Early evolution of the extraordinary Nova Delphini 2013 (V339 Del)
Authors:
A. Skopal, H. Drechsel, T. Tarasova, T. Kato, M. Fujii, F. Teyssier, O. Garde, J. Guarro, J. Edlin, C. Buil, D. Antao, J.-N. Terry, T. Lemoult, S. Charbonnel, T. Bohlsen, A. Favaro, K. Graham
Image & caption:
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Image caption::
Left panels show the energy distribution in the optical/near-IR spectrum of V339 Del, while the right panels depict a sketch of the corresponding ionization structure of the nova. Top panels are distinctive for the fireball stage, middle panels for the transition to a harder spectrum, and the bottom panels represent evolution when the first X-rays and dust emission were indicated (details are found in Figs. 2 and 9 of the original paper).
Description:
The nova phenomenon results from the explosive thermonuclear fusion of hydrogen to helium in the surface layer of a white dwarf (WD). The hydrogen-rich fuel for this process is accreted on to the WD surface from its binary companion. When the pressure at the base of the accreted layer gets its critical value, protons will create helium cores liberating the light energy of 6.3E+11 Joules from 1 gramm of hydrogen. Current theoretical models of the nova predict that the bolometric luminosity of some novae can exceed for a short time after explosion the so-called Eddington luminosity, at which the light energy balances the gravitational force of the object. Nova Delphini 2013 (V339 Del) was discovered on August 14.6, 2013. Modelling the spectral energy distribution (SED) from its discovery to the first detection of X-rays (day 40) we found that the bolometric luminosity of the nova exceeded the Eddington limit by a factor of 5 to 10. A high cadence of our spectra allowed us to determine duration of the fireball stage to August 20, when the spectrum of the nova changend dramatically. During one day, the maximum SED shifted to the UV domain, whereas in the optical/IR spectrum an extreme increas of the nebular radiation was observed. The corresponding emission measure of 1-2E+62 cmE-3 required the burning WD to generate one order of magnitude higher luminosity than its Eddington value. Our detailed analysis of the nova evolution, from a few hours after its outburst to the first detection of X-rays, showed 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 during and after the fireball stage represent interesting new challenges for the theoretical modelling of the fascinating nova phenomenon.
Reference:
Astronomy & Astrophysics 569, A112, p. 1-14 (2014)
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