Anna Aret Research associate Tartu Observatory Department of Astrophysics Group of Theoretical Astrophysics

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Contact:

Tartu Observatory
61602 Tõravere
ESTONIA

Phone: +372 7410 465
Fax: +372 7410 205
e-mail:

Research:

I am studying the formation of chemical peculiarities in the atmospheres of chemically peculiar (CP) stars due to diffusion and drift processes. My research involves computer simulations of the formation and evolution of peculiarities of heavy elements and their isotopes in the atmospheres of mercury-manganese (HgMn) stars.

Chemical composition of chemically peculiar (CP) stars differs drastically from other main sequence stars. It is generally believed that the abundance and isotopic anomalies observed for various elements in CP stars are the result of diffusion processes in upper layers of quiescent stellar atmospheres with almost no stellar wind, turbulence and meridional circulation. Diffusive separation is mainly determined by interplay between gravity and radiative force due to absorption of the radiative flux in spectral lines. Diffusion theory was first advanced by G. Michaud in 1970. Generally the diffusion theory explains satisfactorily observed anomalous chemical compositions but during recent years many observers have pointed that isotopic anomalies observed in CP stars are difficult to explain by diffusion theory alone.

In 1988 Russian physicists Atutov and Shalagin suggested that light-induced drift (LID) can be in many cases more efficient for generating abundance anomalies than the usual radiative acceleration. With Prof Arved Sapar we have generalized the theory of LID and applied it to element diffusion in stellar atmospheres. Together with Arved Sapar and Raivo Poolamäe we have elaborated a software package SMART to compute stellar spectra at very high resolution, the radiative field in stellar atmospheres and radiative acceleration of stellar matter which is both in thermal and turbulent motion. This software also allowes to calculate accelerations and diffusion velocities of various elements and their isotopes due to both the usual radiative acceleration in spectral lines and the light-induced drift (LID).

Calculations carried out for radiative-driven diffusion of mercury isotopes confirm the essential role of LID for element segregation in the atmospheres of CP stars and especially for isotope segregation. LID causes sequential sedimentation of lighter and levitation of heavier isotopes.

Some links:

• IAU Working Group on Ap and Related Stars
• A peculiar Newsletter
• Intel Fortran Compiler for Linux
• Fortran Open Directory
• Open Source compilers for Fortran95: GNU Fortran, G95
• High Performance Computing Projects at Liverpool University

Last modified: Fri Jul 30 10:54:46 EEST 2010 Anna Aret,