Discovery of the eclipse in the symbiotic binary Z Andromedae

Our photometric observations of the symbiotic binary Z And during its recent (2000 -- 2003) active phase revealed a minimum in the U, B and V light curves (LC) at the position of the inferior conjunction of its cool component (the orbital phase 'phi' = 0). This fact and the behaviour of colour indices suggest that the minimum was due to the eclipse of the active hot object by the red giant. Physically plausible fit of the eclipse profile and a precise analysis of the spectral energy distribution (SED) in the ultraviolet continuum suggest a disk-like structure for the hot object during active phases. The present knowledge of fundamental parameters of the system limits the orbital inclination 'i' to 76 - 90 deg. The presence of the Rayleigh attenuated far-UV continuum at 'phi' around 0 during quiescent phase confirms the very high inclination of the Z And orbit.Comment: 4 pages, 3 figures, accepted for Astronomy and Astrophysics as a Lette

Multiwavelength modelling the SED of supersoft X-ray sources III. RS Ophiuchi: The supersoft X-ray phase and beyond

I modelled the 14 \AA - 37 $\mu$m SED of the recurrent symbiotic nova RS Oph during its supersoft source (SSS) phase and the following quiescent phase. During the SSS phase, the model SEDs revealed the presence of a strong stellar and nebular component of radiation in the spectrum. The former was emitted by the burning WD at highly super-Eddington rate, while the latter represented a fraction of its radiation reprocessed by the thermal nebula. During the transition phase, both the components were decreasing and during quiescence the SED satisfied radiation produced by a large, optically thick disk (R(disk) > 10 R(Sun)). The mass of the emitting material was (1.6 +/- 0.5) x 1E-4(d/1.6 kpc)**(5/2) M(Sun). The helium ash, deposited on the WD surface during the whole burning period, was around of 8 x 1E-6(d/1.6kpc)**2 M(Sun), which yields an average growing rate of the WD mass, dM(WD)/dt ~ 4 x 1E-7(d/1.6 kpc)**2 M(Sun)/yr. The mass accreted by the WD between outbursts, m(acc) ~ 1.26 x 1E-5 M(Sun), constrains the average accretion rate, dM(acc)/dt ~ 6.3 x 1E-7 M(Sun)/yr. If the wind from the giant is not sufficient to feed the WD at the required rate, the accretion can be realized from the disk-like reservoir of material around the WD. In this case the time between outbursts will extend, with the next explosion beyond 2027. In the opposite case, the wind from the giant has to be focused to the orbital plane to sustain the high accretion rate at a few times 1E-7 M(Sun)/yr. Then the next explosion can occur even prior to 2027.Comment: 14 pages, 6 figures, 2 tables, accepted by New Astron. on May 20, 2014; follow-up of arXiv:1402.612

Measuring the orbital inclination of Z Andromedae from Rayleigh scattering

The orbital inclination of the symbiotic prototype Z And has not been established yet. At present, two very different values are considered, i ~ 44 degrees and i >~ 73 degrees. The correct value of i is a key parameter in, for example, modeling the highly-collimated jets of Z And. The aim of this paper is to measure the orbital inclination of Z And. First, we derive the hydrogen column density (nH), which causes the Rayleigh scattering of the far-UV spectrum at the orbital phase phi = 0.961 plus/minus 0.018. Second, we calculate nH as a function of i and phi for the ionization structure during the quiescent phase. Third, we compare the nH(i,phi) models with the observed value. The most probable shaping of the HI/HII boundaries and the uncertainties in the orbital phase limit i of Z And to 59 -2/+3 degrees. Systematic errors given by using different wind velocity laws can increase i up to ~74 degrees. A high value of i is supported independently by the orbitally related variation in the far-UV continuum and the obscuration of the OI] 1641 A emission line around the inferior conjunction of the giant. The derived value of the inclination of the Z And orbital plane allows treating satellite components of H-alpha and H-beta emission lines as highly-collimated jets.Comment: 6 pages, 7 figures, accepted for Astronomy and Astrophysic

The hydrogen and helium lines of the symbiotic binary Z And during its brightening at the end of 2002

High resolution observations in the region of the lines Halpha, He II 4686 and Hgamma of the spectrum of the symbiotic binary Z And were performed during its small-amplitude brightening at the end of 2002. The profiles of the hydrogen lines were double-peaked. These profiles give a reason to suppose that the lines can be emitted mainly by an optically thin accretion disc. The Halpha line is strongly contaminated by the emission of the envelope, therefore for consideration of accretion disc properties we use the Hgamma line. The Halpha line had broad wings which are supposed to be determined mostly from radiation damping but high velocity stellar wind from the compact object in the system can also contribute to their appearance. The Hgamma line had a broad emission component which is assumed to be emitted mainly from the inner part of the accretion disc. The line He II 4686 had a broad emission component too, but it is supposed to appear in a region of a high velocity stellar wind. The outer radius of the accretion disc can be calculated from the shift between the peaks. Assuming, that the orbit inclination can ranges from 47$^\circ$ to 76$^\circ$, we estimate the outer radius as 20 - 50 R_sun. The behaviour of the observed lines can be considered in the framework of the model proposed for interpretation of the line spectrum during the major 2000 - 2002 brightening of this binary.Comment: 19 pages, 5 figures. Accepted for publication in Astronomy Report

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

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.Comment: 14 pages, 9 figures, 3 tables, accepted for Astronomy and Astrophysic

On the effect of emission lines on the UBVR photometry

We investigate the effect on the U, B, V, Rc and Rj magnitudes of the removal of emission lines from a spectrum. We determined "Dm" corrections from the ratio of fluxes with and without emission lines, transmitted from the object through the photometric filter. An exact and a simplified approach for operative use were applied. The effect was demonstrated for classical symbiotic stars, symbiotic novae and the classical nova V1974 Cyg. It was found that about 20-30, 30-40, 10 and 26/20 percents of the observed flux in the U, B, V and Rc/Rj filter, respectively, is radiated in the emission lines of the investigated classical symbiotic stars. The largest effect was found for symbiotic novae (RR Tel and V1016 Cyg) and the classical nova V1974 Cyg at 210 days (in average of 74, 79, 56 and 66/60 percents). Examples for practical application are suggested.Comment: 8 pages, 6 figures, 2 tables, New Astron. in pres

Formation of a disk-structure and jets in the symbiotic prototype Z And during its 2006-2010 active phase

We present an analysis of spectrophotometric observations of the latest cycle of activity of the symbiotic binary Z And from 2006 to 2010. We estimate the temperature of the hot component of Z And to be \approx 150000 - 170000 K at minimum brightness, decreasing to \approx 90000 K at the brightness maximum. Our estimate of the electron density in the gaseous nebula is N_{e}=10^{10}-10^{12} cm^{-3} in the region of formation of lines of neutral helium and 10^6-10^7 cm^{-3} in the region of formation of the [OIII] and [NeIII] nebular lines. A trend for the gas density derived from helium lines to increase and the gas density derived from [OIII] and [NeIII] lines to simultaneously decrease with increasing brightness of the system was observed. Our estimates show that the ratios of the theoretical and observed fluxes in the [OIII] and [NeIII] lines agree best when the O/Ne ratio is similar to its value for planetary nebulae. The model spectral energy distribution showed that, in addition to a cool component and gaseous nebula, a relatively cool pseudophotosphere (5250-11 500 K) is present in the system. The simultaneous presence of a relatively cool pseudophotosphere and high-ionization spectral lines is probably related to a disk-like structure of the pseudophotosphere. The pseudophotosphere formed very rapidly, over several weeks, during a period of increasing brightness of Z And. We infer that in 2009, as in 2006, the activity of the system was accompanied by a collimated bipolar ejection of matter. In contrast to the situation in 2006, the jets were detected even before the system reached its maximum brightness. Moreover, components with velocities close to 1200 km/s disappeared at the maximum, while those with velocities close to 1800 km/s appeared.Comment: 18 pages, 19 figures, Accepted for publication in Astronomy Report