We present an analysis of optical and infrared spectra of the recurrent nova RS Oph obtained during between 2006 and 2009 .
The best fit to the optical spectrum for 2006 September 28 gives T _ { eff } = 3900 K for \log { g } = 2.0 , while for \log { g } = 0.0 we find T _ { eff } = 4700 K , and a comparison with template stellar spectra provides T _ { eff } \sim 4500 K. The observed spectral energy distribution ( SED ) , and the intensities of the emission lines , vary on short ( \raisebox { -2.58 pt } { $ \stackrel { \raisebox { -0.86 pt } { $ \textstyle < $ } } { \sim } $ } 1 day ) time-scales , due to disc variability .
We invoke a simple one-component model for the accretion disc , and a model with a hot boundary layer , with high ( \sim 3.9 \times 10 ^ { -6 } M _ { \odot } yr ^ { -1 } ) and low ( \sim 2 \times 10 ^ { -8 } M _ { \odot } yr ^ { -1 } ) accretion rates , respectively .
Fits to the accretion disc-extracted infrared spectrum ( 2008 July 15 ) yield effective temperatures for the red giant of \mbox { $T _ { eff } $ } = 3800 \pm 100 K ( \log { g } = 2.0 ) and \mbox { $T _ { eff } $ } = 3700 \pm 100 K ( \log { g } = 0.0 ) .
Furthermore , using a more sophisticated approach , we reproduced the optical and infrared SEDs of the red giant in the RS Oph system with a two-component model atmosphere , in which 90 % of the surface has T _ { eff } = 3600 K and 10 % has T _ { eff } = 5000 K. Such structure could be due to irradiation of the red giant by the white dwarf .