Infrared space observatory and ground-based infrared observations of the classical Nova V723 Cassiopeiae

We present observations of the classical nova V723 Cassiopeiae (Nova Cas 1995), obtained both with the Infrared Space Observatory (ISO) and from the ground. The infrared spectrum was dominated in the first year by H and He recombination lines, and at later times by coronal lines. The H recombination lines imply a reddening of E(B- V) = 0.78, an electron temperature of 7000 K, and an electron density of 2 × 10 ⁸ cm ^-3 on day 250. We argue that the high-ionization species in the infrared are most likely the result of collisional ionization rather than photoionization and are therefore truly "coronal"; we estimate a temperature of 3.2 × 10 ⁵ K in the coronal region and abundance ratios of S/Si ≃ 2.1, Ca/Si ≃ 1.6, and Al/Si ≃ 1.5. The ejected mass as determined from the Brα line was 2.6 × 10 ^-5 M⊙ for a distance of 4 kpc; however, the mass deduced from the free-free emission, which we conclude arises primarily in the coronal zone, is 4.3 × 10 ^-4 M⊙ V723 Cas did not display the [O IV] 25.89 μm fine-structure line, which was typically seen in the spectra of novae observed with ISO. There was no evidence of dust emission in V723 Cas.