OH masers associated with bipolar outflow in ON1

Abstract

Multi-Element Radio-Linked Interferometer Network polarization measurements of the OH 18-cm masers in ON1 are presented. OH maser emission is detected in all four ground state lines. The bulk of the masers lie in an elongated distribution covering 2 arcsec at position angle 130 ◦ , near the southern edge of the ultracompact H II region. The maser distribution is orthogonal to the bipolar outflow seen in HCO + at position angle (PA) 44 ◦ . An isolated group of 1720-MHz masers is also seen 6 arcsec to the east. The magnetic field deduced from Zeeman splitting of the OH maser lines shows a large-scale order, with field values ranging from −0.4 to −4.6 mG.