Oral Presentation

Magnetic field structure in star-forming regions

Eswaraiah Chakali (NCU, Taiwan), Chen Wen-Ping (NCU, Taiwan) and collaborators

We present optical and near-infrared polarimetric observations of LDN 1225 (a dark globule located towards the Cepheus OB3 cloud complex), NGC 1893 (a young open cluster with ongoing star-forming activity), and RCW 57A (a mid-infrared bipolar bubble associated with massive star formation). Our aim is to trace the magnetic field structure in various star-forming environments, and in turn
to delineate how the magnetic field governs the formation and evolution of molecular clouds, their fragmentation and further collapse to form stars. We would like to address the interplay of massive versus low-mass stars with molecular clouds, manifest as bright rimmed clouds and bubbles formed in and around OB stars. Optical polarimetric data from AIMPOL, and NIR polarimetric data from SIRPOL and MIMIR instruments lead to the following results: (i) There exist a coherent magnetic fields from large (around Cepheus OB3 cloud complex) to small scales (around LDN 1225), suggesting the influential role of magnetic field not only in the formation of a pre-existing filamentary cloud called Cepheus OB3 cloud complex but also its further fragmentation into individual clumps as seen in both C18O (Yu et al. 1996) and 13CO (Yonekura et al. 1997) observations. (ii) In NGC 1893, there is a change in the magnetic field structure within the intracluster medium,
especially around the two elephant-trunk clouds, Sim 129 and Sim 130, which is attributable to either the difference in the field strength in the pre-existing clumps, or the difference in the amount of radiation emanating from their neighboring OB stars. (iii) In RCW 57A, the NIR-polarimetry indicates that the field has shaped the cloud contraction in an hour-glass geometry. I will further discuss the implications of magnetic field geometry in view of star-formation activity inside RCW 57A.