The 1985 outburst of RS Ophiuchi: spectroscopic results

Abstract

Optical spectroscopic data on the recurrent nova RS Ophiuchi obtained between 32 and 108 days after its last outburst on 1985 January 27 are presented. RS Oph was in the coronal-line phase at that time. The widths of the permitted as well as coronal-lines decreased continuously. Assuming that the ejected envelope decelerated due to its interaction with circum stellar matter, its size is deduced as a function of time. Observed fluxes in permitted lines would then imply that the electron density decreased from 3 × 10 ⁹ cm ^#x2212;3 on day 32 to 1.8 × 10⁸ cm^-3 on day 108, for an assumed filling factor of 0.01. The helium abundance in the ejecta is estimated to be n(He)/n(H) ∼ 0.16. The mass of the unshocked ejecta was 3 × 10^-6 (Φ/0.01)^1/2M☉, (at this stage, where f is the filling factor. Observed fluxes in coronal-lines imply that the temperature of coronal-line region decreased from 1.5 × 10⁶ K on day 32 to 1.1 × 10⁶ K on day 108. Most of the coronal line emission, as well as He n emission arises in shocked and cooling ejecta. This region is not isothermal, but contains material at a wide range of temperatures. Mass of the shocked ejecta is estimated to be in the range 10−7−10^-6M☉ Based on the number of H- and He-ionizing photons, we estimate that the ionizing source evolved from a radius and temperature of (2 × l0¹² cm, 3 × 10⁴ K) on day 32 to (6 × l0⁹ cm, 3.6 × 10⁵K) on day 204. We also present the spectra of RS Oph recorded in quiescent phase, 2 and 3 years after outburst, for comparison. The spectrum is dominated by that of M2 giant secondary, with superposed emission lines of H and He I.