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

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

The applicability of the wind compression model

Compression of the stellar winds from rapidly rotating hot stars is described by the wind compression model. However, it was also shown that rapid rotation leads to rotational distortion of the stellar surface, resulting in the appearance of non-radial forces acting against the wind compression. In this note we justify the wind compression model for moderately rotating white dwarfs and slowly rotating giants. The former could be conducive to understanding density/ionization structure of the mass outflow from symbiotic stars and novae, while the latter can represent an effective mass-transfer mode in the wide interacting binaries.Comment: 3 pages, A&

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

Ionization structure of hot components in symbiotic binaries during active phases

During active phases of symbiotic binaries, an optically thick medium in the form of a flared disk develops around their hot stars. During quiescent phases, this structure is not evident. We propose the formation of a flared neutral disk-like structure around the rotating white dwarf (WD) in symbiotic binaries. We applied the wind compression model and calculated the ionization boundaries in the compressed wind from the WD using the equation of photoionization equilibrium. During active phases, the compression of the enhanced wind from the rotating WD can form a neutral disk-like zone at the equatorial plane, while the remainder of the sphere above/below the disk is ionized. Calculated hydrogen column density throughout the neutral zone and the emission measure of the ionized fraction of the wind are consistent with those derived from observations. During quiescent phases, the neutral disk-like structure cannot be created because of insufficient mass loss rate. Formation of the neutral disk-like zone at the equatorial plane is connected with the enhanced wind from the rotating WD, observed during active phases of symbiotic binaries. This probably represents a common origin of warm pseudophotospheres, indicated in the spectrum of active symbiotic binaries with a high orbital inclination.Comment: 10 pages, 6 figures, accepted for publication in Astronomy and Astrophysic