Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986apj...301.1005l&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 301, Feb. 15, 1986, p. 1005-1017.
Astronomy and Astrophysics
Astrophysics
40
Abundance, Chromosphere, Electrophotometry, Solar Oscillations, Stellar Spectrophotometry, Sunspots, Calcium, Doppler Effect, Helium Ions, Hydrogen, Line Shape, Line Spectra, Temporal Distribution, Umbras
Scientific paper
Simultaneous observations of profiles of He I λ10830 and the Ca II H line in sunspot umbrae have been made with the Tower telescope, echelle spectrograph, and multidiode array at the National Solar Observatory/Sunspot. These observations reveal the nature of fluid motions in the upper chromosphere during the cycle of umbral oscillations. Time sequences of profiles show that the chromospheric He I line is in weak absorption during all phases of the umbral oscillations, and that it undergoes periodic Doppler shifts of high amplitude (up to 11 km s-1). The amplitudes and waveforms of the Doppler shifts in the He I line indicate that the oscillations are frequently nonlinear (i.e., forming shocks) and therefore contribute to the heating of the upper umbral chromosphere.
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