Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1975
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975mnras.172..205l&link_type=abstract
Monthly Notices of the Royal Astronomical Society, vol. 172, July 1975, p. 205-220.
Astronomy and Astrophysics
Astronomy
12
Astronomical Models, Penumbras, Solar Spectra, Sunspots, Umbras, Velocity Distribution, Iron, Line Spectra, Magnetohydrodynamic Waves, Solar Atmosphere, Spectroheliographs
Scientific paper
Line-of-sight velocity components are determined for the material in a sunspot using the Fe I 6302.499-A and 6270.231-A lines together with the Fe II 6247.562-A line. All three velocity components are constructed with the assumption that the sunspot velocity field is axisymmetric with respect to the spot's center. A very small downward velocity is found at the center of the umbra, but no such component is found anywhere else in the sunspot area. The usual radial outflow in the penumbra is detected as well as a smaller outflow in the umbra, and azimuthal velocity components are observed in both the umbra and penumbra. The velocity fields in both Fe I and Fe II are shown to be similar, indicating that both are formed in the sunspot. It is concluded that an interpretation of sunspot line shifts in terms of distortion by hydromagnetic waves may be more promising than an interpretation in terms of streaming motions.
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