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

Abstract

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 $13\pm 4$ 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.

31 pages, 16 figures, accepted by ApJ

References in corpus (7)

• The Mira variable S Ori: Relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs
• Comparison of Gaia DR2 Parallaxes of Stars with VLBI Astrometry
• A New Hardware Correlator in Korea: Performance Evaluation using KVN observations
• Inner dusty envelope of the AGB stars W~Hydrae, SW\,Virginis, and R~Crateris using SPHERE/ZIMPOL
• Astrometrically Registered Simultaneous Observations of the 22 GHz H${}_2$O and the 43GHz SiO masers towards R Leonis Minoris using KVN and Source/Frequency Phase Referencing
• A comparative study of amplitude calibrations for East-Asia VLBI Network: a-priori and template spectrum methods
• Annual parallax measurement of a Mira variable star BX Cam with VERA

Cited by in corpus (4)

• Overview of the Observing System and Initial Scientific Accomplishments of the East Asian VLBI Network (EAVN)
• Long-term Simultaneous Monitoring Observations of SiO and H2O Masers toward the Mira Variable WX Serpentis
• Water vapour masers in long-period variable stars III. Mira variables U Her and RR Aql
• First Trigonometric Parallax Measurements with the KVN and VERA Array (KaVA)