Near-infrared H- and K-band studies of the 2006 outburst of the recurrent nova RS Ophiuchi

We present near-infrared photospectroscopy in the H and K bands of the 2006 outburst of the recurrent nova RS Ophiuchi. The observations cover the period between 1 and 94 d after the eruption. The near-infrared light curve is presented. An extensive set of spectra is presented, lines identified and the general characteristics of the spectra discussed. Analysis of the H  i line profiles shows the presence of broad wings on both flanks of a strong central component indicating the presence of a bipolar velocity flow in the ejecta. Such a flow is kinematically consistent with the bipolar structure that the object displays in high-resolution spatial images. We discuss the behaviour and origin of the Fe  ii lines at 1.6872 and 1.7414 μm that are prominently seen throughout the span of the observations. It is examined and shown that Lyman α and Lyman continuum fluorescence are viable mechanisms to excite these lines. We draw upon the result, that collisional excitation can also contribute in exciting and significantly enhancing the strength of these Fe  ii lines, to propose that these lines originate from a site of high particle density. Such a likely site could be the high-density, low-temperature contact surface that should exists in the shock front in between the shocked ejecta and red giant wind. Recombination analysis of the H  i lines indicates deviations from case B conditions during most of the span of our observations indicating optical depth effects. It appears likely that the breakout of the shock front had not yet occurred till the end of our observations. An analysis is made of the temporal evolution of the Si  vi ] 1.9641 μm coronal line and another coronal line at 2.0894 μm which is attributed to Mn  xiv ]. Assuming collisional effects to dominate in the hot coronal gas, estimates are made of the ion temperature in the gas.