COMPARISONS OF SIO MASER AND LONG-PERIOD VARIABLE POSITIONS IN THE R-AQUARII AND OMICRON CETI BINARY-SYSTEMS

We have determined that the absolute position of the centroid of SiO maser-emitting spots toward both R Aqr and o Cet are coincident with the position of the long-period variables (LPVs) in these binary systems to within the errors of measurement. The SiO positions were determined with the Hat Creek interferometer, while the LPV positions were determined with the 8 inch (20 cm) transit circle of the US Naval Observatory. These results contradict an earlier report of a circumbinary SiO maser far removed from the LPV in the R Aqr binary system, and we suggest statistical reasons for the discrepancy. We present high-resolution spectra of both sources and discuss possible models.