Astrophysics and Synergetic Department

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SPACE RESEARCH INSTITUTE

• Astrophysics and Synergetic Department

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Research topics

• Dynamics and Evolution of accretion discs
• Nonlinear dynamics and chaos
• Physics of Shocks in Astrophysical objects

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Dynamics and evolution of accretion disc
Credit for animations Dana Berry,
NASA http//www.nasa.gov/centers/goddard/news/tops
tory/2003/0702pulsarspeed.html
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Dynamics and evolution of accretion discMethods
and mechanisms of research

• Results of magneto-hydrodynamical approximation

• It is investigated the basic equations of
  magneto-hydrodynamics for non- stationary and
  non- axissymmetrical accretion flows.? we
  obtain global solutions for the 2D and 3D
  structures and the evolution of accretion disk.
  Here we will illustrating some of our results.

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• Results of magneto-hydrodynamical approximation

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• Results of magneto-hydrodynamical approximation

• In 3D for planes Zconst and x const we can get
  the distribution of level for the chosen
  coordinate.For contours 108 and 1010 on the
  density for t 0 we observe maximums and this
  mark for t 0, spreading is going on.

• The solution in moment t 0O0-1 , in the form
  f1(x)exp(-?0f7(x)/O0) along the all disc, because
  instantly after the spreading of the disk there
  are not instabilites, yet. The coefficient ?(r)
  is indefinitely and the coefficient kf(r) is
  zero.
• We obtain the local dependences of instabilities
  from warming, the dependence of local warming
  from global distributions and entropy in tame and
  along the disk ( feeding up of
  instabilities).
• We discuss results, investigate local condition
  va lt vs, in terms of magneto-rotation instability
  existing on different levels for different radius
  in disk and their connection with generating of
  the corona like consequences.
• We use the potentialities on the developed model
  in two concrete objects, representatives of low
  massive and super-massive BH ? 10?o and ?
  10n?o. Aim to do results comfortably for
  comparative analyses.
• Modifying is the disk model for conditions in
  disks corona. Aim to do possible to put stitches
  the solution for corona with solution in disk,
  when the two global flows have no total
  energetics.

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Results of magneto-hydrodynamical approximation
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Dynamics and evolution of accretion discMethods
and mechanisms of research

• Results of hydrodynamical approximation

• Linear analysis show that the discs
  configuration remain stable.
• In nonlinear study it is needed to apply
  numerical codeRunge-Kutta numerical method,
  combined with computational software, gives the
  next graphical results

Two images show the variations of density /left/
and exceeding of velocity /right/ in the flow.
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Dynamics and evolution of accretion discMethods
and mechanisms of research

• Results of thermodynamic approach

• Considerations of entropy distribution show
  radial entropy gradient decreases to the negative
  values. This is one of the condition for the
  structures formation and baroclinic instability
  in the accretion disc flow.

It is seen the sharp drop of the entropy gradient
in rectangular 3D plot performance
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Dynamics and evolution of accretion discMethods
and mechanisms of research

• Results of thermodynamic approach numerical
  simulation of vortices formation.

• Further development of the baroclinic
  instability turns it into the source of vorticity
  formations in the discs. Applying numerical code,
  and after performing a series of runs, it is
  presented the simulation of this kind of pattern
  growth in plane of the disc zone.

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Dynamics and evolution of accretion discMethods
and mechanisms of research

• Results of thermodynamic approach

• disturbances in instability state of the disc
  flow are expressed as pulsations, bursts, rapidly
  rotation, quasi-periodic oscillations and etc.
  The cataclysmic outbursts occur when the density
  and temperature rises high enough to ignite
  nuclear fusion reactions.

Temperature evolution of the flow in the presence
of white dwarf companion. It is shown the
exchange of temperature value, when the infalling
accreting matter interacts with white dwarf.
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Dynamics and evolution of accretion discMethods
and mechanisms of research

• Observational effects of unstable behavior

• Observationally, the outbursts and pulsations of
  Cataclysmic Variables are expressed in their
  light curves and revealed by exchanges in
  luminosities.

Light curve of CV GK Per /Perseus/ (RK catalogue
of X-ray stars). It is observed the X-Ray
pulsations with rapid than slow irregular
variations in the luminosity. The image is
created on the observational data of AAVSO
/www.aavso.org/.
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Dynamics and evolution of accretion discMethods
and mechanisms of research

• Applying the bifurcation analysis

• The bifurcation theory is a powerful tool for
  analyzing the nonlinear evolution of instability
  behavior in pattern forming systems.

• a bifurcation is any qualitative or topology
  reconstruction of the system, when the parameter
  of the system crosses its critical value. When a
  given system passes through a bifurcation point,
  it may lose its stability. It is seen in the
  figure this transition trough the critical point.

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Non-linear dynamic and chaos Subjects and
methods of research

• Study of the Driving forces- stabilization and
  disruptive modes
• Systems Evolution Hierarchies- their
  Transitional Stages and Time scales
• Time- "periodicity"- paradoxes in the structure
  of an astrophysical systems activity
• The trigger effects from Interstellar dust
  properties, giant planets sudden energy
  release (GRB) influence on IPM, magnetic field
  generation planetary atmospheres
• A Study of Possible Scenarios as a Result of
  Rapid and/or Burst-like, Long-term

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Physics of Shocks in Astrophysical objects
Research Projects and results

• In general, this topic may include a broad
  variety of objects but the basic interests here
  are related to shocks in stellar winds, their
  interaction with the interstellar matter,
  supernova remnants. Since the gas flows in the
  studied objects are highly supersonic, the
  postshock temperatures are of the order of a
  million Kelvin and even much higher, therefore,
  the primary shock emission is in X-rays. All the
  observations that are part of this science
  project are done with the modern X-ray
  observatories Chandra (NASA) and XMM-Newton
  (ESA), as the three basic subprojects are as the
  following.

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Physics of Shocks in Astrophysical objects
Research Projects and results

• Monitoring the birth of the supernova remnant
  in the Large Magelanic Cloud (SNR 1987A)

• A new phenomenological model is being
  developed that is capable of explaining the
  observed X-ray emission and how it is related to
  the shock emission in other spectral domains.

The observations are done as part of numerous
projects with the Chandra X-ray observatory (PI
Prof. D. Burrows, The Pennsylvania State
University, USA for the imaging in 2000 - 2009
PI Prof. R. McCray, University of Colorado at
Boulder, USA for the spectral observations in
2004-2007) The figure is published in S. Zhekov
et al. (2004, Astrophysical Journal, 628,
L127-L130).
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Physics of Shocks in Astrophysical objects
Research Projects and results

• Colliding stellar winds in massive binaries

• WRO binaries are one of the brightest X-ray
  sources amongst the massive stars. Their enhanced
  emission originates from the interaction region
  of the winds of the two massive stars. A
  phenomenon called colliding stellar winds
• (CSW) being an ideal laboratory for studying the
  shock physics.

A new CSW model (see Figure 3) was used to
analyse the X-ray spectrum of the massive binary
system WR 147 that was obtained with the
XMM-Newton X-ray observatory (PI Dr. S. Skinner,
University of Colorado at Boulder, USA). The
figure is from S. Zhekov (2007, MNRAS, 382,
886-894).
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Physics of Shocks in Astrophysical objects
Research Projects and results

• X-ray emission from single massive stars

• It was used for analysis of a sample of 15
  massive OB stars. The data were taken from the
  archive of the Chandra observatory. X-ray spectra
  of presumably single WR stars were analysed over
  the years. These projects are based on data taken
  with Chandra and XMM-Newton X-ray telescopes (PI
  PI Dr. S.Skinner,University of Colorado at
  Boulder, USA).

• The present concept on the
• origin of X-rays in massive stars (OB and
  Wolf-Rayet) posits that they are emitted by hot
  gas heated by shocks. OB and WR stars possess
• massive and fast winds driven by radiation
  pressure and subject to instabilities
  (radiation-driven instabilities) which may give
  rise to the formation of strong shocks.

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Thank you!