THE OUTER MAGNETIC FIELD OF L183

Abstract

The L183 (= L134N) dark molecular cloud has been probed using deep near-infrared imaging polarimetry of stars to beyond 14 mag in H band (1.6 μm), using the Mimir instrument on the 1.83 m Perkins Telescope. Nearly 400 arcmin2 were surveyed, including the dense core in L183, as seen in WISE Band 3 (12 μm) extinction, and the near surroundings, revealing 35 stars with either detected polarizations or significant upper limits. Stars with detected polarizations are reddened if closer than 8 arcmin (0.25 pc at the 110 pc cloud distance) and unreddened beyond. The polarimetric sample probes as close to the core as 3 arcmin (0.1 pc), where AV ~ 14 mag. Compared to the relatively unextincted surrounding stars, the reddened stars show no increase in polarization with extinction, suggesting that all of the polarization is induced in the outer layers of the cloud. This 0.25 pc radius envelope magnetic field does show a strong interaction with the L183 dark cloud. The envelope field is also virtually perpendicular, on the plane of the sky, to the field seen at 850 μm, though more closely aligned with the rotation axis of the dense gas core. The physical size scale at which the envelope and the core magnetic fields either decouple from each other or strongly modify their directions must be inside the 0.1 pc region probed here.