Sunspot Vector Magnetic Fields and Model Umbral Atmospheres

摘要

The Stokes polarimeter of the High Altitude Observatory has been used to observe a round, unipolar sunspot in three absorption lines and the nearby continua. Observations in the weak Zeeman triplet at 6302.50A wavelength are used to derive the vector magnetic field across the spot. Stokes profiles are used to probe the depth variation of the magnetic field and to obtain a model atmosphere for the umbra. A linear anticorrelation is found between the continuum intensity and the magnetic field strength. Time series observations in the umbra show significant power in the field strength and continuum intensity at periods of (197 + or - 25) seconds and (266 + or - 35) seconds, respectively. A smaller, but still noteworthy, amount of power is evident in the transverse component at the (197 + or - 25) second period. Model atmospheres determined at four locations in the umbra represent a significant improvement over the few existing umbral models in fitting the observed D2 line wings. A new method of determining the longitudinal component of the B field as a function of depth is derived and tested with synthetic Stokes profiles.