Changes in the velocity centroid of SiO maser emission

The v = 1 J = 1-0 silicon monoxide maser emission from 85 stars was resurveyed in 2005 and 2006. The emission from these stars had previously been measured in 1979 and/or 1983. For the detected stars the velocity centroids were determined and compared with the previous values. If supergiant stars, known binary stars, and S Virginis were removed from the data set, 76 sources remained. Seven of these sources were not of sufficient flux density to be claimed as detections. The mean difference in the velocity centroids of the remaining sources was 0.065 km s ^-1, and the standard deviation was 2.00 km s ^-1. It is important to determine the standard deviation of SiO maser time variations in order to identify the level of the time variability of the sources, possible binary stars, unusual emission patterns, or perhaps planets. The velocity centroid of S Virginis differed by 13.5 km s ^-1 from its 1983 value. This difference indicates that S Virginis is probably part of a multiple-star system. A naive analysis of the present data combined with earlier published observations indicates a revolution period of 14.8 yr.