Physical realism in the analysis of stellar magnetic fields

The detection and analysis of magnetic fields on cool stars have been reexamined using improved theoretical and observational methods. Lines in the near-infrared are employed which are both accessible at high signal-to-noise and resolution with CCD detectors, and more sensitive to Zeeman broadening than optical lines. The analysis of these is treated with a model atmosphere code which includes all relevant line and stellar physics (in LTE) instead of the approximate treatment of transfer that has been previously used. The possibility that observed broadenings could be due to deficiencies in past or present methods of analysis is carefully examined, and it is concluded that magnetic fields are really being detected. In particular, for Epsilon Eri an average field strength of 1000 G covering 35 percent of the stellar surface is derived and for Boo A a field of 1200 G covering 40 percent of the surface is derived. The analysis of fields from observations of spectral line profiles is discussed in detail, and some future improvements which could be made in it are mentioned.