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tokens: of a WD (e.g. Shen Bildsten 2007 ; Nomoto et al. 2007 ). The presence of the shell burning prior to the outburst was also suggested by Ramsay et al. (2016) . However, the high accretion rate requires a high mass transfer ratio (i.e. the mass accretion rate divided by the mass-loss rate from the donor). A very efficient wind mass transfer was suggested, for example, by Mohamed Podsiadlowski (2012) , for symbiotic stars with slow and dense winds. Skopal Cariková (2015) suggested that the high wind-mass-transfer efficiency in symbiotic stars can be caused by compression of the wind from their slowly rotating giants. Direct indication of wind focusing was found by Shagatova et al. (2016) for the symbiotic binary SY Mus. To increase the luminosity of the burning WD by a factor of 10, to values observed around the maximum of the 2015 outburst, a transient increase of the accretion rate to is needed to generate the luminosity due to hydrogen burning, where erg g is the energy production of 1 gram of hydrogen due to the nuclear fusion of four protons, and is the hydrogen mass fraction in the accreted matter. The required exceeds the stable-burning limit, which leads to blowing optically thick wind from the WD ( Hachisu et al. 1996 ). The enhanced wind is ionised by the hot WD’s pseudophotosphere, and thus converts a fraction of its stellar radiation to the nebular emission. The corresponding increase of the EM (Fig. 4 ) then causes a relevant brightening in the LC, which we indicate as the outburst (Fig. 2 ). However, the principal question remains as to the origin of this material. Probably, the red giant is responsible for a transient increase of the mass transfer ratio, which temporarily enhances . In general, Bisikalo et al. (2006) found that variations in the velocity of the wind from the giant can cause a disruption of the accretion disk, leading to the infall of a considerable amount of matter ( ) onto the WD surface, thus inducing the outburst. For Z And, Sokoloski et al. (2006) suggested that its 2000-02 outburst was triggered by the influx of hydrogen-rich material from a dwarf-nova-like disk instability at its start that consequently enhanced nuclear shell burning on the WD. 5. Summary We analysed primarily high cadence optical spectroscopy and multicolour photometry obtained prior to and during the first Z And-type outburst of the symbiotic nova AG Peg that began in June of 2015. We determined the fundamental parameters , and of the WD’s pseudophotosphere and its mass-loss rate, , in the course of the outburst (Fig. 7 ). Monitoring the evolution of the He ii 4686 Å, H and the Raman-scattered 6825 Å line profiles allowed us to suggest the ionisation structure of the active hot component in AG Peg (Fig. 12 ) and to outline the nature of its outburst. The main results of our analysis may be summarised as follows. 1. The nova-like outburst of AG Peg terminatedaround 1997 when a wave-like orbitally-related variation in theLC reached its