1. First VLBI Imaging of SiO $v=0$, $J=1 \rightarrow 0$ Masers in VY Canis Majoris
- Author
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Shinnaga, Hiroko, Oyadomari, Miyako, Imai, Hiroshi, Oyama, Tomoaki, Claussen, Mark J., Shimojo, Masumi, Yamamoto, Satoshi, Richards, Anita M. S., Etoka, Sandra, Gray, Malcolm, and Suzuki, Takeru
- Subjects
Astrophysics - Solar and Stellar Astrophysics ,Astrophysics - Astrophysics of Galaxies - Abstract
We achieved the first VLBI detections of the ground vibrational state ($v=0$) $^{28}$SiO (hereafter, SiO) and $^{29}$SiO masers of the $J=1\rightarrow 0$ rotational transitions, towards the 25 \Msun ~red supergiant (RSG) star, VY Canis Majoris (VY CMa), taking advantage of the high sensitivity of the VLBI Exploration of Radio Astrometry (VERA) telescopes that coordinate with the Nobeyama 45 m telescope. In addition, we successfully detected the SiO $J=1\rightarrow 0$ transition in the $v=3$ state towards VY CMa for the first time with VLBI. The SiO $J=1\rightarrow 0$ maser spot in $v=0$ state was detected in the cross-power spectra taken with the baselines involving the Nobeyama 45-m telescope. The combination of previously reported absolute astrometry and the relative astrometry technique allowed us to derive the location of the SiO $v=0$ maser spot, {(RA, DEC) = ( 7${\rm ^h}$ 22${\rm ^m}$ 58.$^{\rm s}$32, $-$25$^{\circ}$ 46$^{\prime}$ 3.$^{\prime\prime}$4) in J2000 at an absolute positional accuracy of $\sim$100 milliarcseconds (mas). The SiO $v=0$ maser spot is offset by the amount of ($\Delta$RA, $\Delta$DEC)=($-$150, $-$300) (mas) to the southwest of the stellar position, suggesting that the $v = 0$ maser spot is associated with its outflow activity.} This observational study demonstrates that the brightest SiO $v=0$ maser spot is compact (3 mas), producing an extremely high brightness of $\sim$ 10$^7$ K. This indicates that the SiO $v=0$ maser action may originate from strong shocks in the stellar wind emanating from this extreme RSG that leads to its intense mass ejection., Comment: 10 pages, 4 figures, accepted for the publication of the Publication of Astronomical Society of Japan (PASJ)
- Published
- 2025