A Multiwavelength Light-curve Model of the Classical Nova V339 Del: A Mechanism for the Coexistence of Dust Dip and Supersoft X-Rays

The classical nova V339 Del 2013 is characterized by a 1.5 mag dip of the V light curve owing to a dust shell formation, with which soft X-ray emissions coexist. We present a Stromgren y-band light curve, which represents continuum emission, not influenced by strong [O III] emission lines. The y light curve monotonically decreases in marked contrast to the V light curve that shows a 1.5 mag dip. We propose a multiwavelength light-curve model that reproduces the y and V light curves as well as the gamma-ray and X-ray light curves. In our model, a strong shock arises far outside the photosphere after optical maximum, because later ejected matter collides with earlier ejected gas. Our shocked shell model explains optical emission lines, H alpha, hard X-ray, and gamma-ray fluxes. A dust shell forms behind the shock that suppresses [O III]. This low flux of [O III] shapes a 1.5 mag drop in the V light curve. Then, the V flux recovers with an increasing contribution from [O III] lines, while the y flux does not. However, the optical depth of the dust shell is too small to absorb the photospheric (X-ray) emission of the white dwarf. This is the reason that a dust shell and soft X-ray radiation coexist. We determined the white dwarf mass to be M-WD = 1.25 +/- 0.05 M-circle dot and the distance modulus in the V band to be (m - M)(V) = 12.2 +/- 0.2; the distance is d = 2.1 +/- 0.2 kpc for the reddening of E(B - V) = 0.18.