Optical spectroscopy of the recurrent nova RS Ophiuchi – from the outburst of 2006 to quiescence

Abstract

Optical spectra of the 2006 outburst of RS Ophiuchi beginning one day after\ndiscovery to over a year after the outburst are presented here. The spectral\nevolution is found to be similar to that in previous outbursts. The early phase\nspectra are dominated by hydrogen and helium (I & II) lines. Coronal and\nnebular lines appear in the later phases. Emission line widths are found to\nnarrow with time, which is interpreted as a shock expanding into the red giant\nwind. Using the photoionisation code CLOUDY, spectra at nine epochs spanning 14\nmonths after the outburst peak, thus covering a broad range of ionisation and\nexcitation levels in the ejecta, are modelled. The best-fit model parameters\nindicate the presence of a hot white dwarf source with a roughly constant\nluminosity of 1.26 x 10^{37} erg/s. During first three months, the abundances\n(by number) of He, N, O, Ne, Ar, Fe, Ca, S and Ni are found above solar\nabundances; abundances of these elements decreased in the later phase. Also\npresented are spectra obtained during quiescence. Photoionisation model of the\nquiescence spectrum indicates the presence of a low luminosity accretion disk.\nThe helium abundance is found to be subsolar at quiescence.\n