Ultraviolet Spectroscopic Study of BY Circini and V 1425 Aquilae from IUE Satellite

We present the ultraviolet spectra of two classical novae, BY Circini 1995 and V1425 Aquilae 1995, using observations obtained with the International Ultraviolet Explorer (IUE). The outflow velocity of the ionized ejecta was calculated to be 2100–2700 km s −1 and 1600–1900 km s −1 (FWHM) for BY Cir and V1425 Aql, respectively. The models generated by Jose & Hernanz ( 1998 , ApJ , 494 , 680) indicate that BY Cir is a CO4/CO5 nova with WD mass of ∼1.15 M ⊙ , while V1425 Aql is a CO2/CO3 nova with WD mass of ∼0.9 M ⊙ . Different profiles of BY Cir and V1425 Aql showing variations of line fluxes at different orbital phases are presented. This paper focuses on the calculated spectral line fluxes for the N III emission line at 1750 Å and the C III emission line at 1909 Å, produced in the expanding shell of ionized gas. Our results show that there are variations of line fluxes with time. We attribute these spectral variations in line fluxes to the variations of both density and temperature in the line-emitting regions as a result of the inhomogeneous ejecta. The variable line fluxes, ultraviolet luminosities and accretion rates support a model of the ejecta consisting of an optically thin dust shell and hot ionized gas.