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- Wahlgren, Glenn, et al.
(författare)
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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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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 551:1, s. 520-535
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Tidskriftsartikel (refereegranskat)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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2. |
- Adelman, S J, et al.
(författare)
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Heavy Element Abundances in Late-B and Early-A Stars. I. Co-Added IUE Spectra of HgMn Stars
- 2004
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Ingår i: The Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 155:1, s. 179-189
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Tidskriftsartikel (refereegranskat)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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3. |
- Adelman, S. J., et al.
(författare)
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Ultraviolet Spectral Analyses of HgMn Stars
- 2001
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Ingår i: Bulletin of the American Astronomical Society. ; 33:4, s. 1328-1328
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Konferensbidrag (refereegranskat)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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