Formation of the Balmer Line in the Optically Thick Nova Envelope

Abstract

Non–LTE effect and formation of the Balmer line Hα in the optically thick nova wind expected from the radiation–pressure–driven continuous ejection model (cf. Bath and Shaviv, 1976; Ruggles and Bath, 1979) was investigated by use of the pure–hydrogen spherical model atmosphere, in which constant radial expansion velocity, inverse square law of density distribution, and planar grey temperature distribution were assumed. The coupled equations of radiative transfer and statistical equilibrium on the four levels plus continuum model atom (in which Hα line and Balmer–, Paschen–, and Brackett– continua are explicitly treated) were solved by the complete linearization procedure based on the comoving frame method (cf. Mihalas and Kunasz, 1978). We calculated four models as results of the combination of the surface density ρsurf (at ᵀRos = 10−13) (10−12 g/cm3, 10−13 g/cm3) and the expansion velocity Vexp (0 km/sec, 1000 km/sec). We assumed 1012 cm for the photospheric radius rph (at ᵀRos = 1), 10000 K for the effective temperature appearing in the temperature formula, and 100 km/sec for the microturbulent parameter. The low density models have larger extension (rsurf/rph ≃4.1) than the high density ones (rsurf/rph ≃1.7).