Early evolution of the extraordinary Nova Delphini 2013 (V339 Del)

Aims. We determine the temporal evolution of the luminosity (L-wD), radius (R-WD) and effective temperature (T-eff) of the white dwarf (WD) pseudophotosphere of V339 Del from its discovery to around day 40. Another main objective was studying the ionization structure of the ejecta. Methods. These aims were achieved by modelling the optical/near-IR spectral energy distribution (SED) using low-resolution spectroscopy (3500-9200 A), LIBVRck and JHKLM photometry. Important insights in the physical conditions of the ejecta were gained from an analysis of the evolution of the Ha and Raman-scattered 6825 A 0 VI line using medium-resolution spectroscopy (R similar to 10000). Results. During the fireball stage (Aug. 14.8-19.9, 2013). 114 was in the range of 6000-12 000 K, Rwp was expanding non-uniformly in time from similar to 66 to similar to 300 (d/3 kpc)R-circle dot, and LwD was super-Eddineton, but not constant. Its maximum of similar to 9 x 10(38) (d/3 kpc)(2) erg s(-1) occurred around Aug. 16.0, at the maximum of Tett, half a day before the visual maximum. After the fireball stage, a large emission measure of 1.0-2.0 x10(62) (d/3 kpc)(2) cm(-3) constrained the lower limit of Lvo to be well above the super-Eddington value. The mass of the ionized region was a few x10(-4) M-circle dot and the mass-loss rate was decreasing from similar to 5.7 (Aug. 22) to similar to 0.71 x 10(-4) M-circle dot, yr(-1) (Sept. 20). The evolution of the h alpha line and mainly the transient emergence of the Raman-scattered 0 VI 1032 A line suggested a biconical ionization structure of the ejecta with a disk-like HI region persisting around the WD until its total ionization, around day 40. On Sept. 20 (day 35), the model SED indicated a dust emission component in the spectrum. The dust was located beyond the HI zone, where it was shielded from the hard, >= 10(5) K. radiation of the burning WD at that time. Conclusions. Our extensive spectroscopic observations of the classical nova V339 Del allowed us to map its evolution from the very early phase after its explosion. It is evident that the nova was not evolving according to the current theoretical prediction. The unusual non-spherically symmetric ejecta of nova V339 Del and its extreme physical conditions and evolution dining and after the fireball stage represent interesting new challenges for the theoretical modelling of the nova phenomenon.