| 1. |
- Nilsson, H, et al.
(author)
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The FERRUM project: new experimental and theoretical f-values for 4p-4d transitions in FeII applied to HST spectra of chi Lupi
- 2000
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In: Astronomy & Astrophysics. - 0004-6361. ; 362:1, s. 410-418
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Journal article (peer-reviewed)abstract
- Radiative lifetimes for six highly excited levels in Fe II have been measured at Lund Laser Centre applying the laser induced fluorescence technique and two-step excitation. The energy levels belong to the even-parity 3d(6)(D-5)(4)d subconfiguration at about 10 eV. Branching fractions (BF:s) of 29 transitions from these levels to the 3d(6)(D-5)4p subconfiguration at about 5 eV have been measured in the wavelength region 2000-3000 Angstrom with the Lund Fourier Transform Spectrometer. By normalizing the BF:s with the lifetimes we get experimental oscillator strengths for these 29 4p-4d lines. The oscillator strengths are compared with new theoretical calculations using the orthogonal operator technique and applied to high-resolution spectra of the star chi Lupi, recorded with the Hubble Space Telescope.
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| 2. |
- Sikstrom, C. M, et al.
(author)
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New Zr II oscillator strengths and the zirconium conflict in the HgMn star chi Lupi
- 1999
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In: Astronomy & Astrophysics. - 0004-6361. ; 343:1, s. 297-302
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Journal article (peer-reviewed)abstract
- Lifetimes on the sub-nanosecond scale for the levels v(2)D(3/2), v(2)F(3/2) and v(2)F(5/2) in the 4d5s5p configuration in Zr II have been measured, using the method of laser-induced fluorescence. Combined with branching fractions obtained with the Lund Ultraviolet (UV) Fourier Transform Spectrometer (FTS), experimental oscillator strengths have been derived. From Hubble Space Telescope/Goddard High-Resolution Spectrograph spectra, the zirconium abundance in the HgMn star chi Lupi has been determined from Zr II and Zr III lines. More than an order of magnitude difference in the Zr II abundance has been derived from these ionization stages. The difference is much too large to be explained by uncertainties in the oscillator strengths. Possible explanations of this difference have to be found in the stellar models, such as the influence of non-LTE or diffusion.
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| 3. |
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| 4. |
- Adelman, S J, et al.
(author)
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Heavy Element Abundances in Late-B and Early-A Stars. I. Co-Added IUE Spectra of HgMn Stars
- 2004
-
In: The Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 155:1, s. 179-189
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Journal article (peer-reviewed)abstract
- Very heavy elements (Pt, Au, Hg, Tl, and Bi) are found to be enhanced inthe atmospheres of the chemically peculiar stars of the upper mainsequence by up to a million times the solar system levels. Suchenhancements are believed to result from atmospheric dynamics (i.e.,diffusion) rather than scenarios that dredge up nuclear-processedmaterial to the surface or transfer processed material between binarycompanions. However, the theoretical framework needs to be furtherconstrained by observations beyond the realm of the spectral types forwhich such abundance enhancements are observed at optical wavelengths.The International Ultraviolet Explorer (IUE) satellite collected spectraof bright stars for which chemical peculiarities have been derived fromground-based data. For several elements the abundance enhancements haveonly been recently measured using Hubble Space Telescope data and havetherefore not yet been exploited in the IUE data. We have initiated aprogram to analyze IUE high-dispersion spectra to more fullycharacterize the pattern of very heavy element enhancement for manymercury-manganese (HgMn) stars and to potentially extend the spectralclass (effective temperature) boundaries over which these abundanceanomalies are known to exist. The abundances of very heavy elements inchemically normal B and A-type stars provide a base level that may becompared with the solar system abundances. These early spectral typestars may therefore reveal clues for galactic chemical evolution studiessince they were formed at a later epoch than the Sun in the history ofthe Galaxy. This first paper presents the motivation for the analyses tofollow, outlines our spectral co-addition technique for IUE spectra, anddiscusses the choice of model atmospheres and the synthetic spectrumprocedures, while initiating the study by highlighting the abundance ofgold in several HgMn stars.
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| 5. |
- Adelman, S. J., et al.
(author)
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Ultraviolet Spectral Analyses of HgMn Stars
- 2001
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In: Bulletin of the American Astronomical Society. ; 33:4, s. 1328-1328
-
Conference paper (peer-reviewed)abstract
- Almost a decade after the last observations were performed by theInternational Ultraviolet Explorer (IUE) satellite its rich archivescomprise a wealth of opportunity for the stellar astronomer, inparticular when exploring large samples of stars. We have inaugurated anexploration into the nature of chemically peculiar stars through thoseelemental abundance studies which are best carried out at UVwavelengths. The analysis of the IUE data set is benefited at this timeby improvements in data quality as instituted by IUE NEWSIPS and acoaddition procedure that we have implemented for those stars for whichmultiple spectral images exist in the IUE archives. The IUE dataanalysis is furthered by high resolution HST/GHRS and STIS spectraobtained for a few appropriate targets. The HST data allow for theproduction of spectral templates which can subsequently be applied tothe lower resolution IUE data in order to more fully understand lineblending issues. Our present studies are concentrated on thedistribution of heavy elements in the atmospheres of HgMn stars and willbe expanded to include other classes of chemical peculiarity in aneffort to understand the phenomenon of spectral line anomalies amongstars of the upper main sequence. We outline our techniques and presentabundance results for the poorly studied element gold in HgMn stars.This work was supported by a Grant from NASA's ADP Program.
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| 6. |
- Johansson, S. G, et al.
(author)
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Comparison of New Experimental and Astrophysical F-values For Some Ru-ii Lines, Observed In Hst Spectra of Chi-lupi
- 1994
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 421:2, s. 809-815
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Journal article (peer-reviewed)abstract
- We report on experimental absolute oscillator strengths for 18 UV lines of Ru II, obtained by combining laser-induced fluorescence measurements of radiative lifetimes and branching fractions from line intensities in a calibrated Fourier-transform spectrum. HST/GHRS observations of the spectrum of the sharp-lined B star chi Lupi contain six of these lines, for which ''astrophysical'' relative f-values have been determined. The agreement is within 0.10 dex for a Ru abundance of log N(Ru)/N(H) = -7.90, which is 2.3 dex above the solar abundance.
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| 7. |
- Lundberg, Hans, et al.
(author)
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Experimental Pd II oscillator strengths and the palladium abundance in the HgMn-type star chi Lupi
- 1996
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 469:1, s. 388-392
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Journal article (peer-reviewed)abstract
- Experimental oscillator strengths for 19 ultraviolet lines of Pd II have been derived from measurements of line intensities in calibrated Fourier transform spectra, combined with picosecond-pulse laser measurements of radiative lifetimes. Five of these 19 lines, in addition to other Pd nr lines, are present in Hubble Space Telescope/Goddard High-Resolution Spectrograph echelle spectra of the chemically peculiar HgMn star chi Lupi, yielding a palladium abundance of log (N-Pd) = +5.0, which is 3.3 dex above the solar abundance. Theoretical oscillator strengths have been calculated for all strong ultraviolet transitions associated with the lowest odd-parity configuration of Pd II.
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| 8. |
- Eriksson, Mattias, et al.
(author)
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Spectral Data for Ta II with Application to the Tantalum Abundance in chi Lupi
- 2002
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In: Physica Scripta. - 0031-8949. ; 65:6, s. 480-489
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Journal article (peer-reviewed)abstract
- Tantalum spectra, emitted from a hollow cathode, have been recorded with a Fourier transform spectrometer in the region 2000–5000 Ů The observed hyperfine patterns of Ta II have been analyzed, yielding center-of-gravity wavelengths for 199 lines and hyperfine constants for 38 even and 97 odd levels of Ta II. Improved energy level values have been derived. The laboratory data have been used for a study of the tantalum abundance of the CP star chi Lupi.
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| 9. |
- Ivarsson, Stefan, et al.
(author)
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Constraining the very heavy elemental abundance peak in the chemically peculiar star χ Lupi, with new atomic data for Os II and Ir II
- 2004
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In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 425:1, s. 353-360
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Journal article (peer-reviewed)abstract
- The determination of elemental abundances plays an important role inunderstanding the atmospheric processes that lead to anomalies inspectra of chemically peculiar stars. Ongoing study of the HgMn star χ Lupi has defined much of the elemental abundance distribution but progress is dependent upon the availability and accuracy of the atomic data. Here we present experimentally determined wavelengths and oscillator strengths for 27 Os II and 23 Ir II transitions. The oscillator strengths have been determined by combining radiative lifetimes measured using the laser-induced fluorescence technique withbranching fractions determined from Fourier transform spectrometeremission line intensities. The new data were used in a synthetic spectrum analysis of high-resolution ultraviolet spectra of χ Lupi obtained with the Hubble Space Telescope. Weak abundance enhancement swere determined for both elements, [Os/H] = +1.3 dex and [Ir/H] = +0.7dex, which now clearly defines the heavy element abundance peak in this star to be comprised of only the four elements Pt, Au, Hg, and Tl. This result offers a new constraint on theoretical efforts to explain the observed spectrum anomalies. Based in part on observations obtained with the GHRS instrument on board the Hubble Space Telescope.
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| 10. |
- Wahlgren, Glenn, et al.
(author)
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The Bismuth Abundance in the HGMN Stars chi Lupi and HR 7775 and Improved Atomic Data for Selected Transitions of BI I, BI II, and BI III
- 2001
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 551:1, s. 520-535
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Journal article (peer-reviewed)abstract
- High-resolution spectra of the chemically peculiar HgMn stars chi Lupiand HR 7775, obtained with the Hubble Space Telescope/Goddard HighResolution Spectrograph, are investigated for their abundance of bismuthby comparison with LTE synthetic spectrum modeling. HR 7775, previouslyknown from International Ultraviolet Explorer spectra to display stronglines of Bi II, is determined to have bismuth present at an enhancementlevel of nearly 5 orders of magnitude from the lines Bi IIlambdalambda1436, 1902 and Bi III lambda1423. The bismuthenhancement for chi Lupi is found to be near a level of 1.5 dex, andan ionization anomaly between Bi+ and Bi++ isapparent. HR 7775 abundance enhancements of the heavy elements platinum,[Pt/H]=4.7 dex, and gold, [Au/H]=3.8 dex, have also been determined. Newlaboratory measurements for wavelengths and hyperfine structure patternsof Bi I/Bi II/Bi III lines are presented, as well as the results ofcalculations for hyperfine structure constants and oscillator strengthsfor selected lines of Bi II and Bi III. Based on observations with theNASA/ESA Hubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS5-26555.
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