The Evolution of the 7.5 -- 13 $\mu$m Spectrum of Nova Cygni 1992
Session 53 -- Recent Observational Results on Nova Cygni 1992
Oral presentation, Wednesday, 1, 1994, 2:00-5:30

## [53.07] The Evolution of the 7.5 -- 13 $\mu$m Spectrum of Nova Cygni 1992

T.L. Hayward, J.R. Houck (Cornell University), J.W. Miles (National Air and Space Museum)

We have observed Nova Cygni 1992 at 7 epochs using Cornell's SpectroCam-10 camera/spectrograph on the 200-inch Hale telescope. Low-resolution ($\lambda/\Delta\lambda \approx 100$) spectra spanning 7.5 -- 13.5~$\mu$m were taken on each date. The free-free continuum, hydrogen recombination line, and [Ne~II] 12.8~$\mu$m emission observed in April 1992 declined through January 1993, by which time even the [Ne~II] emission was undetectable. Between August and November 1992 a strong [Ne~VI] 7.66~$\mu$m coronal line appeared, accompanied by a weaker [Ar~III] 8.99~$\mu$m feature. Remarkably, subsequent observations showed that these lines remained nearly constant in intensity through October 1993, our most recent observation. Medium-resolution ($\lambda/\Delta\lambda \approx 2000$) spectra of the [Ne~II] line showed that a double-peaked profile with FWHM $\approx$ 2200 km s$^{-1}$ observed in April 1992 changed to a flat-topped shape by August, similar to the shape of optical lines. The [Ne~VI] line exhibited a similar width in both November 1992 and October 1993. Our data show no evidence for dust at any epoch. We will discuss the implications of our unique data set on the dynamics, ionization structure, and elemental abundances of the nova shell.