| Autor: |
Honma, Mareki, Bushimata, Takeshi, Choi, Yoon Kyung, Fujii, Takahiro, Hirota, Tomoya, Horiai, Koji, Imai, Hiroshi, Inomata, Noritomo, Ishitsuka, Jose, Iwadate, Kenzaburo, Jike, Takaaki, Kameya, Osamu, Kamohara, Ryuichi, Kan-ya, Yukitoshi, Kawaguchi, Noriyuki, Kijima, Masachika, Kobayashi, Hideyuki, Kuji, Seisuke, Kurayama, Tomoharu, Manabe, Seiji, Miyaji, Takeshi, Nakagawa, Akiharu, Nakashima, Kouichirou, Oh, Chung Sik, Omodaka, Toshihiro, Oyama, Tomoaki, Rioja, Maria, Sakai, Satoshi, Sato, Katsuhisa, Sasao, Tetsuo, Shibata, Katsunori M., Shimizu, Rie, Sora, Kasumi, Suda, Hiroshi, Tamura, Yoshiaki, Yamashita, Kazuyoshi |
| Zdroj: |
Publications of the Astronomical Society of Japan; August 2005, Vol. 57 Issue: 4 p595-603, 9p |
| Abstrakt: |
We report on multi-epoch observations of $\mathrm{H}_2\mathrm{O}$maser emission in the star-forming region OH 43.8$-$0.1, carried out with VLBI Exploration of Radio Astrometry. The large-scale maser distributions obtained by single-beam VLBI mapping reveal new maser spots scattered over the area of ${0\rlap {.}{}^{\mathrm {\prime \prime }}7} \times {1\rlap {.}{}^{\mathrm {\prime \prime }}0}$, in addition to a ‘shell-like’ structure with a scale of ${0\rlap {.}{}^{\mathrm {\prime \prime }}3} \times {0\rlap {.}{}^{\mathrm {\prime \prime }}5}$, which was mapped previously. Proper motions were also obtained for 43 spots based on 5-epoch monitoring with a time span of 281 days. The distributions of the proper motions show a systematic outflow in the north-south direction with an expansion velocity of $\sim 8 \,\mathrm{km} \,\mathrm{s}^{-1}$. The overall distributions of the maser spots as well as the proper motions are better represented by a bipolar flow plus a central maser cluster with a complex structure, rather than a shell with uniform expansion, such as those found in Cep A R5 and W75N VLA2. The distance to OH 43.8$-$0.1 was also estimated based on the statistical parallax, yielding $D = 2.8 \pm 0.5 \,\mathrm{kpc}$. This distance is consistent with a near kinematic distance, and rules out a far kinematic distance ($\sim 9 \,\mathrm{kpc}$). Also, the radial velocity of the OH 43.8$-$0.1 combined with the distance provides a constraint on the flatness of the galactic rotation curve, indicating that there is no systematic difference in the rotation speeds at the Sun and at the position of OH 43.8$-$0.1, which is located at a galacto-centric radius of $\sim 6.3 \,\mathrm{kpc}$. |
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