The magnetic field at milliarcsecond resolution around IRAS 20126+4104

¹ Joint Institute for VLBI in Europe, Postbus 2, 79990 AA Dwingeloo, The Netherlands
² Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
³ Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁵ Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶ National Astronomical Research Institute of Thailand, Ministry of Science and Technology, Rama VI Rd., 10400 Bangkok, Thailand

Received: 4 October 2013
Accepted: 20 January 2014

Abstract

Context. IRAS 20126+4104 is a well studied B0.5 protostar that is surrounded by a ~1000 au Keplerian disk and is where a large-scale outflow originates. Both 6.7-GHz CH₃OH masers and 22-GHz H₂O masers have been detected toward this young stellar object. The CH₃OH masers trace the Keplerian disk, while the H₂O masers are associated with the surface of the conical jet. Recently, observations of dust polarized emission (350 μm) at an angular resolution of 9 arcsec (~15 000 au) have revealed an S-shaped morphology of the magnetic field around IRAS 20126+4104.

Aims. The observations of polarized maser emissions at milliarcsecond resolution (~20 au) can make a crucial contribution to understanding the orientation of the magnetic field close to IRAS 20126+4104. This will allow us to determine whether the magnetic field morphology changes from arcsecond resolution to milliarcsecond resolution.

Methods. The European VLBI Network was used to measure the linear polarization and the Zeeman splitting of the 6.7-GHz CH₃OH masers toward IRAS 20126+4104. The NRAO Very Long Baseline Array was used to measure the linear polarization and the Zeeman splitting of the 22-GHz H₂O masers toward the same region.

Results. We detected 26 CH₃OH masers and 5 H₂O masers at high angular resolution. Linear polarization emission was observed toward three CH₃OH masers and toward one H₂O maser. Significant Zeeman splitting was measured in one CH₃OH maser (ΔV_Z = −9.2 ± 1.4 m s^-1). No significant (5σ) magnetic field strength was measured using the H₂O masers. We found that in IRAS 20126+4104 the rotational energy is less than the magnetic energy.