Abstract
view Abstract Citations (10) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Doppler measurement with low scattered light of the higher rotation rate of sunspot magnetic fields at the photosphere. Foukal, P. Abstract We have measured the wavelength differences between two lines of Fe I and Ti I formed in sunspot umbrae, and two reference lines of N I and Na I, formed in the photosphere outside these spots. From repeated observations of 10 spots, we find that in the eastern hemisphere, the umbral lines are increasingly blueshifted relative to the photospheric lines with increasing distance from the central meridian. In the west, they show an increasing relative redshift. The Doppler shift behavior caused by steady velocity fields around sunspots, and other possible sources of systematic error, are considered in detail. The observed change of sign of the relative Doppler shift at the central meridian indicates that the umbral plasma and the magnetic flux tubes are rotating faster than the local photosphere. The mean value of the increased rotation speed over the latitude range 120 degrees, derived from the 10 spots studied in 1978, is Av = 148 + 31 ms-1. Light scattered in the coronagraph optical system and atmosphere during these observations is very small, and, in any case, would tend to reduce the value ofAVfound in this differential Doppler measurement. Thus these results demonstrate that the higher rotation rate of sunspots (and presumably of other rapidly rotating tracers) is not an instrumental effect. This measurement also shows that the higher rotation rate is the result of a systematic translation of magnetic flux tubes through the local photosphere. Subject headings: Sun: magnetic fields - Sun: rotation - Sun: sunspots Publication: The Astrophysical Journal Pub Date: December 1979 DOI: 10.1086/157548 Bibcode: 1979ApJ...234..716F Keywords: Angular Velocity; Light Scattering; Photosphere; Solar Magnetic Field; Solar Rotation; Sunspots; Coronagraphs; Doppler Effect; Frequency Shift; Plasma Diagnostics; Red Shift; Spectroheliographs; Velocity Measurement; Solar Physics; Magnetic Fields:Sunspots; Rotation:Solar Magnetic Fields; Rotation:Sunspots; Solar Rotation:Sunspots full text sources ADS |
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