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Structure and Magnetic Field of the Bright-rimmed Cloud IC 1396E/SFO 38

Koji Sugitani, Jan G. A. Wouterloot, Harriet Parsons, Sarah Graves, Takayoshi Kusune, Archana Soam

TL;DR

The paper investigates how ultraviolet irradiation shapes the density structure and magnetic field of the bright-rimmed cloud IC 1396E/SFO 38 using 850 μm polarimetry with JCMT/POL-2, complemented by archival CO, Planck, and infrared data. By mapping both the dust continuum and magnetic field orientation, the authors test radiation-driven-implosion scenarios for filamentary clouds and find that the apparent two-part structure can arise from oblique illumination of a single filament, with the magnetic field reconfiguring from the ambient direction and pinching toward the cloud head. They estimate magnetic strength and stability across cloud regions, finding the head to be likely supercritical and undergoing gravitational contraction, while the field morphology supports UV-induced reconfiguration. These results illuminate the role of magnetic fields in BRC evolution and provide observational constraints on how UV feedback and gravity shape high-density clumps where intermediate-mass star formation occurs.

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 excited 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 expected to be also 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 the 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. The 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.

Structure and Magnetic Field of the Bright-rimmed Cloud IC 1396E/SFO 38

TL;DR

The paper investigates how ultraviolet irradiation shapes the density structure and magnetic field of the bright-rimmed cloud IC 1396E/SFO 38 using 850 μm polarimetry with JCMT/POL-2, complemented by archival CO, Planck, and infrared data. By mapping both the dust continuum and magnetic field orientation, the authors test radiation-driven-implosion scenarios for filamentary clouds and find that the apparent two-part structure can arise from oblique illumination of a single filament, with the magnetic field reconfiguring from the ambient direction and pinching toward the cloud head. They estimate magnetic strength and stability across cloud regions, finding the head to be likely supercritical and undergoing gravitational contraction, while the field morphology supports UV-induced reconfiguration. These results illuminate the role of magnetic fields in BRC evolution and provide observational constraints on how UV feedback and gravity shape high-density clumps where intermediate-mass star formation occurs.

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 excited 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 expected to be also 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 the 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. The 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.

Paper Structure

This paper contains 8 sections, 2 equations, 1 figure.

Table of Contents

  1. Introduction
  2. IC 1396E/SFO 38
  3. Observations and Data Reduction
  4. POL-2/SCUBA-2
  5. Archival Data
  6. Near-Infrared Data
  7. Results
  8. Cloud Structure

Figures (1)

  • Figure 1: False color image of IC 1396 (red: POSS2 red, green and blue: POSS2 blue). North is at the top and east to the left. The UV incident direction from the main exciting star (HD 206267) of IC 1396 to IC 1396E/SFO 38 is indicated by an arrow.