Seismological analysis of the second Helium ionization zone of stars

A. Miglio1,2, J. Christensen-Dalsgaard2, M.P. Di Mauro3, M.J.P.F.G. Monteiro4,5, M.J. Thompson6
1 Universitá degli Studi di Milano, Milano, Italy
2IFA, Institute for Physics and Astronomy Aarhus, Ny Munkegade Bygn. 520, DK-8000 Aarhus C, Denmark
3INAF, Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
4 Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
5 Departamento de Matematica Aplicada, Faculdade de Ciências da Universidade do Porto, Portugal.
6Space & Atmospheric Physics, The Blackett Laboratory, Imperial College, SW7 2BW London, UK

 

The region of the second ionization of Helium in the stars is a narrow subsurface layer whose thermodynamic properties are responsible for the presence of a characteristic signature in the oscillation frequencies of the p modes. Here, with the aim of detecting the acoustic depth of the second Helium ionization zone in the stars, we consider two methods of analysing the signal generated on the oscillation frequencies by the sharp decrease in the first adiabatic exponent, which occurs where ionization takes place.
The properties of the ionization zone, once determined only by seismological means, may be used to put constraints on the structure of the stars, in particular on the envelope Helium abundance.

 
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