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L. Rottler (UCSC, IGPP/Earth Sciences), A. Young (SDSU, Astronomy Department)
We present a study of two double-lined spectroscopic binaries selected to contain one or more chemically peculiar components of the HgMn (CP3) type. The intent is to examine specific effects expected from the radiative diffusion model that is currently the accepted explanation for the observed surface chemical anomalies. In one such system (66 Eri; P ~ 5 d) the two component stars are almost identical in their physical properties, differing in mass by no more than 5%, and in temperature by no more than 200 K, and having indistinguishable rotation velocities. In spite of such physical similarities, only one component exhibits the elevated abundances of such elements as mercury (Hg) and yttrium (Y) while the other component is devoid of such elements at our detection threshold. The radiative diffusion mechanism cannot give an accounting of such a difference between stars that have a common history of formation and virtually identical physical properties. Additionally, the component that exhibits the anomalous chemical composition appears to be devoid of the elements Mn and Pt, commonly found in the CP3 stars.
In the other binary system (46 Dra; P ~ 10 d) the component stars differ in mass by 15% and differ by 600 K in surface temperature, but both components exhibit the chemical peculiarities characterizing the HgMn (CP3) type, although not in the same abundances. In and of itself, that is not inconsistent with radiative diffusion as the driving mechanism. However, our observations reveal a different isotopic structure for the Hg II (3984 A) line in the two components which is not readily accounted for by the radiative diffusion model.
Our conclusion based upon these cases is that the radiative diffusion model cannot by itself account for the observed anomalies, and that it must be called into question as the explanation for the chemical and isotopic anomalies observed in the CP3 stars.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.