Sirvi Kuupäev , alustades "2009-05-05T08:57:33Z" järgi

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Evolutionary separation of mercury isotopes in atmospheres of chemically peculiar stars
(2009-05-05T08:57:33Z) Aret, Anna
Chemically peculiar (CP) stars are hot main-sequence stars with distinctly abnormal abundances of several elements. In addition to the element abundance anomalies, peculiar isotopic mixtures of several elements (e.g. He, Li, Hg, Pt) have been observed in many CP stars. According to the general opinion the anomalous abundances form in atmospheres of the stars, while the bulk composition of the entire star is normal. Mechanism responsible for generation of these peculiarities is radiative-driven atomic diffusion. The diffusion theory provides reliable explanation for observed abundance inhomogeneities in CP stars, but isotopic anomalies cannot be explained by radiative-driven diffusion alone. Radiation pressure is almost the same for all isotopes of an element and thus cannot cause isotope separation. However, additional effect called light-induced drift (LID) appears when radiation is absorbed in the spectral line. Magnitude and direction of LID depend on the asymmetry of the spectral line profile. This effect was discovered about 30 years ago in laser experiments and noted to be effective for isotope separation in laboratory conditions. The main objective of the present thesis is to evaluate phenomenon of light-induced drift as possible mechanism of diffusive separation of isotopes in atmospheres of CP stars. Analytical formulae, describing LID in quiescent stellar atmospheres have been derived. Software has been composed for computation of evolutionary scenarios of isotope separation due to gravity, radiative pressure and LID. Atomic and spectral data for model computations have been collected and capacious model computations have been carried out. Obtained results confirm important role of the LID in triggering and generating diffusional separation of mercury isotopes in the quiescent atmospheres of chemically peculiar stars.