An analytic theory of adiabatic p-modes in the atmospheres of the Sun and Sun-like stars.

Details An analytic theory of adiabatic p-modes in the atmospheres of the Sun and Sun-like stars. An analytic theory of adiabatic p-modes in the atmospheres of the Sun and Sun-like stars.

Nov 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...303..561d&link_type=abstract

Astronomy and Astrophysics, v.303, p.561

Astronomy and Astrophysics

Astrophysics

7

Hydrodynamics, Sun: Atmosphere, Sun: Oscillations, Stars: Oscillations

Scientific paper

The height profile of temperature T of the solar or a stellar model, extending from the subphotosphere through the atmosphere up to the corona, has been piecewise approximated by various nonlinear and linear functions for the different regions. Solving the basic equations of adiabatic, nonvertical oscillations for these regions in the Cowling approximation we obtained the eigenfunctions for the p-modes in analytic form. Using these exact solutions it has been demonstrated, that the mechanism of resonant transmission of acoustic waves through the considered layers is sufficient to explain the main features of the observed frequency spectrum of the solar p-modes, including the 5-min oscillations and the peaks in the high-frequency tail. It has been shown that the upper turning point of the resonator for low frequencies ν<~4mHz does not coincide with the boundary of the acoustic potential barrier, the latter extending from the steep gradient of T at the upper subphotosphere up to that above the minimum of T. The wakes of the waves penetrate deep into the barrier (up to a height of 500km in the solar atmosphere) and are reflected from there. High frequencies are reflected from the chromosphere-corona transition region. For not any frequency there exists a total reflection; with increasing frequency there is an increasing leakage of wave energy into the corona. It has been shown that all observable characteristics of oscillations depend directly on the phase shift {DELTA}φ between upward and downward running waves. The resonance peaks in the spectrum arise at {DELTA}φ=0, where {DELTA}φ has been defined in the limits [-π, +π]. The dependence of the power spectrum on the height, on the frequency, and on the degree l has been demonstrated. The first resonant frequencies always correspond to the 5-min oscillations.

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