We observed v = 1 ,J = 1 - 0 43-GHz SiO maser emission toward the Mira variable IK Tauri ( IK Tau ) using the Very Long Baseline Array ( VLBA ) .
The images resulting from these observations show that SiO masers form a highly elliptical ring of emission approximately 58 \times 32 mas with an axial ratio of 1.8:1 .
The major axis of this elliptical distribution is oriented at position angle of \sim 59 ^ { \circ } .
The line-of-sight velocity structure of the SiO masers has an apparent axis of symmetry consistent with the elongation axis of the maser distribution .
Relative to the assumed stellar velocity of 35 km s ^ { -1 } , the blue- and red-shifted masers were found to lie to the northwest and southeast of this symmetry axis respectively .
This velocity structure suggests a NW–SE rotation of the SiO maser shell with an equatorial velocity , which we determine to be \sim 3.6 km s ^ { -1 } .
Such a NW–SE rotation is in agreement with a circumstellar envelope geometry invoked to explain previous H _ { 2 } O and OH maser observations .
In this geometry , H _ { 2 } O and OH masers are preferentially created in a region of enhanced density along the NE–SW equator orthogonal to the rotation/polar axis suggested by the SiO maser velocities .