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

The results of a high-resolution interferometric campaign targeting the sym biotic long-period variable (LPV) R Aqr are reported. With both near-infrar ed 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 th e cooler circumstellar dust shell. The near-infrared data were taken using aperture-masking interferometry on the Keck I telescope and show R Aqr to b e partially resolved for wavelengths out to 2.2 mu m but with a marked enla rgement, possibly due to molecular opacity, at 3.1 mu m. Mid-infrared inter ferometric measurements were obtained with the Univeristy of California, Be rkeley, infrared spatial interferometer (ISI) operating at 11.15 mu m from 1992 to 1999. Although this data set is somewhat heterogeneous with incompl ete coverage of the Fourier plane and sampling of the pulsation cycle, clea r changes in the mid-infrared brightness distribution were observed, both a s a function of position angle on the sky and as a function of pulsation ph ase. Spherically symmetric radiative transfer calculations of uniform-outfl ow dust shell models produce brightness distributions and spectra which par tially explain the data; however, limitations to this approximation are not ed. 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; ho wever, no clear detection of binarity or of non-LPV elements in the symbiot ic system is reported.