Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000arep...44..202k&link_type=abstract
Astronomy Reports, Volume 44, Issue 3, March 2000, pp.202-208
Astronomy and Astrophysics
Astronomy
2
Scientific paper
Observations of oscillations in the penumbras of seven sunspots are analyzed. High-sensitivity differential measurements of the line-of-sight velocity (11 time series) and variations of the Ni I 4857 Å and Hβ line profiles (four series) have provided new data making it possible to improve estimates of the amplitude and spectral characteristics of the oscillations. In the middle penumbras, oscillations of the line-of-sight velocity with fundamental periods of 5 and 8 10 min predominate at the photospheric level; their amplitude does not exceed 40 50 m/s, and the spatial coherence scale in the radial direction is no greater than 5″ 10″. At frequencies of 0.5 2.0 mHz, the phase difference between the photosphere and chromosphere (NiI 4857 Å-Hβ) is close to 180°. The line-of-sight velocity component due to Evershed motions is responsible for oscillations with periods of 15 35 min, which occur synchronously at both heights.
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