High-resolution infrared spectroscopy of R Aquarii

A time series of high-resolution 1.5-2.5 micron spectra of the symbiotic Mira variable R Aquarii has been observed over the last decade. As expected, the spectra reveal only lines originating the Mira. The photospheric spectrum of the Mira appears totally normal. Velocity, excitation temperature, and column density information are presented as a function of phase. The pulsation of the Mira observed in the infrared is very regular, allowing orbital velocity changes to be searched for at the few km/s level. The data show that, assuming a semiamplitude greater than about 1 km/s, the orbital period must be either between 18 and 21 yr or longer than 32 yr. The derived orbit is highly uncertain but the data are consistent with a rather elliptical orbit of long period. If the derived orbit is valid, the size of the Roche lobe surrounding the Mira becomes small enough at periastron to influence the atmosphere of the Mira. (Author)