Magnetic Field Structure in Dark Clouds

Abstract

The magnetic field geometry in the central regions of two dark clouds has been mapped by measuring the polarization at 2.2 μm of background stars and of stars embedded in the clouds. The observations were done with the Kyoto polarimeter on the Agematsu 1m IR telescope in December 1984 for Heiles Cloud 2 in the Taurus dark cloud complex, and on the UKIRT 3.8m in May and July 1985 for the ρ Ophiuchus dark cloud core. The main results are: i)Most of the stars in both regions show polarization and their maxima are 2.7% in Heiles Cloud 2 and 7.6% in ρ Oph, respectively. There are similar positive relations between polarization degree and extinct ion Av's.ii)The distribution of position angles for Heiles Cloud 2 shows a single mode at about 50° and that for ρ Oph shows a bimode, at about 50° and 150°.iii)The magnetic fields, as delineated by the infrared polarization, appear perpendicular to the flattened elongations of the molecular clouds.