Issue |
A&A
Volume 440, Number 3, September IV 2005
|
|
---|---|---|
Page(s) | 995 - 1031 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20034262 | |
Published online | 05 September 2005 |
Disentangling the composite continuum of symbiotic binaries
I. S-type systems
Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranská Lomnica, Slovakia e-mail: skopal@ta3.sk
Received:
2
September
2003
Accepted:
17
May
2005
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
and infrared
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 1600 ± 200 and 290 ±
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
= a few
10-7
. 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 ~
K (we call it the 1st type of outbursts) or at a very high characteristic temperature of ≈
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,
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
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.
Key words: methods: data analysis / stars: binaries: symbiotic / stars: fundamental parameters / ultraviolet: stars / accretion, accretion disks
© ESO, 2005
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