Disentangling the composite continuum of symbiotic binaries

Abstract

Abstract. We describe a method of disentangling the composite, 0.12-5 µm continuum of symbiotic binaries. The observed SED is determined by the IUE/HST archival spectra and flux-points corresponding to the optical UBVRI and infrared JHKLM photometric measurements. The modeled SED is given by superposition of fluxes from the cool giant, hot stellar source and nebula including the effect of the Rayleigh scattering process and considering influence of the iron curtain absorptions. We applied this method to 21 S-type symbiotic stars during quiescence, activity and eclipses. We isolated four main components of radiation and determined their properties. (i) Stellar radiation from the giant corresponds to a unique luminosity classnormal giants. Characteristic luminosities are 1600 ± 200 and 290 ± 30 L for red and yellow giants, respectively in our sample of objects. (ii) Hot object radiation during quiescence consists of the nebular and stellar component. The former radiates at a mean electron temperature of 19 000 K and its amount of emission suggests a mass-loss rate from giants via the wind aṫ M W = a few × 10 −7 M yr −1 . Radiation of the latter conforms well with that of a black-body photosphere at a characteristic temperature of 105 000 K. The corresponding effective radii are a factor of ∼10 larger than those of white dwarfs, which thus precludes observing the accretor's surface. Extreme cases of AX Per and V443 Her, for which the hot star temperature from the fit is not capable of producing the nebular emission, signal a disk-like structure of the hot stellar source even during quiescence. (iii) Hot object radiation during activity consists of three components -the stellar and the low-and high-temperature nebular radiation. The stellar radiation satisfies that of a black-body photosphere at a low characteristic temperature of ∼22 000 K (we call it the 1st type of outbursts) or at a very high characteristic temperature of ≈165 000 K (2nd type of outbursts). All the active objects with a high orbital inclination show features of the 1st-type of outbursts (here Z And, AE Ara, CD − 43• 14304, TX CVn, BF Cyg, CH Cyg, CI Cyg, AR Pav, AX Per), while AG Dra represents the 2nd-type. The presence of a two-temperature type of UV spectrum and an enlargement of effective radii of the stellar source by a factor of ∼10 with respect to the quiescent values during the 1st-type of outburst suggest an expansion of an optically thick medium at the orbital plane in the form of a disk. The low-temperature nebula radiates at a mean electron temperature of 14 000 K and is subject to eclipses, while the high-temperature nebula, which is seen during eclipses as the only component, is characterized by T e > 30 000 K. Radiative and geometric properties of the main sources of radiation allowed us to reconstruct a basic structure of the hot object during the 1st-type of outburst. There is an edge-on disk around the accretor. Its outer flared rim represents a warm pseudophotosphere of the hot stellar source, whose radiation is Rayleigh atten...

Ionization structure of hot components in symbiotic binaries during active phases

“…They interpreted these characteristics in terms of the ejection of an optically thick shell, which substantially blocks the UV radiation. Finally, modelling the UV SED of active symbiotic binaries with a high orbital inclination confirmed the presence of such a two-temperature spectrum, where the cool component is produced by a relatively warm stellar source radiating at ≈20 000 K and the hot one is represented by a strong nebular radiation (Skopal 2005). The former is not capable of producing the observed nebular emission, and thus the latter signals the presence of a hot ionizing source ( > ∼ 10 5 K) in the system, which is not seen directly by the observer.…”

“…1) and a large amount of the neutral hydrogen near to the orbital plane of the binary. Column densities derived from the ultraviolet spectra are between ∼10 21 and a few ×10 23 cm −2 (Skopal 2005). A large amount of the neutral material can be identified even around the orbital phase ∼0.5, when the hot component is in front of the cool giant.…”

“…6). For a canonical value of H/R d ≡ 0.3 during active phases Table 4 of Skopal (2005) and Table 8 of Skopal et al (2011).…”

“…Nevertheless, the measured values of n H can still contain a contribution from the giant's wind, which is in the neutral form at/around the orbital plane during active phases, because the ionizing photons are blocked by the neutral disk-like formation surrounding the hot star. For the mass loss rate from the giant of a few ×10 −7 M yr −1 (Skopal 2005), the column density of its wind in the direction to the hot component at the orbital phase 0.5 and i = 90 • is of ≈1 × 10 22 cm −2 (Sekeráš & Skopal 2012b). In spite of large errors in n H and R d , often derived from nonsimultaneous observations, Fig.…”

“…Modelling the SED of symbiotic binaries during active phases showed that the emission measure of the nebular component of radiation is between a few ×10 58 and a few ×10 60 cm −3 (see Table 4 of Skopal 2005). In addition, the modelling revealed the presence of a low-temperature nebula (LTN, T e ∼ 14 000 K), which is subject to eclipses, and a high-temperature nebula (HTN, T e > 30 000 K), which is seen during eclipses as the only component.…”