Bibcode
Felipe, T.; Khomenko, E.; Collados, M.; Beck, C.
Referencia bibliográfica
The Astrophysical Journal, Volume 722, Issue 1, pp. 131-144 (2010).
Advertised on:
10
2010
Revista
Número de citas
85
Número de citas referidas
80
Descripción
We analyze the propagation of waves in sunspots from the photosphere to
the chromosphere using time series of co-spatial Ca II H intensity
spectra (including its line blends) and polarimetric spectra of Si I
λ10,827 and the He I λ10,830 multiplet. From the Doppler
shifts of these lines we retrieve the variation of the velocity along
the line of sight at several heights. Phase spectra are used to obtain
the relation between the oscillatory signals. Our analysis reveals
standing waves at frequencies lower than 4 mHz and a continuous
propagation of waves at higher frequencies, which steepen into shocks in
the chromosphere when approaching the formation height of the Ca II H
core. The observed nonlinearities are weaker in Ca II H than in He I
lines. Our analysis suggests that the Ca II H core forms at a lower
height than the He I λ10,830 line: a time delay of about 20 s is
measured between the Doppler signal detected at both wavelengths. We fit
a model of linear slow magnetoacoustic wave propagation in a stratified
atmosphere with radiative losses according to Newton's cooling law to
the phase spectra and derive the difference in the formation height of
the spectral lines. We show that the linear model describes well the
wave propagation up to the formation height of Ca II H, where
nonlinearities start to become very important.
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