuration interaction up to n = 10 to reproduce the new experimental lifetimes. A set of semi-empirical oscillator strengths extended to transitions falling in the spectral range λλ194–3995 nm, depopulating these 22 even-parity levels in Y II, is presented and compared to the values found in the Kurucz’s data base (Kurucz 2011).

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  • 50.
    Pehlivan, Asli
    et al.
    Malmö högskola, Faculty of Technology and Society (TS). Lund Observatory, Box 43, 221 00 Lund, Sweden.
    Nilsson, Hampus
    Lund Observatory, Box 43, 221 00 Lund, Sweden.
    Hartman, Henrik
    Malmö högskola, Faculty of Technology and Society (TS). Lund Observatory, Box 43, 221 00 Lund, Sweden.
    Laboratory oscillator strengths of Sc i in the near-infrared region for astrophysical applications2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 582, no A98, article id A98Article in journal (Refereed)
    Abstract [en]

    Context. Atomic data is crucial for astrophysical investigations. To understand the formation and evolution of stars, we need to analyse their observed spectra. Analysing a spectrum of a star requires information about the properties of atomic lines, such as wavelengths and oscillator strengths. However, atomic data of some elements are scarce, particularly in the infrared region, and this paper is part of an effort to improve the situation on near-IR atomic data. Aims. This paper investigates the spectrum of neutral scandium, Sc i, from laboratory measurements and improves the atomic data of Sc i lines in the infrared region covering lines in R, I, J, and K bands. Especially, we focus on measuring oscillator strengths for Sc i lines connecting the levels with 4p and 4s configurations. Methods. We combined experimental branching fractions with radiative lifetimes from the literature to derive oscillator strengths (f -values). Intensity-calibrated spectra with high spectral resolution were recorded with Fourier transform spectrometer from a hollow cathode discharge lamp. The spectra were used to derive accurate oscillator strengths and wavelengths for Sc i lines, with emphasis on the infrared region. Results. This project provides the first set of experimental Sc i lines in the near-infrared region for accurate spectral analysis of astronomical objects. We derived 63 log(g f ) values for the lines between 5300 Å and 24 300 Å. The uncertainties in the f -values vary from 5% to 20%. The small uncertainties in our values allow for an increased accuracy in astrophysical abundance determinations

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    FULLTEXT01
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