Spitzer and Ground-based Infrared Observations of the 2006 Eruption of RS Ophiuchi

We present Spitzer Space Telescope and complementary ground-based infrared observations of the recurrent nova RS Ophiuchi, obtained over the period 64-111 days after the 2006 eruption. The Spitzer IRS data show a rich emission-line spectrum superimposed on a free-free continuum. The presence of fine-structure and coronal infrared lines lead us to deduce that there are at least two temperatures (1.5 × 10 5 and 9 × 10 5 K) in the ejecta/wind environment and that the electron density in the "cooler" region is 2.2 × 10 5 cm -3 . The determination of elemental abundances is not straightforward, but on the assumption that the Ne and O fine-structure lines arise in the same volume of the ejecta, the O/Ne ratio is ≳0.6 by number.