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| roAp | Lambda Bootis | Solar type stars | Doppler Imaging |
The Solar Type Stars
In an attempt to model the observed pulsation modes of eta Boo, radial frequencies in the adiabatic approximation were computed. Also the full non-adiabatic pulsation equations were solved including the Lagrangian perturbations of the convective heat and momentum flux. Adiabatic frequency shifts of up to 15 microHz were found (Christensen-Dalsgaard et al. 1995) after inclusion of the turbulent pressure in the model .Amplitude ratios and phase relations between the luminosity and velocity of radial p modes as a function of frequency and height in the solar atmosphere were investigated as part of a PhD Thesis by G. Houdek on solar type pulsation. Recent investigations have increased evidence that solar acoustic modes are intrinsically stable and stochastically excited by turbulent convection (e.g., Houdek et al. 1995).
The height dependence of the phase shift between temperature and velocity fluctuations are compared with measurements derived from temporal line-profile variations formed at different heights in the solar atmosphere (Alamanni et al., Staiger et al.). The relative velocity phase and velocity amplitude as function of height in connection with observations were also discussed. The inclusion of convective heat and momentum flux perturbations and a consistent treatment of the radiation field is necessary to calculate more realistic amplitudes and eigenfunctions of solarlike oscillations.
The consequences of interpolation in opacity tables on model results were also investigated. Since the opacity calculation is far too complicated to be performed within stellar evolution programmes, the opacity has to be interpolated in precomputed tables. In this survey, we considered three interpolation schemes by Cline (1974), Späth (1991) and Montefusco & Casciola (1989) respectively. In regions where radiation contributes to the total flux and coincides with the opacity changes, the differences in the temperature gradient are in the order of 1 % for the solar case and larger than 4 % for the 1.5 solar mass star. The resulting changes in the velocity of sound for the 1.5 solar mass star are in the order of up to 2 % and less than 0.1 % for the Sun. However the impact on the nonadiabatic frequencies might be more severe, since nonadiabaticity is also confined in a small domain in the upper part of the convection zone. New opacity tables and interpolation routines were also integrated in the CESAM code.