MULTI-LAYER STUDY OF WAVE PROPAGATION IN SUNSPOTS

Journal Article · Sun Oct 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/722/1/131· OSTI ID:21464721

Felipe, T; Khomenko, E; Collados, M; Beck, C ^[1]

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1. Instituto de Astrofisica de Canarias, 38205 C/VIa Lactea, s/n La Laguna, Tenerife (Spain)

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 {lambda}10,827 and the He I {lambda}10,830 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 {lambda}10,830 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.

• OSTI ID: 21464721
• Journal Information: Astrophysical Journal, Vol. 722, Issue 1; Other Information: DOI: 10.1088/0004-637X/722/1/131; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CHROMOSPHERE
DOPPLER EFFECT
MAGNETIC FIELDS
MAGNETOACOUSTIC WAVES
PHOTOSPHERE
STANDING WAVES
SUN
SUNSPOTS
TIME DELAY
WAVE PROPAGATION
ATMOSPHERES
HYDROMAGNETIC WAVES
MAIN SEQUENCE STARS
SOLAR ACTIVITY
SOLAR ATMOSPHERE
STARS
STARSPOTS
STELLAR ACTIVITY
STELLAR ATMOSPHERES