The Optical Spectroscopic Evolution of V1974 Cygni (Nova Cygni 1992)

Abstract

Optical observations of nova V1974 Cygni (Cygni 1992), spanning a 4 year period, have been used to study its spectroscopic evolution. The data cover a wavelength range from $\sim 3200 - 8000$ \AA and follows the nebular evolutionary phase of the ejecta. We have modeled the integrated fluxes by means of the photoionization code CLOUDY. The models were run at a {\it fixed} abundance value for the most prominent elements (i.e. H, He, C, O, N, Ne, Fe, etc) over the entire time sequence. It is possible to constrain from this simple model some of the physical conditions of the gaseous emitting region, like temperature and density. Compared with previous studies of the gas abundances of the heavy elements, we found that smaller enhancements of S, N and Ar, and comparable values for O and Fe, are able to reproduce the observations. The time evolution of the surface temperature of the ionizing source and the high-ionization iron lines [Fe VII] 6087 \AA and [Fe X] 6374 \AA, is similar to what it is observed in the soft X-rays. The early line profiles can be reproduced using a simple kinematical model consisting of an equatorial ring and polar caps, expanding at a velocity of $\sim 1100$ km/s. This simple model also approximates the structure of the resolved shell observed by HST. Considering the complicated structure of the shell, the lack of well defined values of its gas density and our limited knowledge of the time evolution of the surface temperature of the photoionization source, the comparison between models and observations agrees remarkably well.Comment: 14 text pages, 12 figure

Envelope models for the supersoft X-ray emission of V1974 Cyg

“…Using mid-infrared spectroscopy, Hayward et al (1996) determined X = 0.30, very close to the value in our ONe50 models. Later works (Moro-Martín et al 2001;Vanlandigham et al 2002) determined smaller metal enhancements than Austin et al (1996), which also agrees with a hydrogen abundance higher than X = 0.18.…”

New Elemental Abundances for V1974 Cygni

“…The two other analyses in the literature (Hayward et al 1996;Moro-Martín et al 2001) based their work on the results of A96 and propagated this error into their work. Because there is such a large parameter space, and because many of the parameters are interdependent, it is difficult to determine whether a solution to one set of spectra is unique.…”

“…Three detailed abundance analyses have been carried out for Cyg 92: Austin et al (1996, hereafter A96), Hayward et al (1996), and Moro-Martín et al (2001). Unfortunately, these analyses were based on data that were dereddened incorrectly.…”

M31N 2008-12a—THE REMARKABLE RECURRENT NOVA IN M31: PANCHROMATIC OBSERVATIONS OF THE 2015 ERUPTION

“…While late-time spectra are required to confirm what is causing such a trend, it is likely to be line driven. Nebular lines typically begin to appear in nova spectra once the UV becomes optically thin (see, for example, Moro-Martín et al 2001;Della Valle et al 2002, which is also related to the unveiling of the SSS). The strongest nebular lines in novae are usually the [O III] (particularly 4959/5007 Å) lines, located within the V-band.…”