1. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Bulgarian Academy of Sciences Space Research and Technology Institute Astrophysics and Space Dynamics Department BULGARIAN ACADEMY OF SCIENCES SPACE RESEARCH AND TECHNOLOGY INSTITUTE Acad. G. Bonchev Str., Bl. 1, 1113 Sofia, Bulgaria; tеl./fax:: +359 2 988 35 03; е-mail: office@space.bas.bg, http://www.space.bas.bg

2. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Research topics Dynamics and Evolution of accretion discs Synergetic Physics of Shocks in Astrophysical objects

3. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Dynamics and evolution of accretion disc Credit for animations: Dana Berry, NASA http://www.nasa.gov/centers/goddard/news/ topstory/2003/0702pulsarspeed.html

4. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Magneto-hydrodynamics Hydrodynamics Synergetic Observational Methods and mechanisms of research

5. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Dynamics and evolution of accretion disc Methods and mechanisms of research Results of magneto-hydrodynamical approximation   It is investigated the basic equations of magneto-hydrodynamics for non-stationary and non-axisymmetrical accretion flows.   We developed a new model of MHDs of the accretion disk based on specific advective hypothesis.   It is obtained global solutions for the 2D and 3D structures and the evolution of accretion disk.

6. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Results of magneto-hydrodynamical approximation

7. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Results of magneto-hydrodynamical approximation Two images show the local behavior of the radial velocity (left) and of the magnetic field (right) in the flow. In the results of the disc’s 2D-structure, short-live formation-rings with enhanced density appear. We build the local model of such a formation.

8. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Processed complete all results for key moments t = 1P and t ≈ 0 indicates that the disk develops spherical radiative (non- convective) corona. We analyze the influence of the structure on stream in the primary component, the hot advection accretion disk, over the adaptation in the equations on the secondary component – corona. Results of magneto-hydrodynamical approximation

9. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Dynamics and evolution of accretion disc Methods and mechanisms of research Hydrodynamical approximation  Gas-dynamical numerical calculations: Finite- difference scheme – high order; Roe solver. Box- framed scheme.  Doppler Tomography: To construct the true cart of image of the obtained data; to derive the radiation intensity distribution in the system’s velocity space, making it possible to determine the parameters of the main flow elements in which energy is released.  Polarimetry methods.

10. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © The figure presents the 2D simulation of vorticity time evolution in the accretion flow. The picture visualizes a single vortex formation, which is a part of pattern configuration frame in the final stage of its evolution The 3D view (behavior) of the same “vortex”. The “vortex”- like formation is presented as a patch in the calculating mesh grid. Fig.2 Fig.1 Hydrodynamical approximation: Results: 2D vs. 3D Dynamics and evolution of accretion disc

11. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © relation between structure transformation and flare-ups Stream trajectory from L 1 elliptical disc’s shape tidal waves accretor hot line Stream trajectory from L 1 elliptical disc’s shape tidal waves accretor hot line Simulations of vortical-like wave patterns show they may propagate throughout the disc, along the outer sides. The flow structure during the outburst. A result from the Doppler tomogram with superposed flow elements inferred from the numerical simulations. Hydrodynamical and Observational study Dynamics and evolution of accretion disc Thickened zone formation (the light blue spot, inside of the calculation area), as a result of disturbances in the stability state, caused by mass transfer in a binary system.

12. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Dynamics and evolution of accretion disc Observational study outbursts in Cataclysmic Variables could reveal some disturbances in the mass transfer through the accretion disc. Light curve of CV GK Per (Perseus). GK Per is a CV star, DN or classical novae: a compact white dwarf star and expanded cool giant star in a close orbit. The image is created on the observational data of AAVSO /www.aavso.org/. Light curves of SS Cyg. The vertical lines indicate the dates of our observing nights.

13. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Synergetics 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 system’s 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

14. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Applying of bifurcation analysis 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. The bifurcation theory is a powerful tool for analyzing the nonlinear evolution of instability behavior in pattern forming systems. Synergetics Subjects and methods of research

15. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © a broad variety of objects: 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. Physics of Shocks in Astrophysical objects Research Projects and results

16. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © 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).

17. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Colliding stellar winds in massive binaries Physics of Shocks in Astrophysical objects Research Projects and results  WR+O 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) 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).

18. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © 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.

19. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Project “Аccretion” – Nonlinear dynamics of accretion flows in binary star systems”. International scientific project between SRTI - BAS and Institute of Astronomy of the Russian Academy of Sciences (2006-2015). Project “Аccretion” – Nonlinear dynamics of accretion flows in binary star systems”. International scientific project between SRTI - BAS and Institute of Astronomy of the Russian Academy of Sciences (2006-2015). Projects Based on these results there are many publications and two theses are supported in the past three years.

20. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Projects  COST action MP 1104: Polarisation as a tool to study the Solar System and beyond  ERC Starting Grant 2014: Instability processes in stellar systems with compact objects. Theoretical and observational investigations. Submitted to Horizon 2020

21. Astrophysics and Space Dynamics © Astrophysics and Space Dynamics © Thank you!