A. Skopal

The symbiotic star CH Cygni — I. Non-thermal bipolar jets

ABSTRA C T Very Large Array surface brightness and spectral index maps of the evolving extended emission of the triple symbiotic star CH Cygni are presented. These are derived from observations at 4.8, 8.4 and 14 GHz between 1985 and 1999. The maps are dominated by thermal emission around the central bright peak of the nebula, but we also find unambiguous non-thermal emission associated with the extended regions. Our observations confirm that this is a jet. The central region has been associated with the stellar components through Hubble Space Telescope imaging. If the jets are the result of ejection events at outburst, expansion velocities are consistent with those from other measurement methods. We propose that the non-thermal emission is caused by material ejected in the bipolar jets interacting with the circumstellar wind envelope. The resulting shocks lead to local enhancements in the magnetic field from the compact component of the order of 3 mG.

Structure of the hot object in the symbiotic prototype Z Andromedae during its 2000-03 active phase

Aims. To investigate structure of the hot object in the symbiotic prototype Zu2009And during its major 2000-03 active phase. Methods. Analysis of the far ultraviolet, optical low- and high-resolution spectroscopy and

The origin of the supersoft X-ray-optical/UV flux anticorrelation in the symbiotic binary AG Draconis

{it UBVR}

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

xa0photometry. Reconstruction of the spectral energy distribution (SED) during the outburst. The Raman scattering process. Results. At the initial stages of the outburst the hot object was characterized by the two-temperature spectrum (a warm stellar radiation and a strong nebular emission) with signatures of a mass-outflow at moderate (~100-200u2009kmu2009s -1 ) and very high ( ≈ 1000-2000u2009kmu2009s -1 ) velocities. The corresponding structure of the hot object consists of an optically thick, slowly-expanding disk-like material encompassing the accretor at the orbital plane and a fast optically thin wind over the remainder of the star. The disk-like shell persisted around the central star until 2002xa0August as was indicated by the eclipse effect. Then, a significant dilution of the optically thick material and evolution of a fast wind from the hot star, concentrated more at the orbital plane, were detected. A striking similarity of [

AG Draconis observed with XMM-Newton

ion{Fe}{vii}

Discovery of collimated ejection from the symbiotic binary BF Cygni

]u2009 λ 6087 and Ramanxa0 λ 6825 profiles at/after the dilution of the disk suggests their origin within the interaction zone where the winds from the binary components collide.

Electron optical depths and temperatures of symbiotic nebulae from Thomson scattering

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 ,λ 1038 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.

Formation of a disk structure in the symbiotic binary AX Per during its 2007-10 precursor-type activity ⋆

We determine the temporal evolution of the luminosity L(WD), radius R(WD) and effective temperature Teff 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. These aims were achieved by modelling the optical/near-IR spectral energy distribution (SED) using low-resolution spectroscopy (3500 - 9200 A), UBVRcIc and JHKLM photometry. During the fireball stage (Aug. 14.8 - 19.9, 2013), Teff was in the range of 6000 - 12000 K, R(WD) was expanding non-uniformly in time from around 66 to around 300 (d/3 kpc) R(Sun), and L(WD) was super-Eddington, but not constant. After the fireball stage, a large emission measure of 1.0-2.0E+62 (d/3 kpc)**2 cm**(-3) constrained the lower limit of L(WD) to be well above the super-Eddington value. The evolution of the H-alpha line and mainly the transient emergence of the Raman-scattered O VI 1032 A line suggested a biconical ionization structure of the ejecta with a disk-like H I region persisting around the WD until its total ionization, around day 40. 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 during and after the fireball stage represent interesting new challenges for the theoretical modelling of the nova phenomenon.

Measuring the orbital inclination of Z Andromedae from Rayleigh scattering

Context. AG Draconis is the brightest symbiotic star in X-rays and one of the prototypes of the supersoft X-ray source class. Aims. Study of the X-ray spectrum of this peculiar binary system, covering both quiescence and activity periods, is necessary to investigate the physics of the high temperature spectral component, and to unveil the origin of the outbursts. Methods. X-ray and UV observations with XMM-Newton during 2003–2005 and coordinated optical spectrophotometric monitoring, together with archive data, are employed to derive the behaviour of the high energy source of the AG Dra system during different orbital and activity phases. Results. During quiescence the X-ray emission is very soft and is close in strength to the previous ROSAT observations, with an

What Powers the 2006 Outburst of the Symbiotic Star BF Cygni

Context. Detection of collimated ejection from white dwarfs (WD) in symbiotic binaries is very rare and has employed a variety of methods in X-ray, radio, optical imagery, and spectroscopy. To date, its signature in the optical spectra has only been recorded for four objects (MWC 560, Hen 3-1341, StHα 190, and Z And). Aims. We present the first observational evidence of highly-collimated bipolar ejection from the symbiotic binary BF Cyg, which developed during its current (2006-12) active phase, and determine their physical parameters. Methods. We monitored the outburst with the optical high-resolution spectroscopy and multicolour UBVRCIC photometry. Results. During 2009, three years after the 2006-eruption of BF Cyg, satellite components to Hα and Hβ lines emerged in the spectrum. During 2012, they became stable and were located symmetrically with respect to the main emission core of the line. Spectral properties of these components suggest bipolar ejection collimated within an opening angle of <15 ◦ , whose radiation is produced by an optically thin medium with the emission measure of 1−2 × 10 59 (d/3.8 kpc) 2 cm −3 . Conclusions. Formation of the collimated ejection a few years after the eruption and its evolution on a time scale of years at a constant optical brightness can aid us in better understanding the accretion process during the active phases of symbiotic stars.