Structure and magnetic field of the bright-rimmed cloud IC 1396E/SFO 38

Abstract

We carried out polarimetric observations of the bright-rimmed cloud IC 1396E/SFO 38 with SCUBA-2/POL-2 to study the effect of ultraviolet (UV) light on its structure and magnetic field. This bright-rimmed cloud appears optically to be one single cloud illuminated by the UV light from the exciting star of IC 1396. However our Stokes I image and 13CO (J = 3–2) archival data suggest that this cloud is not a simple, single structure, but appears to be composed of two parts on first glance; a head part with wings and a tail, and a north-west extension part. Since molecular clouds are generally filamentary and it seems likely that the initial structures of bright-rimmed clouds are also expected to be generally elongated, we examined the possibility that the structure was created from a single elongated cloud by the UV impact. We compared the cloud structure with a simulation study that investigated the evolution of prolate clouds exposed to UV radiation from various directions and found that this apparent two-part structure could be reproduced in a situation where a single filamentary cloud is obliquely illuminated by UV light. The magnetic field directions of the cloud are different from the ambient field direction, demonstrating the field reconfiguration. A distortion or pinch of the magnetic field is seen toward the cloud head, where an intermediate-mass star cluster is located, suggesting gravitational contraction. We roughly estimated the magnetic strength and stability in three parts of the cloud and found that the cloud head is most likely to be supercritical.