The Magnetic Fields in the Ophiuchus and Taurus Molecular Clouds

Abstract

We discuss the significance of previously published OH Zeeman effect measurements of the magnetic field in the p Oph cloud (L1688) and also a new OH Zeeman effect measurement for the dark cloud core TMC-1C, the latter obtained with the Arecibo telescope. Results for both of these clouds, like previously published OH Zeeman results for other dark clouds, show that the line-of-sight field strength |B ∥ |≤ 10 μG. The p Oph cloud is significantly higher in column density than other clouds studied, and recent H I Zeeman effect observations have revealed B ∥ ≈ +10 μG in the H I self-absorption region in front of the cloud. The low values of B ∥ derived from the OH Zeeman effect may indicate that OH poorly samples the dense gas in the ρ Oph cloud, or else that the cloud is in a state of supercritical collapse. The TMC-1C cloud core may have formed via ambipolar diffusion in a manner similar to recent modeling of dark cloud Barnard 1. © 1996. The American Astronomical Society. All rights reserved.