In section 6. Interstellar and circumstellar matter
SPHERE/ZIMPOL observations of the symbiotic system R Aquarii. I. Imaging of the stellar binary and the innermost jet clouds
The symbiotic binary system R Aqr consists of a Mira variable, a hot companion with a spectacular jet outflow, and an extended emission line nebula. The authors observed R Aqr in the Halpha and other filters with the visual camera subsystem ZIMPOL, which is part of the new extreme adaptive optics (AO) instrument SPHERE at the VLT. They analyzed the high resolution ≈ 25 mas images from SPHERE-ZIMPOL and determined the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region 2′′ ( 400 AU) f R Aqr. They resolved for the first time the R Aqr binary and found that the jet source is 46 ± 1 mas west (position angle −85.5◦ ± 1.0◦) of the Mira star. The central jet source is the strongest Hα component. Within 0.5′′ (100 AU) in the SW of the central source, they observed a string of bright clouds arranged in a zig-zag pattern, and further out, at 1′′ − 2′′, fainter and more extended bubbles. In the N and NE they found a bright, very elongated filamentary structure between 0.2′′ − 0.7′′ and faint perpendicular “wisps” further out. Cloud densities are very high, implying a short recombination timescale of a year or less.