Infrared and optical polarimetry around the low-mass star-forming region NGC 1333 IRAS 4A

摘要

We performed J- and R-band linear polarimetry with the 4.2 m William HerschelTelescope at the Observatorio del Roque de los Muchachos and with the 1.6 mtelescope at the Observat\'orio do Pico dos Dias, respectively, to derive themagnetic field geometry of the diffuse molecular cloud surrounding the embeddedprotostellar system NGC 1333 IRAS 4A. We obtained interstellar polarizationdata for about two dozen stars. The distribution of polarization positionangles has low dispersion and suggests the existence of an ordered magneticfield component at physical scales larger than the protostar. Some of theobserved stars present intrinsic polarization and evidence of being youngstellar objects. The estimated mean orientation of the interstellar magneticfield as derived from these data is almost perpendicular to the main directionof the magnetic field associated with the dense molecular envelope around IRAS4A. Since the distribution of the CO emission in NGC 1333 indicates that thediffuse molecular gas has a multi-layered structure, we suggest that theobserved polarization position angles are caused by the superposed projectionalong the line of sight of different magnetic field components.