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

Recent photometry of symbiotic stars - XII

We present new photometric observations of 15 symbiotic stars (EG And, Z And, AE Ara, BF Cyg, CH Cyg, CI Cyg, V1329 Cyg, TX CVn, AG Dra, Draco C-1, RW Hya, SY Mus, AR Pav, AG Peg, AX Per) covering their last orbital cycle(s) from 2003.9 to 2007.2. We obtained our data by both classical photoelectric and CCD photometry. Main results are: EG And brightened by about 0.3 mag in U from 2003. A 0.5 mag deep primary minimum developed in the U light curve (LC) at the end of 2006. Z And continues its recent activity that began during the 2000 autumn. A new small outburst started in summer of 2004 with the peak U-magnitude of about 9.2. During the spring of 2006 the star entered a massive outburst. It reached its historical maximum at U = 8.0 in 2006 July. AE Ara erupted in 2006 February with Dm(vis) approx. 1.2 mag. BF Cyg entered a new active stage in 2006 August. A brightness maximum (U approx. 9.4) was measured during 2006 September. CH Cyg persists in a quiescent phase. During 2006 June - December about 2 mag decline in all colours was measured. CI Cyg started a new active phase during 2006 May - June. After 31 years it erupted by about 2 mag in U. TX CVn maintains a bright stage with U approx. 10.5 from 2003. AG Dra entered a new major outburst in 2006 June. It reached its maximum at U = 8.0 in 2006 September. AR Pav persists at a low level of the activity. AG Peg's LC profile varies markedly during different orbital cycles. AX Per continues its quiescent phase.Comment: 4 pages text, 12 figures, 18 tables, accepted for publication in Astron. Nachrichte

Multiwavelength modelling the SED of supersoft X-ray sources. I. The method and examples

Radiation of supersoft X-ray sources (SSS) dominates both the supersof X-ray and the far-UV domain. A fraction of their radiation can be reprocessed into the thermal nebular emission, seen in the spectrum from the near-UV to longer wavelengths. In the case of symbiotic X-ray binaries (SyXBs) a strong contribution from their cool giants is indicated in the optical/near-IR. In this paper I introduce a method of multiwavelength modelling the spectral energy distribution (SED) of SSSs from the supersoft X-rays to the near-IR with the aim to determine the physical parameters of their composite spectra. The method is demonstrated on two extragalactic SSSs, the SyXB RX J0059.1-7505 (LIN 358) in the Small Magellanic Cloud (SMC), RX J0439.8-6809 in the Large Magellanic Cloud (LMC) and two Galactic SSSs, the classical nova RX J2030.5+5237 (V1974 Cyg) during its supersoft phase and the classical symbiotic star RX J1601.6+6648 (AG Dra) during its quiescent phase. The multiwavelength approach overcomes the problem of the mutual dependence between the temperature, luminosity and amount of absorption, which appears when only the X-ray data are fitted.Thus, the method provides an unambiguous solution. It was found that selection of the model (a blackbody or an atmospheric model) is not of crucial importance in fitting the global X-ray/IR SED. The multiwavelength modelling of the SED of SSSs is essential in determining their physical parameters.Comment: 15 pages, 11 figures, 2 tables, accepted for New Astronom

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

Correction of UBV photometry for emission lines

We investigated the effect on the U, B, V magnitudes of the removal of the emission lines from the spectra of some symbiotic stars and novae during their nebular phases. We approached this problem by a precise reconstruction of the composite UV/optical continuum and the line spectrum. Corrections DU, DB, DV are determined from the ratio of fluxes with and without emission lines. Here we demonstrate this effect on the case of the symbiotic nova V1016 Cyg during its nebular phase. We find that about 68, 78 and 66 per-cent of the observed flux in the U, B and V filters is radiated in the emission lines. The effect should be taken into account before using the observed color indices of emission-line objects for diagnosis of their radiation in the continumm.Comment: 6 pages, 3 Figure