tokens: line profiles. Calculations of lines formed in disc winds from white-dwarf stars have been limited to resonance lines tend to produce absorption profiles for inclinations i ≳ 70° (Proga et al. 2002 ). However, disc-wind models for T Tauri stars can produce similar H α line profiles to those seen in RS Oph (Kurosawa, Harries Symington 2006 ). Polarization measurements may be able to distinguish between inflow and outflow models, since, in the inflow models, the fraction of scattered light contributing to the blue wing is larger. 4 SODIUM ABSORPTION LINES 4.1 Na <sc>i</sc> <sc>D lines in RS Oph</sc> Sodium absorption lines have been suggested as a useful diagnostic of the circumstellar environment in both supernovae and their progenitor systems (Patat et al. 2007 ; Chugai 2008 ; Patat et al. 2011 ). The Na i D lines, together with other strong metal lines such as the Ca ii H K lines, probe the density and ionization conditions in the circumstellar environment. We modelled the line profiles expected from the simulations, with the aim of understanding where the observed features in RS Oph form in the CSM and whether the same circumstellar components can be responsible for metal line variations observed in some SN Ia. We have modelled Na i D absorption line profiles directly from the simulations, using the results from the ionization calculation described above. All neutral sodium atoms are assumed to be in the ground state and contribute to the absorption lines. We present line profiles from calculations in which the mass-loss rate has been scaled to 5 × 10 −7 M ⊙ yr −1 , since this gives better agreement with observations both for the ionization structure and the line profiles. We did not include a detailed treatment for the H ii region in the Na i D line ionization calculation; instead, we neglected the contribution from all material within 3 × 10 13 cm. The results are not particularly sensitive to this choice of radius. We assume that the continuum flux around the Na i D lines is dominated by the RG. The presence of an emission component in RS Oph limits the extent to which this is true (Patat et al. 2011 ). The emission component has a width v ∼ 100 km s −1 , higher than the width of the absorption lines, and is likely associated with emission from the ionized region. The line profiles were derived by calculating the optical depth to the photosphere along lines of sight through the CSM. The photosphere was subdivided into lines of sight to ensure that the substructure along the line of sight is resolved. Finally, the flux from each line of sight was combined and weighted by area. Fig. 6 shows the resulting synthetic line profiles. For inclinations i ≳ 70°, the line profile shows both red and blueshifted components. The redshifted components arise in the wind that is falling back on to the white dwarf and accretion disc, and is therefore strongest when the white dwarf is closest to the observer and the line of sight intersects the most
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