Inward motions of the compact SiO masers around VX Sagittarii
Inward motions of the compact SiO masers around VX Sagittarii
复制标题
VX 人马座周围紧凑 SiO 脉泽的向内运动
DOI：
10.1086/500168
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发表时间：
2006-04-01
影响因子：
4.9
通讯作者：
Kamohara, R
中科院分区：
文献类型：
--
作者：
Chen, X;Shen, ZQ;Kamohara, R
本文报道了1999年4 - 5月期间在M-型半正则变星星星VX Sgr的拱星包层中观测到的4 3GHz上升速度= 1，J = 1-0 SiO脉泽的三个历元的甚长基线阵列（VLBA）观测结果。这些高分辨率VLBA图像揭示了一个持久的SiO脉泽的环状分布，其投影半径约为3个恒星半径。从脉泽斑的两点相关函数分析中估计了单个脉泽特征的典型角尺寸为0.5质量。我们发现脉泽特征的表观尺寸尺度明显小于以前的观测中观察到的，通过比较它们的总功率成像的分数。脉泽辐射大小尺度的这种变化可能与观测期间引起大的SiO耀斑的恒星活动有关。我们的观测结果证实了脉泽辐射的不对称分布，但总体形态发生了显着变化，与1992年大部分脉泽位于西南部相比，大部分脉泽聚集在星星的东北部。通过识别所有三个时期出现的42个匹配的脉泽特征，我们确定了SiO脉泽壳层以-0.507 +/- 0.069 mas yr（-1）的自行向VX Sgr收缩，相当于在距离VX Sgr 1.7 kpc处的速度约为4 km s（-1）。这样的速度是在声速的数量级，可以很容易地解释为重力下降的物质从星周尘埃壳。
We report Very Long Baseline Array (VLBA) observations of 43 GHz upsilon = 1, J = 1-0 SiO masers in the circumstellar envelope of the M-type semiregular variable star VX Sgr at three epochs during 1999 April-May. These high-resolution VLBA images reveal a persistent ringlike distribution of SiO masers with a projected radius of approximate to 3 stellar radii. The typical angular size of 0.5 mas for individual maser features was estimated from two-point correlation function analysis of maser spots. We found that the apparent size scale of maser features was distinctly smaller than that observed in the previous observations by comparing their fractions of the total power imaged. This change in the size scale of maser emission may be related to stellar activity that caused a large SiO flare during our observations. Our observations confirmed the asymmetric distribution of maser emission, but the overall morphology has changed significantly, with the majority of the masers clustering to the northeast of the star compared to the majority of the masers lying in the southwest in 1992. By identifying 42 matched maser features appearing in all three epochs, we determined the contraction of an SiO maser shell toward VX Sgr at a proper motion of -0.507 +/- 0.069 mas yr(-1), corresponding to a velocity of about 4 km s(-1) at a distance of 1.7 kpc to VX Sgr. Such a velocity is on the order of the sound speed and can be easily explained by the gravitational infall of material from the circumstellar dust shell.