We describe a method of disentangling the composite , 0.12 – 5 \mu m 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 class – normal giants .
Characteristic luminosities are 1 600 \pm 200 and 290 \pm 30 L _ { \sun } 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 at \dot { M } _ { W } = a few \times 10 ^ { -7 } M _ { \sun } { 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 \sim 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 \sim 22 000 K ( we call it the 1st type of outbursts ) or at a very high characteristic temperature of \approx 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 ^ { \circ } 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 \sim 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 attenuated and affected by the iron curtain absorptions in the neutral gas concentrated at the orbital plane .
The low-temperature nebula is placed just above/below the disk with a concentration at its edge as to be subject to eclipses and to ’ see ’ well the central ionizing source .
High above/below the orbital plane , there is a hot nebular emitting region .