21 research outputs found
Interpretation of the line spectrum of classical symbiotic stars in the scenario for their prototype Z And
Results of the study of the symbiotic binary Z And during its recent active
phase 2000 -- 2010 when it experienced a series of six optical outbursts are
presented. High-resolution spectra obtained during the first and fourth
outburst, which was the strongest one, have been analyzed. These data are
compared with results of theoretical computations. The comparison provides
information about the behaviour of the system during the entire active phase
rather than during an individual outburst. In particular it was found
fundamental difference between the first outburst, which opened the active
phase, and the recurrent outbursts - namely, the presence of bipolar collimated
optical outflow during some of the recurrent outbursts. A scenario that can
explain all the spectroscopic phenomena observed during this active phase as
well as previous active phases of Z And is proposed. The possibility to use
this scenario for explanation of the line spectrum of other classical symbiotic
stars during their active phases is motivated.Comment: 10 pages, 10 figures; to be published in AIP Conf. Proc., School and
Workshop on SPACE PLASMA PHYSICS, Kiten, Bulgaria; corrected typo
A Study of an Outburst in the Classical Symbiotic Star Z And in a Colliding-Wind Model
Two-dimensional gas-dynamical modeling of the mass-flow structure is used to
study the outburst development in the classical symbiotic star Z And. The
stage-by-stage rise of the light during the outburst can be explained in the
framework of the colliding winds model. We suggest a scenario for the
development of the outburst and study the possible influence of the changes of
the flow structure on the light of the system. The model variations of the
luminosity due to the formation of a system of shocks are in good agreement
with the observed light variations
3D Gasdynamic Modelling of the Changes in the Flow Structure During Transition From Quiescent to Active State in Symbiotic Stars
The results of 3D modelling of the flow structure in the classical symbiotic
system Z~Andromedae are presented. Outbursts in systems of this type occur when
the accretion rate exceeds the upper limit of the steady burning range.
Therefore, in order to realize the transition from a quiescent to an active
state it is necessary to find a mechanism able to sufficiently increase the
accretion rate on a time scale typical to the duration of outburst development.
Our calculations have confirmed the transition mechanism from quiescence to
outburst in classic symbiotic systems suggested earlier on the basis of 2D
calculations (Bisikalo et al, 2002). The analysis of our results have shown
that for wind velocity of 20 km/s an accretion disc forms in the system. The
accretion rate for the solution with the disc is ~22.5-25% of the mass loss
rate of the donor, that is, ~4.5-5*10^(-8)Msun/yr for Z And. This value is in
agreement with the steady burning range for white dwarf masses typically
accepted for this system. When the wind velocity increases from 20 to 30 km/s
the accretion disc is destroyed and the matter of the disc falls onto the
accretor's surface. This process is followed by an approximately twofold
accretion rate jump. The resulting accretion rate growth is sufficient for
passing the upper limit of the steady burning range, thereby bringing the
system into an active state. The time during which the accretion rate is above
the steady burning value is in a very good agreement with observations.
The analysis of the results presented here allows us to conclude that small
variations in the donor's wind velocity can lead to the transition from the
disc accretion to the wind accretion and, as a consequence, to the transition
from quiescent to active state in classic symbiotic stars.Comment: 21 pages, 7 figure
On the Astron UV Space Mission Data
The Soviet UV space mission Astron, launched in 1983, had been operational for eight years as the largest ultraviolet space telescope during its lifetime. Astron provided a lot of observational material for various types of astrophysical objects, but unfortunately these data were not widely available and, as a result, unduly forgotten. Here we present some results of our comparison of the Astron data to the modern UV stellar data, such as the NGSL spectral library, discuss the precision and accuracy achieved with Astron, and make some conclusions on potential application areas of these data
On the Construction of a New 3D Atlas of Stellar Spectral Energy Distributions
Modern spectrophotometric atlases are burdened with significant systematic errors. In particular, the problems of spectrum calibration in the ultraviolet region are not solved; different parts of the spectrum are not thoroughly fit to each other; spectra of (even bright) stars, obtained by different authors, display large discrepancies. Here we discuss a possibility to construct a new atlas of spectral energy distributions (SEDs) for a large set of stars by comparison of empirical stellar spectra in dozens of modern spectrophotometric atlases, as well as the comparison of synthetic and observed color indices in different multicolor photometric systems. In this way we suppose to exclude most of systematic errors and construct a new three-dimensional (spectral class, luminosity class, metallicity) atlas of empirical stellar spectra for several thousand stars. After exclusion of interstellar reddenings, a semi-empirical atlas of average SEDs can be constructed for about 150â200 spectral subtypes. This would allow us to make calibrations of spectrophotometric and photometric parameters in terms of spectral types and physical parameters (Teff, log g, [m/H]) and to verify the accuracy of model stellar atmospheres