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

TL;DR

This study presents optical spectral observations of RS Ophiuchi's 2006 outburst, modeling its evolution over 14 months and during quiescence, revealing shock expansion, elemental abundance changes, and accretion disk presence.

Contribution

It provides detailed spectral analysis and photoionisation modeling of RS Ophiuchi's outburst and quiescence, highlighting elemental abundance variations and accretion disk characteristics.

Findings

Spectral evolution similar to previous outbursts.

Shock expansion inferred from narrowing emission lines.

Elemental abundances decrease over time.

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 & 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 photoionisation code CLOUDY, spectra at nine epochs spanning 14 months after the outburst peak, thus covering a broad range of ionisation and excitation levels in the ejecta, are modelled. The best-fit model parameters indicate the presence of a hot white dwarf source with a roughly constant luminosity of 1.26 x 10^{37} erg/s. During first three months, the abundances (by number) of He, N, O, Ne, Ar, Fe, Ca, S and Ni are found above solar abundances; abundances of these elements decreased in the later phase. Also presented are spectra obtained during quiescence. Photoionisation model of the quiescence spectrum indicates the presence of a low luminosity accretion disk. The helium abundance is found to be subsolar at quiescence.