SOFIA/FORCAST Observations of the Symbiotic Mira, R Aquarii

The FORCAST instrument on the Stratospheric Observatory for Infrared Astronomy (SOFIA) was used to observe the symbiotic Mira, R Aquarii (R Aqr) in September 2016. Images through several filters at wavelengths from 6.4 to 37.1 mu-m, and a grism spectrum covering 8.4 to 13.7 mu-m were obtained. R Aqr consists of an AGB star and a hot white dwarf in an eccentric binary orbit, an accretion flow onto the white dwarf, and the resulting jet. The images show a point source (~3.5" PSF at 37 mu-m) with the observed emission dominated by the dusty AGB star. The SOFIA data were obtained when the Mira phase was about 0.4 (minimum at phase 0.5) and the V magnitude was about 10. The measured fluxes range from about 700 Jy at the shorter wavelengths to about 80 Jy at 37 mu-m. These are a factor of 2 lower than the fluxes measured by ISO in May 1996, when the Mira phase was close to maximum and the V magnitude was about 8. We discuss the differences between the ISO and FORCAST measurements of the spectral energy distribution in the context of our proposed monitoring of the R Aquarii system with SOFIA as it approaches eclipse and periastron in its ~44 year orbit.