Abundance Determinations for Nova V1974 Cygni 1992 Using the Metropolis Algorithm

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Session 47 -- Nova Cygni 1992
Display presentation, Wednesday, 1, 1994, 9:20-6:30

[47.01] Abundance Determinations for Nova V1974 Cygni 1992 Using the Metropolis Algorithm

Scott J. Austin, Sumner Starrfield (Arizona State University), R. Mark Wagner, Ray Bertram (Ohio State University), Steven N. Shore (Indiana University, South Bend), George Sonneborn (GSFC)

Nova Cygni 1992 was the brightest nova, V$_{max} \approx$4.4, to appear since Nova V1500 Cygni 1975. It is one of the three well studied slow ``neon'' novae, the others being QU Vul, and Nova Pup 1991. We have spectroscopically monitored Nova Cygni 1992 in both the optical (using the OSU CCD spectrograph on the Perkins 1.8-m telescope at Lowell Observatory) and in the UV with IUE. We have done extensive photoionization modeling of the emission line fluxes for epochs 300, 400, and 500 days after maximum. We determined from line diagnostics that the electron density during this time was above the critical densities for many of the observed transitions. Since collisional de-excitations were important, detailed modeling was necessary to determine the physical conditions and elemental abundances of the ejected material. In order to determine both the sensitivity of the abundances to the various model parameters and the uniqueness of our solutions, we mapped the relevant parameter space (Bahcall \& Ulrich 1988, Rev Mod Phys, 60, 297) with the photoionization code CLOUDY 84.06 (Ferland 1993) using the Metropolis algorithm (Metropolis et al. 1953, J Chem Phys, vol. 21). The results have allow us to determine the accuracy of the abundances. Our line profiles show that the ejected material has a non-spherical but axially symmetric configuration. We, therefore, included the filling and covering factors among the parameters in our study and also allowed the density to vary as a function of the radius. Our results demonstrate that the abundances cannot be constrained any better than factors of two but do show that helium, nitrogen, oxygen, and neon are enhanced above solar. Neon and oxygen in particular are shown to be enhanced to the point where an underlying ONeMg white dwarf must be the progenitor.

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