Velocity and magnetic fields within 1000 AU of a massive YSO^⋆

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: asanna@mpifr-bonn.mpg.de
² JIVE, Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
³ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
⁵ Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁶ Dublin Institute for Advanced Studies, School of Cosmic Physics, Astronomy & Astrophysics Section, 31 Fitzwilliam Place, Dublin 2, Ireland

Received: 22 June 2015
Accepted: 16 September 2015

Abstract

Aims. We study the velocity and magnetic field morphology in the vicinity (<1000 AU) of a massive young stellar object (YSO) at very high spatial resolution (10–100 AU).

Methods. We performed milliarcsecond polarimetric observations of the strong CH₃OH maser emission observed in the vicinity of an O-type YSO in G023.01−00.41. We combined this information with the velocity field of the CH₃OH masing gas previously measured at the same angular resolution. We analyzed the velocity and magnetic fields in the reference system defined by the direction of the molecular outflow and the equatorial plane of the hot molecular core at its base, as recently observed on subarcsecond scales.

Results. We provide a first detailed picture of the gas dynamics and magnetic field configuration within a radius of 2000 AU of a massive YSO. We have been able to reproduce the magnetic field lines for the outer regions (>600 AU) of the molecular envelope, where the magnetic field orientation shows a smooth change with the maser cloudlets position (0.2° AU^-1). Overall, the velocity field vectors accommodate the local magnetic field direction well, but still show an average misalignment of 30°. We interpret this finding as the contribution of a turbulent velocity field of about 3.5 km s^-1, which would be responsible for breaking up the alignment between the velocity and magnetic field vectors. We do resolve different gas flows that develop both along the outflow axis and across the disk plane and that have an average speed of 7 km s^-1. In the direction of the outflow axis, we establish a collimation of the gas flow at a distance of about 1000 AU from the disk plane. In the disk region, gas appears to stream outward along the disk plane for radii greater than 500–600 AU and inward for shorter radii.