The study of SiO masers in evolved stras using mm-VLBI

1.利用韩国TRAO 14-m望远镜和日本NRO 45-m望远镜对演化星星VY CMa中SiO v=1 J=2-1脉泽辐射进行了VLBI观测。结果表明，脉泽斑分布在2 - 4个恒星半径范围内，没有系统的速度结构。我们观测到13颗演化恒星的SiOv =1 J=2-1脉泽，但除VYCMa外，其它恒星都没有得到条纹。由于VY CMa是观测源中距离最远的源，建议将未观测到的源的脉泽分辨出来。利用VLBI射电天体测量探测仪（VERA），对39颗在单碟观测中表现出强脉泽辐射的演化恒星进行了SiOv = 1，2 J=1 -0的条纹探测巡天观测。3.在上述已探测到的演化恒星中，我们选取了NML Tau、WX Psc和R Aqr，利用VERA对SiO v= 1，2 J=1-0脉泽进行了VLBI监测观测。NML Tau的脉泽分布呈椭圆环结构。9个历元的观测结果表明，在0.9光度位相附近，拟合椭圆环的大小减小，下一个光度位相椭圆环的长轴方向发生变化。

1.We have made the VLBI observations of SiO v=1 J=2-1 maser emission in the evolved star VY CMa between TRAO 14-m telescope in Korea and NRO 45-m telescope in Japan. The result shows that maser spots distribute within the region of 2 - 4 stellar radii and no systematic velocity structures are shown. We have observed SiO v=1 J=2-1 masers for 13 evolved stars, but we could not get fringes from them except VY CMa. The masers of the non-detected sources are suggested to be resolved out because VY CMa is the farthest one among the observed sources. The size of J=2-1 maser region may be larger than that of J=1-0 maser region considering the following J =1-0 fringe survey results.2.Using VERA (VLBI Exploration of Radio Astrometry), the fringe detection survey observations of SiO v=1,2 J=1-0 were made for 39 evolved stars which show strong maser emission in our single-dish monitoring observations. We could find fringes from 13 sources in which mira, OH/IR star, supergiant and semiregular variable were contained.3.We have selected NML Tau, WX Psc and R Aqr among above detected evolved stars, and have made VLBI monitoring observations of SiO v=1,2 J=1-0 masers using VERA. The maser distribution in NML Tau shows an elliptical ring structure. Our 9 epoch observations show that the size of fitted elliptical ring decreased near the luminosity phase of 0.9 and the direction of major axis of elliptical ring changed at the next luminosity period.