Abstract:
Optical spectra of the 2006 outburst of RS Ophiuchi beginning one day after discovery
to over a year after the outburst are presented here. The spectral evolution is found to be
similar to that in previous outbursts. The early-phase spectra are dominated by hydrogen and
helium (I and II) lines. Coronal and nebular lines appear in the later phases. Emission line
widths are found to narrow with time, which is interpreted as a shock expanding into the
red giant wind. Using the photoionization code CLOUDY, spectra at nine epochs spanning 14
months after the outburst peak, thus covering a broad range of ionization and excitation levels
in the ejecta, are modelled. The best-fitting model parameters indicate the presence of a hot
white dwarf source with a roughly constant luminosity of 1.26 × 1037 erg s−1. During the first
three months, the abundances (by number) of He, N, O, Ne, Ar, Fe, Ca, S and Ni are found to
be above solar abundances; the abundances of these elements decreased in the later phase. Also
presented are spectra obtained during quiescence. A photoionization model of the quiescent
spectrum indicates the presence of a low-luminosity accretion disc. The helium abundance is
found to be subsolar at quiescence.
