LBA observations of the maser cluster OH 330.953−0.182

• Published in: Monthly notices of the Royal Astronomical Society 2010-03, Vol.402 (4), p.2649-2656
• Main Authors: Caswell, J. L., Kramer, B. Hutawarakorn, Sukom, A., Reynolds, J. E.
• Format: Article
• Language: English
• Subjects: Astronomy; Astrophysics; Earth, ocean, space; Exact sciences and technology; H ii regions; ISM: molecules; Kinematics; Magnetic fields; masers; Morphology; radio lines: ISM; Star & galaxy formation; stars: formation
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2009.16076.x

The maser spot distribution of OH 330.953−0.182 provides a valuable probe of its massive star-forming host. We present observations with the Long Baseline Array of the Australia Telescope National Facility, of both the 1665- and 1667-MHz hydroxyl ground-state transitions, yielding a series of maps in both right- and left-hand circular polarization at velocity spacing 0.09 km s−1 with 0.1 arcsec spatial resolution. A total of 53 maser spots are spread over a remarkably large region exceeding 6 arcsec diameter. At the minimum distance estimate of 5.6 kpc, 6 arcsec corresponds to 163 mpc, much larger than the extents of previously mapped individual sites, which rarely exceed 40 mpc. Seven locations show Zeeman pairs, one of them at both 1665 and 1667 MHz corroborating the same magnetic field estimate. All measured magnetic fields are towards us (negative), and range from −3.7 to −5.8 mG. Comparisons of the morphology and kinematics of the 1665- and 1667-MHz maser spots have been made with those of the OH 1720-MHz transition, the excited state of OH at 6035 MHz, methanol at 6668 MHz, water at 22 GHz and with extensive H ii emission, all of which contribute to a better understanding of the region. We interpret the overall complexity of the region as evidence for several distinct sites of excitation, similar to the remarkable W51 complex, and in contrast to the simple morphologies of previously studied single maser sites such as OH 300.969+1.147 and W3(OH).