un 2 00 3 Linear Polarization Observations of Water Masers in W 3 IRS 5

We present a magnetic field mapping of water maser clouds in the star-forming region W3 IRS 5, which has been made on the basis of the linear polarization VLBI observation. Using the Very Long Baseline Array (VLBA) at 22.2 GHz, 16 of 61 detected water masers were found to be linearly polarized with polarization degrees up to 13 %. Although 10 polarized features were widely distributed in the whole W3 IRS 5 water maser region, they had similar position angles of the magnetic field vectors (∼ 75 from the north). The magnetic field vectors are roughly perpendicular to the spatial alignments of the maser features. They are consistent with the hourglass model of the magnetic field, which was previously proposed to explain the magnetic field in the whole W3 Main region (r ∼ 0.1 pc). They are, on the other hand, not aligned to the directions of maser feature proper motions observed previously. This implies that the W3 IRS 5 magnetic field was controlled by a collapse of the W3 Main molecular cloud rather than the outflow originated from W3 IRS 5. Subject headings: ISM: jets and outflows, individual (W3 IRS 5) — masers — star:formation — Mizusawa Astrogeodynamics Observatory, National Astronomical Observatory, Mizusawa, Iwate 0230861, Japan VLBI Exploration of Radio Astrometry Project Office, National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, the Netherlands VLBI Space Observatory Programme Project Office, Natinal Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA Nobeyama Radio Observatory, National Astronomical Observatory, Minamimaki, Minamisaku, Nagano 384-1305, Japan