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We report on results of five-epoch VLBI observations of H2O maser emission in the M-type star IRC � 10414, carried out with the VLBI Exploration of Radio Astrometry (VERA). The maser distribution extends over an area of 70 mas � 260 mas and exhibits a bipolar structure. The relative proper motions of 17 maser features were measured during the monitoring observations spanning nine months. The distance to IRC � 10414 was re-estimated on the basis of the statistical treatment of parallax and the model-fitting method, yielding D = 3.1 ˙ 0.4 kpc and D = 2.0 ˙ 0.2 kpc, respectively. The estimated distance, D = 2–3 kpc, is much larger than that previously adopted. The stellar luminosity of IRC � 10414 is also re-estimated to be L� � 9 � 10 4 (D=2 kpc) 2 Lˇ, much brighter by a factor of 10–20 than previously adopted (L� � 10000 Lˇ). The maser motions exhibit not only a spherically expanding flow with a velocity of � 10 (D=2 kpc) km s � 1 , but also a faster bipolar outflow with a major axis in the north–south direction and at a small inclination angle with respect to the celestial sphere. These characteristics of the star and the

We report on results of multi-epoch VLBI observations of H2O masers associated with a low-mass young stellar object, IRAS 16293 2422 in Oph East, and a fringe-phase and position reference source, ICRF J162546.8 252738, using the VLBI Exploration of Radio Astrometry (VERA) for high-precision astrometry. We obtained an annual parallax of a maser feature to be = 5.6 0:5 mas, corresponding to a distance of D= 178 +18 37 pc. We also found 10 relative proper motions of maser features with respect to the maser feature mentioned above. The motion of the accompanying young stellar object (YSO) has already been found in thermal continuum emission previously observed with the Very Large Array. The intrinsic motions of masers have been estimated from the relative proper motions after the YSO’s motion is subtracted from, and a systemic secular motion of the position reference feature is added to the proper motions originally measured. The intrinsic maser kinematical structure may trace a bipolar outflow.

We report on multi-epoch observations of H2O 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. 7 ×1. 0, in addition to a ‘shell-like’ structure with a scale of 0. 3 ×0. �� 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 ∼ 8kms −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 ±0.5kpc. This distance is consistent with a near kinematic distance, and rules out a far kinematic distance (∼ 9kpc). 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 ∼ 6.3kpc.

We report on a strong outburst of the W49N H2O maser observed with VERA. Single-dish monitoring with VERA 20 m telescopes detected a strong outburst of the maser feature at V_LSR = -30.7 km/s in 2003 October. The outburst had a duration of ~100 days and a peak intensity of 7.9 x 10^4 Jy, being one of the strongest outbursts in W49N observed so far. VLBI observations with the VERA array were also carried out near to the maximum phase of the outburst, and the outburst spot was identified in the VLBI map. While the map was in good agreement with previous studies, showing three major concentrations of maser spots, we found a newly formed arc-like structure in the central maser concentration, which may be a shock front powered by a forming star or a star cluster. The outburst spot was found to be located on the arc-like structure, indicating a possible connection of the present outburst to a shock phenomenon., Comment: 4 pages, 2 figures included, to appear in PASJ letter (Vol.56, #3, 2004 June)

We present the results of first dual-beam observations with VERA (VLBI Exploration of Radio Astrometry). The first dual-beam observations of a pair of H2O maser sources W49N and OH43.8-0.1 have been carried out on 2002 May 29 and July 23, and fringes of H2O maser lines at 22 GHz have been successfully detected. While the residual fringe phases of both sources show rapid variations over 360 degree due to the atmospheric fluctuation, the differential phase between the two sources remains constant for 1 hour with r.m.s. of 8 degree, demonstrating that the atmospheric phase fluctuation is removed effectively by the dual-beam phase referencing. The analysis based on Allan standard deviation reveals that the differential phase is mostly dominated by white phase noise, and the coherence function calculated from the differential phase shows that after phase referencing the fringe visibility can be integrated for arbitrarily long time. These results demonstrate VERA's high capability of phase referencing, indicating that VERA is a promising tool for phase referencing VLBI astrometry at 10 microarcsec level accuracy., Comment: 9 pages, 3 figures included, to appear in PASJ letter (Vol.55, #4, 2003 August)

In order to search for new VLBI sources in the Galactic plane that can be used as phase reference sources in differential VLBI, we have conducted 22 GHz observations of radio sources in the Galactic plane using the Japanese VLBI Network (J-Net). We have observed 267 VLBI source candidates selected from existing radio surveys and have detected 93 sources at the signal-to-noise ratio larger than 5. While 42 of the 93 detected sources had already been detected with VLBI at relatively lower frequency (typically 2 to 8 GHz), the remaining 51 are found to be new VLBI sources detected for the first time. These VLBI sources are located within $|b|\le 5^\circ$, and have a large number of Galactic maser sources around them. Thus, they are potential candidates for phase reference sources for VLBI Exploration of Radio Astrometry (VERA), which is the first VLBI array dedicated to the phase referencing VLBI astrometry aiming at measuring the parallax and proper motion of maser sources in the whole Galaxy., Comment: to be published in PASJ (2000, Vol.52, No.5), 13 pages and 2 figures