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EVOLUTION OF THE WATER MASER EXPANDING SHELL IN W75N VLA 2
Kim, Jeong-Sook,Kim, Soon-Wook,Kurayama, Tomoharu,Honma, Mareki,Sasao, Tesuo,Surcis, Gabriele,Cantó,, Jorge,Torrelles, José,M.,Kim, Sang Joon IOP Publishing 2013 The Astrophysical journal Vol.767 No.1
<P>We present Very Long Baseline Interferometry (VLBI) observations of 22 GHz H2O masers in the high-mass star-forming region of W75N, carried out with VLBI Exploration of Radio Astrometry (VERA) for three epochs in 2007 with an angular resolution of similar to 1 mas. We detected H2O maser emission toward the radio jet in VLA 1 and the expanding shell-like structure in VLA 2. The spatial distribution of the H2O masers detected with VERA and measured proper motions around VLA 1 and VLA 2 are similar to those found with previous VLBI observations in epochs 1999 and 2005, with the masers in VLA 1 mainly distributed along a linear structure parallel to the radio jet and, on the other hand, forming a shell-like structure around VLA 2. We have made elliptical fits to the VLA 2 H2O maser shell-like structure observed in the different epochs (1999, 2005, and 2007), and found that the shell is still expanding eight years after its discovery. From the difference in the size of the semi-major axes of the fitted ellipses in epochs 1999 (similar or equal to 71 +/- 1 mas), 2005 (similar or equal to 97 +/- 3 mas), and 2007 (similar or equal to 111 +/- 1 mas), we estimate an average expanding velocity of similar to 5 mas yr(-1), similar to the proper motions measured in the individual H2O maser features. A kinematic age of similar to 20 yr is derived for this structure. In addition, our VERA observations indicate an increase in the ellipticity of the expanding shell around VLA 2 from epochs 1999 to 2007. In fact, the elliptical fit of the VERA data shows a ratio of the minor and major axes of similar to 0.6, in contrast with an almost circular shape for the shell detected in 1999 and 2005 (b/a similar to 0.9). This suggests that we are probably observing the formation of a jet-driven H2O maser structure in VLA2, evolving from a non-collimated pulsed-outflow event during the first stages of evolution of a massive young stellar object (YSO). This may support predictions made earlier by other authors on this issue, consistent with recent magnetohydrodynamical simulations. We discuss possible implications of our results in the study of the first stages of evolution of massive YSOs.</P>
Cho, Jae-Sang,Kan-Ya, Yukitoshi,Byun, Yong-Ik,Kurayama, Tomoharu,Choi, Yoon-Kyung,Kim, Mi-Kyoung The Korean Astronomical Society 2010 Journal of The Korean Astronomical Society Vol.43 No.2
We report relative proper motion measurements of $H_{2}O$ masers in massive star-forming region W51 Main, based on data sets of VLBI observations for $H_{2}O$ masers at 22 GHz with Japanese VERA telescopes from 2003 to 2006. Data reductions and single-beam imaging analysis are to measure internal kinematics of maser spots and eventually to estimate the three-dimensional kinematics of $H_{2}O$ masers in W51 Main. Average space motions and proper motion measurements of $H_{2}O$ masers are given both graphical and in table formats. We find in this study that W51 Main appears to be associated with hyper-compact H II region with multiple massive proto-stars whose spectral types are of late O.
대전 상관기의 전처리를 위한 광역 프린지 탐색 소프트웨어 개발 및 시험
오세진,노덕규,윤영주,염재환,오충식,쿠라야마 토모하루,정동규,정진승,Oh, Se-Jin,Roh, Duk-Gyoo,Yun, Young-Joo,Yeom, Jae-Hwan,Oh, Chung-Sik,Kurayama, Tomoharu,Chung, Dong-Kyu,Jung, Jin-Seung 한국융합신호처리학회 2014 융합신호처리학회 논문지 (JISPS) Vol.15 No.4
본 논문에서는 대전상관기의 전처리를 위한 광역 프린지 탐색 소프트웨어 개발에 대해 기술한다. VLBI 관측의 경우 전파망원경에 의해 천체를 잘 관측하였는지 확인하기 위해 관측자는 관측일정에서 잘 알려져 있는 전파세기가 강하고 밝은 천체(포인터 소스, 참조천체)를 목적천체와 함께 관측을 수행한다. 상관기는 참조천체를 대상으로 상관 프린지가 잘 검출되는지 확인하는 전처리를 수행한다. 본 논문에서는 특정 관측국을 기준으로 각 관측국 사이의 정확한 지연시각을 계산하는 GFS 소프트웨어를 개발하였는데, 이 소프트웨어는 상관 전처리를 통하여 각 관측국에 위치한 수소원자시계와 GPS 시각 사이의 시각오차 정보 및 참조천체의 지연모델(상관모델)을 이용하여 정확한 지연시각을 계산한다. 개발한 소프트웨어의 성능을 확인하기 위한 상관 전처리 시험을 KaVA 관측망으로 관측한 참조천체와 목적천체에 대해 수행하였다. 시험결과는 GFS 소프트웨어로 찾은 지연시각 오차를 보정한 결과와 그렇지 않은 것의 비교에 따라 매우 좋은 성능을 보여 효과적임을 나타내었다. This paper introduces the development of global fringe search (GFS) software for preprocessing of Daejeon Correlator. In case of the VLBI observation, a observer conducts the observation for the reference sources with strong and point-like radio stars on schedule in order to confirm the well-observedness of the radio source by the radio telescope. The correlator performs the correlation for the reference sources to detect the fringe completely. We developed the GFS software by calculating the precise delay time between each observatory based on specific observatory. Then, this software calculates the precise delay time by using the delay model (correlator model) of reference source and information of time offset between the Hydrogen Maser frequency standard and GPS (Global Positioning System) clock located in each observatory through the correlation preprocessing. In order to confirm the performance of the developed software, experiments were carried out for the reference sources and target sources observed by the KaVA (KVN and VERA Array). Experimental results show that the GFS software has effectively good performance by finding the precise delay time offset according to the comparison between the compensated delay time offset and one without compensation.