NEW ZEEMAN-EFFECT MEASUREMENTS OF THERMAL OH SOURCES S106, ORION-B, B1, AND L134 AT 1665 AND 1667 MHZ

Zeeman effect observations of four thermal OH sources, S106, B1, Orion B (NGC 2024), and L134, were carried out at 1665 and 1667 MHz with th e 140 ft radio telescope of the NRAO. The goal was to determine whethe r previous observations of the same sources by other workers using the same telescope were possibly influenced by systematic effects similar to those which have beset observations of the Zeeman effect in inters tellar HI emission profiles. The 18 cm feed used here has polarized be am structure nearly 100 times lower than was apparently the case for t he feed used by the other workers. Analysis of the new observations in dicates that the presence of nonthermal components in the putative the rmal profiles appears capable of confusing the results. Unless the exi stence of such components is ruled out, interpretation of the single-d ish radio telescope Zeeman effect may be ambiguous, even if the observ ations are performed with a feed with very low polarized beam structur e. (C) 1996 American Astronomical Society.