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Very high resolution ultraviolet spectroscopy of a chemically peculiar star: Results of the chi Lupi Pathfinder project

Leckrone, DS; Proffitt, CR; Wahlgren, Glenn LU ; Johansson, Sveneric LU and Brage, Tomas LU (1999) In Astronomical Journal 117(3). p.1454-1470
Abstract
We summarize here the results of a major eight-year investigation of the extraordinarily detailed UV spectrum of the sharp-lined, nonmagnetic, main-sequence, chemically peculiar star chi Lupi (B9.5p HgMn + A2 Vm). The UV observations are composed of 345 Angstrom of the spectrum acquired with the Goddard High Resolution Spectrograph (GHRS) on board the Hubble Space Telescope at an average resolution of 0.023 Angstrom. The complete set of echelle spectrograms is presented as an atlas in a companion paper. These data were supplemented by optical-wavelength spectra obtained at the Angle-Australian Telescope. Quantitatively accurate analysis and theoretical interpretation of these data required major improvements in the accuracy and... (More)
We summarize here the results of a major eight-year investigation of the extraordinarily detailed UV spectrum of the sharp-lined, nonmagnetic, main-sequence, chemically peculiar star chi Lupi (B9.5p HgMn + A2 Vm). The UV observations are composed of 345 Angstrom of the spectrum acquired with the Goddard High Resolution Spectrograph (GHRS) on board the Hubble Space Telescope at an average resolution of 0.023 Angstrom. The complete set of echelle spectrograms is presented as an atlas in a companion paper. These data were supplemented by optical-wavelength spectra obtained at the Angle-Australian Telescope. Quantitatively accurate analysis and theoretical interpretation of these data required major improvements in the accuracy and completeness of available atomic data-wavelengths, transition probabilities, hyperfine structure, and isotope shifts-for the lowest ionization states of many elements. A large, international group of theoretical and experimental atomic physicists has collaborated in this investigation, and their results are summarized or referenced in this paper. In turn, the GHRS observations of chi Lupi have become a useful source of data for atomic spectroscopy, displaying many transitions that are difficult to observe in a laboratory setting. Measured abundances or upper limits are presented for 72 ions of 51 chemical elements, spanning the periodic table. We have confirmed and refined previously identified isotopic abundance anomalies in mercury and platinum and have discovered similar isotopic anomalies in thallium and, tentatively, in lead. Large discrepancies among the LTE abundances derived, using a chemically homogeneous model atmosphere, from two or three ionization states of the same element are found to be common. In some cases these are due to departures from LTE in the ionization equilibria, but the largest such discrepancies probably result from chemical stratification within the photosphere. We find qualitative trends in the abundances of the elements that clearly signify radiatively driven diffusion and gravitational settling as the primary mechanism producing abundance anomalies. However, detailed non-LTE diffusion calculations for mercury and thallium show that there is insufficient unsaturated radiative force within the chemically enriched atmosphere to sustain the observed huge overabundances of these elements in equilibrium with gravity. Either other hydrodynamic processes, such as slow mass motions or unexpectedly strong stellar winds must assist radiation pressure in supporting the enriched material, or the observed abundance patterns simply provide a snapshot in time of a nonequilibrium, time-variable phenomenon. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
physical data and processes, stars : abundances, stars : chemically, peculiar, stars : individual (chi Lupi)
in
Astronomical Journal
volume
117
issue
3
pages
1454 - 1470
publisher
The American Astronomical Society
external identifiers
  • wos:000079786900031
ISSN
1538-3881
DOI
10.1086/300776
language
English
LU publication?
yes
id
d432d3ca-5355-4261-9e59-7bb05fbafd0a (old id 3919460)
date added to LUP
2013-07-09 08:02:17
date last changed
2016-04-15 20:00:31
@article{d432d3ca-5355-4261-9e59-7bb05fbafd0a,
  abstract     = {We summarize here the results of a major eight-year investigation of the extraordinarily detailed UV spectrum of the sharp-lined, nonmagnetic, main-sequence, chemically peculiar star chi Lupi (B9.5p HgMn + A2 Vm). The UV observations are composed of 345 Angstrom of the spectrum acquired with the Goddard High Resolution Spectrograph (GHRS) on board the Hubble Space Telescope at an average resolution of 0.023 Angstrom. The complete set of echelle spectrograms is presented as an atlas in a companion paper. These data were supplemented by optical-wavelength spectra obtained at the Angle-Australian Telescope. Quantitatively accurate analysis and theoretical interpretation of these data required major improvements in the accuracy and completeness of available atomic data-wavelengths, transition probabilities, hyperfine structure, and isotope shifts-for the lowest ionization states of many elements. A large, international group of theoretical and experimental atomic physicists has collaborated in this investigation, and their results are summarized or referenced in this paper. In turn, the GHRS observations of chi Lupi have become a useful source of data for atomic spectroscopy, displaying many transitions that are difficult to observe in a laboratory setting. Measured abundances or upper limits are presented for 72 ions of 51 chemical elements, spanning the periodic table. We have confirmed and refined previously identified isotopic abundance anomalies in mercury and platinum and have discovered similar isotopic anomalies in thallium and, tentatively, in lead. Large discrepancies among the LTE abundances derived, using a chemically homogeneous model atmosphere, from two or three ionization states of the same element are found to be common. In some cases these are due to departures from LTE in the ionization equilibria, but the largest such discrepancies probably result from chemical stratification within the photosphere. We find qualitative trends in the abundances of the elements that clearly signify radiatively driven diffusion and gravitational settling as the primary mechanism producing abundance anomalies. However, detailed non-LTE diffusion calculations for mercury and thallium show that there is insufficient unsaturated radiative force within the chemically enriched atmosphere to sustain the observed huge overabundances of these elements in equilibrium with gravity. Either other hydrodynamic processes, such as slow mass motions or unexpectedly strong stellar winds must assist radiation pressure in supporting the enriched material, or the observed abundance patterns simply provide a snapshot in time of a nonequilibrium, time-variable phenomenon.},
  author       = {Leckrone, DS and Proffitt, CR and Wahlgren, Glenn and Johansson, Sveneric and Brage, Tomas},
  issn         = {1538-3881},
  keyword      = {physical data and processes,stars : abundances,stars : chemically,peculiar,stars : individual (chi Lupi)},
  language     = {eng},
  number       = {3},
  pages        = {1454--1470},
  publisher    = {The American Astronomical Society},
  series       = {Astronomical Journal},
  title        = {Very high resolution ultraviolet spectroscopy of a chemically peculiar star: Results of the chi Lupi Pathfinder project},
  url          = {http://dx.doi.org/10.1086/300776},
  volume       = {117},
  year         = {1999},
}