SiO MASERS IN ASYMMETRIC MIRAS. III. IK TAURI

This is the third paper in a series of multi-epoch observations at 7 mm wavelength of the SiO masers in several asymptotic giant branch stars from a sample of Mira variable stars showing evidence of asymmetric structure in the infrared. These stars have been observed interferometrically in the infrared by Infrared Optical Telescope Array and with Very Long Baseline Array measurements of the SiO masers. In this paper, we present the observations of IK Tauri (IK Tau). There is a persistent elliptical distribution of the masers around the star similar to 40 x similar to 30 mas in size with a major axis at position angle similar to 30 degrees. The SiO masers in the circumstellar envelope exhibit large-scale systematic motions which reverse direction on timescales of a decade, roughly the interval between the ejections of dust shells. The orientations on the sky of the apparent rotation-like bulk motion and of the major axis of the maser ellipse differ by 37 degrees (2.5 sigma) making any relationship uncertain. The systemic velocity of IK Tau is estimated to be 33.3 +/- 1.0 km s(-1). A comparison is made with the model calculations of Gray et al. which predict some but not all observed features.