| 1. |
- Brage, Tomas, et al.
(författare)
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Atomic calculations inspired by the GHRS - gf-values, hyperfine structure constants, and isotope shifts for heavy elements
- 1998
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Ingår i: The Scientific Impact of the Goddard High Resolution Spectrograph (Astronomical Society of the Pacific Conference Series). - 1886733635 ; 143, s. 378-381
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Konferensbidrag (refereegranskat)abstract
- GHRS observations of chemically peculiar stars have initiated a new project for calculating atomic properties of heavy elements (Z approximate to 80). The method used is based on large-scale, fully relativistic MCDF, and the data involve accurate gf-values, hyperfine structure parameters, and relative isotope shifts.
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| 2. |
- Leckrone, DS, et al.
(författare)
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GHRS spectroscopy of chemically peculiar stars: The chi Lupi Pathfinder Project
- 1998
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Ingår i: The Scientific Impact of the Goddard High Resolution Spectrograph (Astronomical Society of the Pacific Conference Series). - 1886733635 ; 143, s. 135-153
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Konferensbidrag (refereegranskat)abstract
- The HST has provided visual images of the universe of unprecedented clarity and sensitivity. It is less widely known that the HST/GHRS has provided equally breathtaking views of a different kind Of "universe" - a "spectroscopic universe". Nowhere is this better seen than in the extraordinarily complex and beautiful ultraviolet spectrum of the ultra-sharp-lined, non-magnetic, chemically peculiar (CP) star chi Lupi (B9.5pHgMn + A2 Vm). We have begun a systematic exploration and quantitative analysis of this spectrum with the echelle mode of the GHRS. We call this the "The chi Lupi Pathfinder Project", because it is analogous to the exploration and mapping of a previously uncharted land by a diverse team of specialists - in this case astrophysicists and atomic physicists working synergistically. Our objective is to characterize, comprehensively and accurately, the full range of abundance and isotopic anomalies found in the atmosphere of at least one CP star to test and constrain the most widely accepted theoretical scenario for the production of abundance anomalies - radiatively-driven diffusion and gravitational settling. These physical mechanisms are important in several other astrophysical contexts. The surface layers of the CP stars provide a laboratory to investigate the conditions which foster them and the competing mechanisms which retard them. The GHRS echelle data set for chi Lupi covers 345 Angstrom, with S/N approximate to 50-100. We have quadrupled the number of elements for which abundances have been measured in this star, spanning most of the periodic table. These include several elements which have rarely, if ever, been seen before in a star other than the Sun and several examples of isotopically anomalous abundances. We have found systematic trends in these abundance data, which qualitatively support the mechanism of radiatively-driven diffusion and gravitational settling. However, our state-of-the-art theoretical, non-LTE diffusion models have not as yet been successful in sustaining the observed magnitudes of the largest abundance anomalies nor in reproducing anomalous isotope blends.
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| 3. |
- Proffitt, CR, et al.
(författare)
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Selections from the GHRS atlas of chi Lupi
- 1998
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Ingår i: The Scientific Impact of the Goddard High Resolution Spectrograph (Astronomical Society of the Pacific Conference Series). - 1886733635 ; 143, s. 322-325
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Konferensbidrag (refereegranskat)abstract
- High S/N echelle data of chi Lupi have been obtained at 36 different wavelength settings. The high resolution of the observations combined with the low rotational velocity of chi Lupi (v sin i approximate to 1 km s(-1)), allow the UV spectrum of this star to be seen with unprecedented detail, and provides a unique resource for the study of both atomic physics and stellar atmospheres.
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| 4. |
- Wahlgren, Glenn, et al.
(författare)
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Very heavy elements in the HgMn star chi Lupi
- 1998
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Ingår i: The Scientific Impact of the Goddard High Resolution Spectrograph (Astronomical Society of the Pacific Conference Series). - 1886733635 ; 143, s. 330-333
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Konferensbidrag (refereegranskat)abstract
- Abundances for the elements W, Os, and Bi are presented for the HgMn star chi Lupi, based upon GHRS echelle-mode spectra and a synthetic spectrum analysis. The tungsten abundance is consistent with a solar-system value while the osmium and bismuth abundances reflect enhancements. With these new data we are able to quantitatively define an abundance peak within the element range Z = 74 through 83.
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