Zeeman enhancement of lines in extemely active K dwarfs

We have searched for the predicted enhancement of the equivalent widths of Zeeman-sensitive lines in five chromospherically active K dwarfs, by direct comparison with inactive dwarfs of similar spectral type. In two active stars, EQ Vir and HD 82558, the equivalent widths indeed exhibit enhancements (of up to 30%) which correlate with the Zeeman sensitivity of the individual lines. HD 17925 barely shows the effect, and epsilon Eri does not show it. The amount of the Zeeman effect is related to the enhancement of the emission cores of the Ca II infrared triplet lines. Radiative transfer models including magnetic fields permit estimates of Bf, the product of field strength (B) and surface filling factor (f). Our detections imply Bf approximately equals 2kG to 3kG, in agreement with Saar. Difficulties in predicting line strengths from active stars arise due to surface inhomogeneities. These render the method ineffective in our most active case, GI 171.2.