Multi-Epoch VERA Observations of H2O Masers in OH 43.8-0.1

M. Honma, T. Bushimata, Y.K. Choi, T. Fujii, T. Hirota, K. Horiai, H. Imai, N. Inomata, J. Ishitsuka, K. Iwadate, T. Jike, O. Kameya, R. Kamohara, Y. Kan-Ya, N. Kawaguchi, M. Kijima, H. Kobayashi, S. Kuji, T. Kurayama, S. ManabeT. Miyaji, A. Nakagawa, K. Nakashima, C.S. Oh, T. Omodaka, T. Oyama, Maria Rioja Capellan, S. Sakai, K. Sato, T. Sasao, K.M. Shibata, R. Shimizu, K. Sora, H. Suda, Y. Tamura, K. Yamashita, D Green

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    Abstract

    We report on the multi-epoch observations of H2O maser emission in star forming region OH 43.8-0.1 carried out with VLBI Exploration of Radio Astrometry (VERA). The large-scale maser distributions obtained by single-beam VLBI mapping reveal new maser spots scattered in area of 0.7 x 1.0 arcsec, in addition to a `shell-like' structure with a scale of 0.3 x 0.5 arcsec which was previously mapped by Downes et al.(1979). Proper motions are also obtained for 43 spots based on 5-epoch monitoring with a time span of 281 days. The distributions of proper motions show a systematic outflow in the north-south direction with an expansion velocity of ~8 km/s, and overall distributions of maser spots as well as proper motions are better represented by a bipolar flow plus a central maser cluster with a complex structure, rather than a shell with a uniform expansion such as those found in Cep A R5 and W75N VLA2. The distance to OH 43.8-0.1 is also estimated based on the statistical parallax, yielding D = 2.8 +/- 0.5 kpc. This distance is consistent with a near kinematic distance and rules out a far kinematics distance (~9 kpc), and the LSR velocity of OH 43.8-0.1 combined with the distance provides a constraint on the flatness of the galactic rotation curve, that there is no systematic difference in rotation speeds at the Sun and at the position of OH 43.8-0.1, which is located at the galacto-centric radius of ~6.3 kpc
    Original languageEnglish
    Pages (from-to)595-603
    JournalPublications of the Astronomical Society of Japan
    Volume57
    Issue number4
    Publication statusPublished - 2005

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