Millimetre polarization of the protoplanetary nebula OH 231.8+4.2: a follow-up study with CARMA

In order to investigate the characteristics and influence of the magnetic field in evolved stars, we performed a follow-up investigation of our previous submillimetre analysis of the protoplanetary nebula (PPN) OH 231.8+4.2, this time at 1.3 mm with the CARMA (Combined Array for Research in Millimeter-wave Astronomy) facility in polarization mode for the purpose of a multiscale analysis. OH 231.8+4.2 was observed at ∼2.5 arcsec resolution, and we detected polarized emission above the 3σ threshold (with a mean polarization fraction of 3.5 per cent). The polarization map indicates an overall organized magnetic field within the nebula. The main finding in this paper is the presence of a structure mostly compatible with an ordered toroidal component that is aligned with the PPN's dark lane. We also present some alternative magnetic field configuration to explain the structure observed. These data complete our previous SMA submillimetre data for a better investigation and understanding of the magnetic field structure in OH 231.8+4.2.