Abstract
Direct measurement of intensity and photographic subtractions of simultaneous Doppler filtergrams at Hα±0.3 Å in a time-lapse sequence of McMath 11482 has shown velocity oscillations in sunspot umbrae. These oscillations exhibit the following characteristics: (a) A characteristic oscillation frequency for each umbra, with the periods ranging from 145±10 s to 180±10 s. (b) A duration of at least 8 cycles. (c) A Doppler shift of 10 km s-1. (d) An oscillating element size of 3″ or less. (e) A visibility to a radius vector of about 0.9.
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Phillis, G.L. Hα oscillations in sunspot umbrae. Sol Phys 41, 71–79 (1975). https://doi.org/10.1007/BF00152957
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DOI: https://doi.org/10.1007/BF00152957