The Astrometric Animation of Water Masers towards the Mira Variable BX Cam

分类： 天文学 >> 天文学 提交时间： 2023-02-19

Shuangjing Xu Hiroshi Imai Youngjoo Yun Bo Zhang Maria J. Rioja Richard Dodson Se-Hyung Cho Jaeheon Kim Lang Cui Andrey M. Sobolev James O. Chibueze Dong-Jin Kim Kei Amada Jun-ichi Nakashima Gabor Orosz Miyako Oyadomari Sejin Oh Yoshinori Yonekura Yan Sun Xiaofeng Mai

摘要： We report VLBI monitoring observations of the 22 GHz water (H$_{2}$O) masers around the Mira variable BX Cam, which were carried out as a part of the EAVN Synthesis of Stellar Maser Animations (ESTEMA) project. Data of 37 epochs in total were obtained from 2018 May to 2021 June with a time interval of 3-4 weeks, spanning approximately three stellar pulsation periods ($P= \sim$440 d). In particular, the dual-beam system equipped on the VERA stations was used to measure the kinematics and parallaxes of the H$_{2}$O maser features. The measured parallax, $\pi=1.79\pm 0.08$ mas, is consistent with $Gaia$ EDR3 and previously measured VLBI parallaxes within a 1-$\sigma$ error level. The position of the central star was estimated, based on both the $Gaia$ EDR3 data and the center position of the ring-like 43 GHz silicon-monoxide (SiO) maser distribution imaged with the KVN. The three-dimensional H$_{2}$O maser kinematics indicates that the circumstellar envelope is expanding at a velocity of $13\pm4$ km s$^{-1}$, while there are asymmetries in both the spatial and velocity distributions of the maser features. Furthermore, the H$_{2}$O maser animation achieved by our dense monitoring program manifests the propagation of shock waves in the circumstellar envelope of BX Cam.

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