Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...415..383p&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 415, no. 1, p. 383-396.
Astronomy and Astrophysics
Astrophysics
19
Photosphere, Solar Atmosphere, Solar Oscillations, Solar Spectra, Umbras, Fourier Analysis, Spectrographs, Sunspots
Scientific paper
We observed the oscillations in the umbrae of two sunspots, using the MCCD imaging spectrograph at the Mees Solar Observatory on Haleakala, Maui. We perform four spatial analyses of the umbral velocity and find that (1) there is more power traveling toward the center of the umbrae than leaving the center of the umbrae (this provides a direct measure of the absorption of p-modes by the sunspot umbrae); (2) the umbral oscillations display power in the same spatial and temporal frequency band as the quiet-sun oscillations; (3) Fourier-Bessel analysis of one umbra shows no obvious resonant frequencies which might represent natural oscillation modes; and (4) the centers of the umbrae have less rms velocity at high spatial wavenumber than the edges of the umbrae. We conclude: (1) the photospheric umbral oscillations are driven by a source external to the sunspot, the global p-mode oscillations; (2) there are no resonant frequencies in the oscillations; and (3) the absorption of acoustic waves occurs inside the umbrae.
LaBonte Barry J.
Penn Matt J.
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