Modelling the spectral energy distribution of the red giant in RS Ophiuchi: evidence for irradiation
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 Teff 3900 K for log g 2.0, while for log g 0.0 we find Teff 4700 K, and a comparison with template stellar spectra provides Teff 4500 K. The observed spectral energy distribution (SED) and the intensities of the emission lines, vary on short (1 d) 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 ~3.9 x 10 6M yr 1) and low ~2 x 10 8M yr 1) accretion rates, respectively. Fits to the accretion disc extracted infrared spectrum (2008 July 15) yield effective temperatures for the red giant of Teff 3800 100 K (log g 2.0) and Teff 3700 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 twocomponent model atmosphere, in which 90 per cent of the surface has Teff 3600 K and 10 per cent has Teff 5000 K. Such structure could be due to irradiation of the red giant by the white dwarf. (c) 2015 The Authors.