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Publications of the Astronomical Society of Japan | 2008

Astrometry of H2O Masers in Nearby Star-Forming Regions with VERA II SVS 13 in NGC 1333

Tomoya Hirota; Takeshi Bushimata; Yoon Kyung Choi; Mareki Honma; Hiroshi Imai; Kenzaburo Iwadate; Takaaki Jike; Osamu Kameya; Ryuichi Kamohara; Yukitoshi Kan-ya; Noriyuki Kawaguchi; Masachika Kijima; Hideyuki Kobayashi; Seisuke Kuji; Tomoharu Kurayama; Seiji Manabe; Takeshi Miyaji; Takumi Nagayama; Akiharu Nakagawa; Chung Sik Oh; Toshihiro Omodaka; Tomoaki Oyama; Satoshi Sakai; Tetsuo Sasao; Katsuhisa Sato; Katsunori M. Shibata; Yoshiaki Tamura; Kazuyoshi Yamashita

We report on the results of multi-epoch VLBI observations with VERA (VLBI Exploration of Radio Astrometry) of the 22 GHz H2O masers associated with the young stellar object SVS 13 in the NGC 1333 region. We have carried out phase-referencing VLBI astrometry and measured an annual parallax of the maser features in SVS 13 of 4.25+/-0.32 mas, corresponding to the distance of 235+/-18 pc from the Sun. Our result is consistent with a photometric distance of 220 pc previously reported. Even though the maser features were detectable only for 6 months, the present results provide the distance to NGC 1333 with much higher accuracy than photometric methods. The absolute positions and proper motions have been derived, revealing that the H2O masers with the LSR (local standard of rest) velocities of 7-8 km s-1 are most likely associated with VLA4A, which is a radio counterpart of SVS 13. The origin of the observed proper motions of the maser features are currently difficult to attribute to either the jet or the rotating circumstellar disk associated with VLA4A, which should be investigated through future high-resolution astrometric observations of VLA4A and other radio sources in NGC 1333.


Publications of the Astronomical Society of Japan | 2007

Distance to Orion KL Measured with VERA

Tomoya Hirota; Takeshi Bushimata; Yoon Kyung Choi; Mareki Honma; Hiroshi Imai; Kenzaburo Iwadate; Takaaki Jike; Seiji Kameno; Osamu Kameya; Ryuichi Kamohara; Yukitoshi Kan-ya; Noriyuki Kawaguchi; Masachika Kijima; Mi Kyoung Kim; Hideyuki Kobayashi; Seisuke Kuji; Tomoharu Kurayama; Seiji Manabe; Kenta Maruyama; Makoto Matsui; Naoko Matsumoto; Takeshi Miyaji; Takumi Nagayama; Akiharu Nakagawa; Kayoko Nakamura; Chung Sik Oh; Toshihiro Omodaka; Tomoaki Oyama; Satoshi Sakai; Tetsuo Sasao

We present the initial results of multiepoch VLBI observations of 22 GHz H2O masers in the Orion KL region with VERA (VLBI Exploration of Radio Astrometry). With the VERA dual-beam receiving system, we carried out phase-referencing VLBI astrometry, and successfully detected the annual parallax of Orion KL to be 2.29 ˙ 0.10 mas, corresponding to a distance of 437 ˙ 19 pc from the Sun. The distance to Orion KL was determined for the first time with the trigonometric parallax method in these observations. Although this value is consistent with that previously reported, 480 ˙ 80 pc, which was estimated from a statistical parallax method using the proper motions and radial velocities of the H2O maser features, our new results provide a much more accurate value with an uncertainty of only 4%. In addition to the annual parallax, we detected an absolute proper motion of the maser feature, suggesting an outflow motion powered by the radio source I along with the systematic motion of source I itself.


Publications of the Astronomical Society of Japan | 2007

Astrometry of Galactic Star-Forming Region Sharpless 269 with VERA: Parallax Measurements and Constraint on Outer Rotation Curve

Mareki Honma; Takeshi Bushimata; Yoon Kyung Choi; Tomoya Hirota; Hiroshi Imai; Kenzaburo Iwadate; Takaaki Jike; Osamu Kameya; Ryuichi Kamohara; Yukitoshi Kan-ya; Noriyuki Kawaguchi; Masachika Kijima; Hideyuki Kobayashi; Seisuke Kuji; Tomoharu Kurayama; Seiji Manabe; Takeshi Miyaji; Takumi Nagayama; Akiharu Nakagawa; Chung Sik Oh; Toshihiro Omodaka; Tomoaki Oyama; Satoshi Sakai; Katsuhisa Sato; Tetsuo Sasao; Katsunori M. Shibata; Motonobu Shintani; Hiroshi Suda; Yoshiaki Tamura; Miyuki Tsushima

We have performed high-precision astrometry of H2O maser sources in the Galactic star-forming region Sharpless 269 (S269) with VERA. We successfully detected a trigonometric parallax of 189 ˙ 8� as, corresponding to a source distance of 5:28 +0:24 � 0:22 kpc. This is the smallest parallax ever measured, and the first one detected beyond 5 kpc. The source distance as well as the proper motions were used to constrain the outer rotation curve of the Galaxy, demonstrating that the difference of rotation velocities at the Sun and at S269 (which is 13.1 kpc away from the Galaxy’s center) is less than 3%. This gives the strongest constraint on the flatness of the outer rotation curve, and provides a direct confirmation of the existence of a large amount of dark matter in the Galaxy’s outer disk.


Publications of the Astronomical Society of Japan | 2012

Fundamental Parameters of the Milky Way Galaxy Based on VLBI Astrometry

Mareki Honma; Takumi Nagayama; Kazuma Ando; Takeshi Bushimata; Yoon Kyung Choi; Toshihiro Handa; Tomoya Hirota; Hiroshi Imai; Takaaki Jike; Mi Kyoung Kim; Osamu Kameya; Noriyuki Kawaguchi; Hideyuki Kobayashi; Tomoharu Kurayama; Seisuke Kuji; Naoko Matsumoto; Seiji Manabe; Takeshi Miyaji; Kazuhito Motogi; Akiharu Nakagawa; Hiroyuki Nakanishi; Kotaro Niinuma; Chung Sik Oh; Toshihiro Omodaka; Tomoaki Oyama; Nobuyuki Sakai; Katsuhisa Sato; Mayumi Sato; Katsunori M. Shibata; Satoshi Shiozaki

We present analyses to determine the fundamental parameters of the Galaxy based on VLBI astrometry of 52 Galactic maser sources obtained with VERA, VLBA, and EVN. We model the Galaxy’s structure with a set of parameters, including the Galaxy center distance R0, the angular rotation velocity at the LSR Ω0, the mean peculiar motion of the sources with respect to Galactic rotation (Usrc, Vsrc, Wsrc), the rotation-curve shape index, and the V component of the Solar peculiar motions, Vˇ. Based on a Markov chain Monte-Carlo method, we find that the Galaxy center distance is constrained at a 5% level to be R0 = 8.05 ˙ 0.45 kpc, where the error bar includes both statistical and systematic errors. We also find that the two components of the source peculiar motion Usrc and Wsrc are fairly small compared to the Galactic rotation velocity, being Usrc = 1.0 ˙ 1.5 km s � 1 and Wsrc = � 1.4 ˙ 1.2 km s � 1 . Also, the rotation curve shape is found to be basically flat between Galacto-centric radii of 4 and 13 kpc. On the other hand,


The Astronomical Journal | 2014

EARLY SCIENCE WITH THE KOREAN VLBI NETWORK: EVALUATION OF SYSTEM PERFORMANCE

Sang-Sung Lee; Leonid Petrov; Do-Young Byun; Jongsoo Kim; Taehyun Jung; Min-Gyu Song; Chung Sik Oh; Duk-Gyoo Roh; Do-Heung Je; Seog-Oh Wi; Bong Won Sohn; Se-Jin Oh; Kee-Tae Kim; Jae-Hwan Yeom; Moon-Hee Chung; Jiman Kang; Seog-Tae Han; Jung-Won Lee; Bong Gyu Kim; Hyunsoo Chung; Hyun-Goo Kim; Hyo Ryoung Kim; Yong-Woo Kang; Se-Hyung Cho

We report the very long baseline interferometry (VLBI) observing performance of the Korean VLBI Network (KVN). The KVN is the first millimeter-dedicated VLBI network in East Asia. The KVN consists of three 21 m radio telescopes with baseline lengths in a range of 305-476 km. The quasi-optical system equipped on the antennas allows simultaneous observations at 22, 43, 86, and 129 GHz. The first fringes of the KVN were obtained at 22 GHz on 2010 June 8. Test observations at 22 and 43 GHz on 2010 September 30 and 2011 April 4 confirmed that the full cycle of VLBI observations works according to specification: scheduling, antenna control system, data recording, correlation, post-correlation data processing, astrometry, geodesy, and imaging analysis. We found that decorrelation due to instability in the hardware at times up to 600 s is negligible. The atmosphere fluctuations at KVN baseline are partly coherent, which allows us to extend integration time under good winter weather conditions up to 600 s without significant loss of coherence. The post-fit residuals at KVN baselines do not exhibit systematic patterns, and the weighted rms of the residuals is 14.8 ps. The KVN is ready to image compact radio sources both in snapshot and full-track modes with residual noise in calibrated phases of less than 2 deg at 22 and 43 GHz and with dynamic ranges of ~300 for snapshot mode and ~1000 for full-track mode. With simultaneous multi-frequency observations, the KVN can be used to make parsec-scale spectral index maps of compact radio sources.


Publications of the Astronomical Society of Japan | 2008

Distance to VY Canis Majoris with VERA

Yoon Kyung Choi; Tomoya Hirota; Mareki Honma; Hideyuki Kobayashi; Takeshi Bushimata; Hiroshi Imai; Kenzaburo Iwadate; Takaaki Jike; Seiji Kameno; Osamu Kameya; Ryuichi Kamohara; Yukitoshi Kan-ya; Noriyuki Kawaguchi; Masachika Kijima; Mi Kyoung Kim; Seisuke Kuji; Tomoharu Kurayama; Seiji Manabe; Kenta Maruyama; Makoto Matsui; Naoko Matsumoto; Takeshi Miyaji; Takumi Nagayama; Akiharu Nakagawa; Kayoko Nakamura; Chung Sik Oh; Toshihiro Omodaka; Tomoaki Oyama; Satoshi Sakai; Tetsuo Sasao

We report astrometric observations of H2O masers around the red supergiant VY Canis Majoris (VY CMa) carried out with VLBI Exploration of Radio Astrometry (VERA). Based on astrometric monitoring for 13 months, we successfully measured a trigonometric parallax of 0.88 ± 0.08 mas, corresponding to a distance of 1.14 +0.11 −0.09 kpc. This is the most accurate distance to VY CMa and the first one based on an annual parallax measurement. The luminosity of VY CMa has been overestimated due to a previously accepted distance. With our result, we re-estimate the luminosity of VY CMa to be (3 ± 0.5) × 10 5 L⊙ using the bolometric flux integrated over optical and IR wavelengths. This improved luminosity value makes location of VY CMa on the Hertzsprung-Russel (HR) diagram much closer to the theoretically allowable zone (i.e. the left side of the Hayashi track) than previous ones, though uncertainty in the effective temperature of the stellar surface still does not permit us to make a final conclusion.


Astrophysical Journal Supplement Series | 2010

Simultaneous Observations of SiO and H2O Masers Toward Known Stellar SiO and H2O Maser Sources. I.

Jaeheon Kim; Se-Hyung Cho; Chung Sik Oh; Do-Young Byun

We present the results of simultaneous observations of both SiO and H2O masers toward 166 known SiO and H2O maser sources using the Korean VLBI Network Yonsei 21 m radio telescope during 2009 June. Both SiO and H2O maser emission were detected from 112 sources giving a detection rate of 67% at one epoch observation. SiO-only maser emission was detected from 42 sources, while H2O-only maser emission was detected from four sources. Most of the SiO masers appear around the stellar velocity, while H2O masers show different characteristics compared with SiO masers. There are more than 20 sources that show a one-way peak or double peaks with respect to the stellar velocity and SiO maser peak velocity. The H2O maser peak and integrated intensity ratios with respect to those of SiO (v = 1) show increasingly larger values from Mira variables, to OH/IR stars, to semi-regular variables. In addition, the IRAS two-color diagram of SiO and H2O maser observational results is discussed.


Publications of the Astronomical Society of Japan | 2008

Astrometry of H2O Masers in Nearby Star-Forming Regions with VERA III. IRAS22198+6336 in Lynds1204G

Tomoya Hirota; Kazuma Ando; Takeshi Bushimata; Yoon Kyung Choi; Mareki Honma; Hiroshi Imai; Kenzaburo Iwadate; Takaaki Jike; Seiji Kameno; Osamu Kameya; Ryuichi Kamohara; Yukitoshi Kan-ya; Noriyuki Kawaguchi; Masachika Kijima; Mi Kyoung Kim; Hideyuki Kobayashi; Seisuke Kuji; Tomoharu Kurayama; Seiji Manabe; Makoto Matsui; Naoko Matsumoto; Takeshi Miyaji; Atsushi Miyazaki; Takumi Nagayama; Akiharu Nakagawa; D. Namikawa; Daisuke Nyu; Chung Sik Oh; Toshihiro Omodaka; Tomoaki Oyama

We present results of multi-epoch VLBI observations with VERA (VLBI Exploration of Radio Astrometry) of the 22 GHz H2O masers associated with a young stellar object (YSO) IRAS 22198+6336 in a dark cloud, L 1204 G. Based on phase-referencing VLBI astrometry, we derived an annual parallax of IRAS 22198+6336 to be 1.309˙ 0.047 mas, corresponding to the distance of 764˙ 27 pc from the Sun. Although the most principal error source of our astrometry is attributed to the internal structure of the maser spots, we successfully reduced the errors in the derived annual parallax by employing position measurements for all of the 26 detected maser spots. Based on this result, we reanalyzed the spectral energy distribution of IRAS 22198+6336 and found that the bolometric lumi— —


Publications of the Astronomical Society of Japan | 2008

Distance to NGC 281 in a Galactic Fragmenting Superbubble: Parallax Measurements with VERA

Mayumi Sato; Tomoya Hirota; Mareki Honma; Hideyuki Kobayashi; Tetsuo Sasao; Takeshi Bushimata; Yoon Kyung Choi; Hiroshi Imai; Kenzaburo Iwadate; Takaaki Jike; Seiji Kameno; Osamu Kameya; Ryuichi Kamohara; Yukitoshi Kan-ya; Noriyuki Kawaguchi; Mi Kyoung Kim; Seisuke Kuji; Tomoharu Kurayama; Seiji Manabe; Makoto Matsui; Naoko Matsumoto; Takeshi Miyaji; Takumi Nagayama; Akiharu Nakagawa; Kayoko Nakamura; Chung Sik Oh; Toshihiro Omodaka; Tomoaki Oyama; Satoshi Sakai; Katsuhisa Sato

We have used the Japanese VLBI array VERA to perform high-precision astrometry of an H2O maser source in the Galactic star-forming region NGC 281 West, which has been considered to be part of a 300-pc superbubble. We successfully detected a trigonometric parallax of 0.355 ˙ 0.030 mas, corresponding to a source distance of 2.82 ˙ 0.24 kpc. Our direct distance determination of NGC 281 has resolved a large distance discrepancy between previous photometric and kinematic studies; likely NGC 281 is in the far side of the Perseus spiral arm. The source distance as well as the absolute proper motions were used to demonstrate the 3D structure and expansion of the NGC 281 superbubble, � 650 pc in size parallel to the Galactic disk and with a shape slightly elongated along the disk or spherical, but not vertically elongated, indicating that the superbubble expansion may be confined to the disk. We estimate the expansion velocity of the superbubble as being � 20 km s � 1 , both perpendicular to and parallel to the Galactic disk with a consistent timescale of � 20 Myr.


Publications of the Astronomical Society of Japan | 2008

VLBI Astrometry of AGB Variables with VERA — A Semiregular Variable S Crateris—

Akiharu Nakagawa; Miyuki Tsushima; Kazuma Ando; Takeshi Bushimata; Yoon Kyung Choi; Tomoya Hirota; Mareki Honma; Hiroshi Imai; Kenzaburo Iwadate; Takaaki Jike; Seiji Kameno; Osamu Kameya; Ryuichi Kamohara; Yukitoshi Kan-ya; Noriyuki Kawaguchi; Masachika Kijima; Mi Kyoung Kim; Hideyuki Kobayashi; Seisuke Kuji; Tomoharu Kurayama; Toshihisa Maeda; Seiji Manabe; Kenta Maruyama; Makoto Matsui; Naoko Matsumoto; Takeshi Miyaji; Takumi Nagayama; Kayoko Nakamura; Daisuke Nyu; Chung Sik Oh

We present a distance measurement for the semiregular variable S Crateris (S Crt) based on its annual parallax. With the unique dual beam system of the VLBI Exploration for Radio Astrometry (VERA) telescopes, we measured the absolute proper motion of a water maser spot associated with S Crt, referred to the quasar J1147� 0724 located . .. . .. . .. . ..

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Mareki Honma

Graduate University for Advanced Studies

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Noriyuki Kawaguchi

Graduate University for Advanced Studies

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Tomoharu Kurayama

Teikyo University of Science

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Seiji Manabe

Graduate University for Advanced Studies

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Takaaki Jike

Graduate University for Advanced Studies

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