Spectral evolution of the two classical novae PW Vul and V1668 Cyg using International Ultraviolet Explorer low‐resolution spectra

Abstract

We studied the evolution of the normalized flux of selected ultraviolet (UV) emission lines of two classical novae (PW Vul and V1668 Cyg) using International Ultraviolet Explorer (IUE) short wavelength observations. Different phases of the outburst are studied. Emission lines covering a wide range of ionization states are investigated. We use the calculated fluxes to estimate the mass accretion rates during quiescence of both novae. We found average values of the UV luminosity for PW Vul to be of 1.0 ± 0.1 × 10 35 erg s −1 , and the corresponding value for V1668 Cyg is 4.0 ± 0.2 × 10 35 erg s −1 . In quiescence, we obtained average values for the mass accretion ratesṀ acc of 8.7 ± 0.4 × 10 −10 M ⊙ year −1 and 1.8 ± 0.1 × 10 −10 M ⊙ year −1 , respectively. We attribute the spectral behavior of the two systems to the variation of the optical thickness and temperature of the envelope during the different phases of the outburst. Our results demonstrate the effect of the white dwarf mass on the evolution of the nova. The results of IUE observations are consistent with the theoretical CO models of classical nova of.