OH Zeeman measurement of the magnetic field in the L1544 core

We report observations with the Arecibo telescope of the Zeeman effect in the 1665 and 1667 MHz lines of OH toward eight dark cloud cores. For L1544, the inferred line-of-sight magnetic field is B-LOS = +11 +/- 2 mu G. The L1544 starless core has been observed to have infall motions; it may be very close to forming a star. B-LOS approximate to 11 mu G is consistent with the prediction of an ambipolar diffusion model computed specifically for this core before the Zeeman measurements were made; however, in order to obtain agreement with the data this model has B inclined by only 16 degrees to the plane of the sky. Virial arguments show that unless the magnetic field is mainly in the plane of the sky, it is not important for support of the L1544 core. For L1457S our result is B-LOS = -24 +/- 7 mu G, a possible but not definite detection. The other six cores were observed only with short integration times, and the Zeeman effect was not detected in these cores.