CN Zeeman observations of molecular cloud cores

We present results from the first attempt to measure strengths of magnetic fields in dense molecular cloud cores by observations of the Zeeman effect in the 3 mm lines of CN. The observations were made with the 30 m IRAM radio telescope with a new polarimeter constructed for this experiment. The two molecular cores which were observed are located about 3' north of Orion-KL (OMC-N4) and about 1' east of IRS 4 in S106 (S106-CN). From CN data for OMC-N4 and S106-CN, respectively, we estimate cloud radii of 0.03 and 0.05 pc, masses of 10 and 22 M., and H-2 densities of 1.6 x 10(6) cm(-3). Our CN Zeeman results for the line-of-sight magnetic fields are B-los(OMC-N4) = +79 +/- 99 mu G and B-los(S106-CN) = -57 +/- 199 mu G. Hence, we did not detect magnetic fields. Our upper limits for B-los are significantly less than field:strengths expected for assumption of internal motions at the Alfven speed, of a critical mass to magnetic flux ratio, or of virial equilibrium, but the very small sample of clouds and the uncertainties in the \B\(Alfven), \B\(critical), and \B\(virial) estimates preclude definite conclusions.