Resumen
Observations of the Zeeman effect in OH and CN provide valuable information about magnetic field strengths and directions in molecular clouds in the density range 10(3) < n(cm(-3) ) < 10(6) that these species sample. These data make it possible to test predictions of weak field, turbulence driven star formation and strong field, ambipolar diffusion driven star formation. Here we discuss exactly what information Zeeman observations provide and how those data may be analyzed to yield meaningful results. The data imply that the mean mass-to-flux ratio in molecular cores is ∼ 2-3 times critical, which means that magnetic fields are generally not strong enough to prevent gravitational collapse. However, this information about mean field strengths is not definitive in excluding one or the other of the two models of star formation. Present data do suggest that magnetic fields play a very significant role in the evolution of molecular clouds and in the star formation process. Finally, very preliminary results are discussed from two in-progress studies; these studies have the potential to be significantly more definitive in testing the predictions of star formation theory, and perhaps in discriminating between the two theories.
