R Aquarii: The Large-Scale Optical Nebula and the Mira Variable Position

The R Aquarii symbiotic star system is surrounded by a large-scale optical nebula. The authors present observations of the nebular [O III] structure and discuss its morphological significance in context with previously observed small-scale radio-continuum features, which may be related. They suggest that a precessing accretion disk may explain the global features of both the large-scale optical emission and the small-scale radio emission. Moreover, the authors have determined an accurate position of the system's Mira, which suggests that a recent theoretical model, yielding an egg-shaped central H II region for symbiotic systems with certain physical parameters, may apply to R Aquarii. The optical position of the 387^d period Mira variable is consistent with the authors' previous findings in the radio, that SiO maser emission is far removed from the Mira photosphere.