A NEW SPECTROSCOPIC ORBIT FOR RS OPHIUCHI

This paper presents a new spectroscopic orbit for the recurrent nova R S Ophiuchi. We analyze echelle spectra obtained during quiescence; som e spectra resemble those of A-type stars and some resemble M giant spe ctra. We derive an orbital period of 460 days for both A-type and M-ty pe absorption features. The A-type features are 0.4P out of phase with the orbit of the M giant. We consider models in which the A-type feat ures can be associated with a hot companion to the M giant, the heated hemisphere of the red giant, or some other component in a binary syst em. RS Oph is best understood if the A-type features are not associate d with either binary component. Our analysis of the orbit and the opti cal light curve indicates the system has an inclination of 30 degrees- 40 degrees if the hot component is a Chandrasekhar mass white dwarf.