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

1.利用韩国的TRAO 14-m望远镜和日本的NRO 45-m望远镜对演化恒星VY CMa的SiO v=1 J=2-1脉泽发射进行了VLBI观测。结果表明，微波激射斑分布在2 ~ 4星半径范围内，没有系统的速度结构。我们已经观测到13颗演化恒星的SiO v=1 J=2-1脉泽，但除了VY CMa外，我们没有观测到它们的条纹。由于VY CMa是观测到的源中最远的源，因此建议对未探测到的源的脉泽进行分辨。考虑到以下J=1-0条纹测量结果，J=2-1脉泽区域的大小可能大于J=1-0脉泽区域。利用VERA （VLBI Exploration of Radio Astrometry）对39颗演化恒星进行了SiO v=1,2 J=1-0的条纹探测巡天观测，这些恒星在单碟观测中显示出强烈的脉泽发射。我们从13个光源中发现了包含mira、OH/IR星、超巨星和半规则变星的条纹。我们选择了NML Tau、WX Psc和R Aqr，并利用VERA对SiO v=1,2 J=1-0脉泽进行了VLBI监测观测。NML Tau的脉泽分布呈椭圆形环状结构。9历元观测结果表明，在光度相位为0.9附近，拟合椭圆环的尺寸减小，在下一个光度周期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.