BISTROs and Varying Magnetic Fields with Density in Serpens Main

The B-fields in Star-forming Region Observations (BISTRO) is a large program of the James Clerk Maxwell Telescope (JCMT) to study the roles of magnetic fields in molecular clouds on intermediate scales (a few thousands au or larger scales), in which a large number of researchers over the world are involved. This project was initiated in 2016 with polarimetric observations of nearby star-forming regions and has been extended toward massive and farther regions (BISTRO-2) and various evolutionary stages and environmental conditions (BISTRO-3). The current status of the BISTRO projects is reported. In addition, we discuss magnetic fields in the Serpens Main molecular cloud, which is one of the BISTRO star-forming regions. Utilizing the Histogram of Relative Orientations method, which compares polarization directions with density gradients, we show that magnetic fields are parallel to filaments in less dense filamentary structures but perpendicular to dense ones. Furthermore, the magnetic field directions with respect to density gradients vary again with density in denser core regions, which is understood by core formation and pinched fields. Note: (PI) D. Ward-Thompson, (co-PIs) P. Bastien, T. Hasegawa, W. Kwon, S. Lai, and K. Qiu