Near- and mid-infrared subarcsecond structure of the dusty symbiotic star R Aquarii

The results of a high-resolution interferometric campaign targeting the symbiotic long-period variable (LPV) R Aqr are reported. With both near-infrared measurements on baselines out to 10 m and midinfrared data extending to 32 m, we have been able to measure the characteristic sizes of regions from the photosphere of the LPV and its extended molecular atmosphere out to the cooler circumstellar dust shell. The near-infrared data were taken using aperture-masking interferometry on the Keck I telescope and show R Aqr to be partially resolved for wavelengths out to 2.2 mu m but with a marked enlargement, possibly due to molecular opacity, at 3.1 mu m. Mid-infrared interferometric measurements were obtained with the Univeristy of California, Berkeley, infrared spatial interferometer (ISI) operating at 11.15 mu m from 1992 to 1999. Although this data set is somewhat heterogeneous with incomplete coverage of the Fourier plane and sampling of the pulsation cycle, clear changes in the mid-infrared brightness distribution were observed, both as a function of position angle on the sky and as a function of pulsation phase. Spherically symmetric radiative transfer calculations of uniform-outflow dust shell models produce brightness distributions and spectra which partially explain the data; however, limitations to this approximation are noted. Evidence for significant deviation from circular symmetry was found in the mid-infrared and more tentatively at 3.08 mu m in the near-infrared; however, no clear detection of binarity or of non-LPV elements in the symbiotic system is reported.