Sunspot Magnetic Fields Measured up to 6000 Gauss
Abstract
Photoelectric `magnetographs' underestimate field strength in sunspot umbrae because of scattered light. Two techniques that do work are photographic spectra or visual observations where the Zeeman sigma components are matched by the observer with the Hale-Nicholson tipping plate and the plate angle is converted to gauss. We study field measures of 32000 spots, 1917 to 2004, from the archives of Mt. Wilson, Potsdam, Rome, and the Crimea. We find 58 spot groups with fields of 4000 G or more. A careful look at the time history of equipment used at Mt. Wilson reveals that the non-linearity of the glass plate at large tilt angles was not taken properly into account, perhaps because of their rarity. When we correct the Mt. Wilson values for strong fields we find several cases of 5000 G and one of 6100 G. Often such strong fields are associated with light bridges, but not always.
- Publication:
-
IAU Joint Discussion
- Pub Date:
- August 2006
- Bibcode:
- 2006IAUJD...3E..54L