Seismic Abundance Determination in the Sun and in Stars

Details Seismic Abundance Determination in the Sun and in Stars Seismic Abundance Determination in the Sun and in Stars

Nov 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aipc..948..179d&link_type=abstract

UNSOLVED PROBLEMS IN STELLAR PHYSICS: A Conference in Honor of Douglas Gough. AIP Conference Proceedings, Volume 948, pp. 179-1

Physics

1

Pulsations, Oscillations, And Stellar Seismology, Abundances, Chemical Composition, Stellar Structure, Interiors, Evolution, Nucleosynthesis, Ages, Solar Interior

Scientific paper

The modulation of the equation of state by the chemical composition leads to a natural helio- and asteroseismic method to determine the helium and heavy-element abundance. The idea was first proposed by Douglas Gough, who suggested to exploit the thermodynamic signature of each element. For solar helium this became indeed the only reliable method. Its result (0.24-0.25 in mass fraction) turned out to be substantial lower than the calibrated values for age-zero solar models (0.27-0.28), a discrepancy which drew renewed attention to the importance of the effect of gravitational settling of helium and heavier elements. One has to keep in mind that the result is only as good as the quality of the equation of state, and so far, there are only theoretical formalisms, but no experiments, for the relevant physical conditions. Astrophysical constraints on the quality of the equation of state, however, might come from the solar heavy-element abundance determination. For the heavy elements there are spectroscopic measurements (recently somewhat clouded in doubt though). These measurements can be used to constrain the equation of state. As a consequence, the seismic element determinations become part of a larger project, making the Sun and stars laboratories to study thermodynamic properties of Coulomb systems under conditions not (yet) achieved on Earth. In this enterprise, asteroseismology will play an important parallel role, where the lack of solar-quality data will be more than compensated by the possibility to study stars of significantly different element abundances.

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