First results from the Faint Object Camera: Imaging the core of R Aquarii

The Faint Object Camera on the Hubble Space Telescope was used to observe the inner regions of the symbiotic Mira variable R Aquarii through two filters centered on the [O III] 5007 Å and the [O II] 3727 Å nebular emission lines. Both images show bright arcs, knots, and filaments superposed on fainter, diffuse nebulosity extending in a general SW-NE direction from the Mira variable to the edge of the field at 10″ distance. The observed nebulosity is brighter and more complex in its northern extension where it attains a surface brightness of order 10 -12 ergs cm -2 s -1 arcsec -2 in the [O III] line. Although saturated due to the strong signal, the core is resolved in both lines into at least two bright knots of emission whose positions and structure are aligned with PA = 50°. The central knots appear to be the source of a continuous, well-collimated, stream of material extending out to 3″-4″ in the northern sector corresponding to a linear distance of approximately 1000 AU. The northern stream seems to bend around an opaque obstacle and form a spiral before breaking up into discrete wisps and knots deviating toward the north. The southern stream is composed of smaller, discrete parcels of emitting gas curving to the SE. A preliminary estimate of the [O III]-to-[O II] line ratio in the filaments shows that it is significantly higher than 1 indicating either that the features are density-bounded or that the ionizing radiation field has a nonthermal power-law form.