Context. AG Peg is known as the slowest symbiotic nova, which experienced its nova-like outburst around 1850. After 165 years, during June of 2015, it erupted again showing characteristics of the Z And-type outburst. Aims. The primary objective is to determine basic characteristics, the nature and type of the 2015 outburst of AG Peg. Methods. We achieved this aim by modelling the spectral energy distribution using low-resolution spectroscopy (330-750 nm; R = 500-1000), medium-resolution spectroscopy (420-720 nm; R ∼ 11000), and U BVR C I C photometry covering the 2015 outburst with a high cadence. Optical observations were complemented with the archival HST and FUSE spectra from the preceding quiescence. Results. During the outburst, the luminosity of the hot component was in the range of 2-11×10 37 (d/0.8 kpc) 2 erg s −1 , being in correlation with the light curve (LC) profile. To generate the maximum luminosity by the hydrogen burning, the white dwarf (WD) had to accrete at ∼ 3 × 10 −7 M ⊙ yr −1 , which exceeds the stable-burning limit and thus led to blowing optically thick wind from the WD. We determined its mass-loss rate to a few ×10 −6 M ⊙ yr −1 . At the high temperature of the ionising source, 1.5 − 2.3 × 10 5 K, the wind converted a fraction of the WD's photospheric radiation into the nebular emission that dominated the optical. A one order of magnitude increase of the emission measure, from a few ×10 59 (d/0.8 kpc) 2 cm −3 during quiescence, to a few ×10 60 (d/0.8 kpc) 2 cm −3 during the outburst, caused a 2 mag brightening in the LC, which is classified as the Z And-type of the outburst. Conclusions. The very high nebular emission and the presence of a disk-like H i region encompassing the WD, as indicated by a significant broadening and high flux of the Raman-scattered O vi 6825 Å line during the outburst, is consistent with the ionisation structure of hot components in symbiotic stars during active phases.

A new fiber-fed spectrograph was installed at the 60 cm telescope of the Stará Lesná Observatory. The article presents tests of its performance (spectral resolution, signal-to-noise ratio, radial-velocity stability) and reports observations of selected variable stars and exoplanet host stars. First test observations show that the spectrograph is an ideal tool to observe bright eclipsing and spectroscopic binaries but also symbiotic and nova-like stars. The radial-velocity stability (60-80 m s −1 ) is sufficient to study spectroscopic binaries and to detect easily the orbital motion of hot-Jupiter extrasolar planets around bright stars.

Context. AG Draconis produces a strong supersoft X-ray emission. The X-ray and optical/UV fluxes are in strict anticorrelation throughout the active and quiescent phases. Aims. We identify the source of the X-ray emission and reveal the nature of the observed flux anticorrelation. Methods. We used X-ray and UV observations with XMM-Newton, far-UV spectroscopy from FUSE, low-and high-resolution IUE spectra, and optical/near-IR spectroscopic and/or photometric observations. We modeled the spectral energy distribution and broad wings of the O vi λ1032, λ1038 and He ii λ1640 lines by the electron-scattering during the maximum of the 2003 burst, and the subsequent transition and quiescent phase. Results. The X-ray-near-IR energy distribution at different levels of the star's brightness confirmed the observed flux anticorrelation quantitatively and showed that the optical bursts are associated to an increase in the nebular component of radiation. The profile-fitting analysis revealed a significant increase in the mean particle density around the hot star from ∼2.6 × 10 10 cm −3 during quiescent phase to ∼1.1 × 10 12 cm −3 during the burst. Conclusions. The supersoft X-ray emission is produced by the white dwarf photosphere. The X-ray and far-UV fluxes make it possible to determine its temperature unambiguously. The supersoft X-ray-optical/UV flux anticorrelation is caused by the variable wind from the hot star. The enhanced hot star wind gives rise to the optical bursts by reprocessing high-energy photons from the Lyman continuum to the optical/UV.