2025/03/07 by Shinnaga, Hiroko, Oyadomari, Miyako, Imai, Hiroshi +8
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.2503.05250
We achieved the first VLBI detections of the ground vibrational state (v=0) 28SiO (hereafter, SiO) and 29SiO masers of the J=1→ 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→ 0 transition in the v=3 state towards VY CMa for the first time with VLBI. The SiO J=1→ 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 s32, -25∘ 46′ 3.′′4) in J2000 at an absolute positional accuracy of ∼100 milliarcseconds (mas). The SiO v=0 maser spot is offset by the amount of (ΔRA, ΔDEC)=(-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 ∼ 107 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.