19 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
Russian Virtual Observatory: Data Sources
The purpose of this review is to analyze main directions of creation and functioning of major data sources developed by Russian astronomers or with their participation and to compare them with the worldwide trends in these fields. We discuss astronomical space missions of the past, present, and future (Astron, INTEGRAL, WSO-UV, Spectrum Roentgen Gamma, Lyra-B), high-quality photometric atlases and catalogues, and spectroscopic data sources, primarily VALD and the global VAMDC framework for the maintenance and distribution of atomic and molecular data. We describe collection, analysis, and dissemination of astronomical data on minor bodies of the Solar System and on variable stars. Also described is the project joining data for all observational types of binary and multiple stars, Binary star DataBase (BDB)