RS-OPH AT DAY-201 - A TEST-CASE FOR SHOCKS IN NOVA SHELLS

We have applied a shock model to the nebula ejected in 1985 by the rec urrent nova RS Oph. The model, based on the SUMA code, matches the rel ative line intensities observed at day 201 after outburst and yields e lement abundances relative to hydrogen, density and temperature profil es throughout the shocked region, and integrated fluxes in all ranges of the spectrum. We have investigated the effect of dust and the contr ibution of a hot star as an additional photoionization source. We find that the entire spectrum is well explained by shocks, even neglecting any other photoionizing source. In particular, the residual X-ray emi ssion detected more than 200 d after outburst can be the result of sho cks. The estimated distance of the shock front from the central star i s of the order of 5 x 10(15) cm. The high helium abundance, as well as the very low oxygen abundance resulting from this model, is shown to agree with the thermonuclear runaway scenario for recurrent novae, whi ch involves accretion on to a very massive white dwarf.