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Session 78 - Stars - Young and Old, Large and Small.
Display session, Wednesday, January 15
Metropolitan Ballroom,
Using the echelle mode of the Hubble Space Telescope/Goddard High Resolution Spectrograph, observations of the extremely sharp-lined HgMn star \chi Lupi have provided new insights into the ultraviolet spectrum, both for the purposes of astrophysics and atomic spectroscopy. Testing the diffusion paradigm, generally believed to be the dominant influence in creating the plethora of spectral line strength anomalies in HgMn stars, requires knowledge of the isotope mixture at several ionization stages. Our exciting data for the element mercury provided the impetus to expand our study to include other heavy elements.
The high quality GHRS spectra have placed stringent requirements upon the accuracy of the atomic data utilized in our synthetic spectrum analyses. Therefore, we have undertaken a concerted effort to employ both laboratory techniques and theoretical calculations in order to provide such needed data. As a result of this effort we are now able to nearly fully define quantitatively the abundance distribution in this star over the element range defined by the 5d elements tungsten (Z = 74) through mercury (Z = 80) and the 6p elements thallium (Z = 81) through bismuth (Z = 83). We present new abundance determinations for several of these elements, the result of which is to emphasize the presence of a peak in the abundance distribution, defined by the elements platinum (Z = 78) through thallium (Z = 81). This peak, with abundances four to five orders of magnitude greater than the solar system values, is present for the three lowest stages of ionization and is broader than either the r- or s-process peaks that are found in this vicinity of the periodic table in the solar system elemental abundance distribution.
