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Fig. 3


Acoustic cut-off frequency ωc as a function of height from the photosphere. Below 500 km, ωc is obtained using model S and Eq. (11); the density scale height is obtained after smoothing the density. Above 500 km, the acoustic cut-off frequency is constant and equal to ωt = 5.3 mHz. Near − 200 km, ωc is complex, although is always positive and only enters the wave equation.

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