astrophysics and space dynamics © astrophysics and space dynamics © bulgarian academy of sciences...

Astrophysics and Space Dynamics Astrophysics and Space Dynamics ©©

Bulgarian Academy of Sciences Space Research and Technology

Institute

Astrophysics and Space Dynamics Astrophysics and Space Dynamics DepartmentDepartment

BULGARIAN ACADEMY OF SCIENCESSPACE RESEARCH AND TECHNOLOGY INSTITUTEAcad. G. Bonchev Str., Bl. 1, 1113 Sofia, Bulgaria; tеl./fax:: +359 2 988 35 03; е-mail: [email protected], http://www.space.bas.bg


Research topicsResearch topics

Dynamics and Evolution of accretion discs

Synergetic

Physics of Shocks in Astrophysical objects


Dynamics and evolution of accretion disc

Credit for animations: Dana Berry, NASAhttp://www.nasa.gov/centers/goddard/news/topstory/2003/0702pulsarspeed.html


Magneto-hydrodynamics

Hydrodynamics

Synergetic

Observational

Methods and mechanisms of research


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-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.


The distribution of dimensionless function of the equatorial density f1(X,Y) in non-axisymmetric MHD model.

Profiles (x;Z) in 3D for densities contours f1(x, Z) = 106; 108; 1010. at the moment t=1P~Ω0

-1.

The distribution of dimensionless function of the equatorial density f1(X,Y) at the moment t≈0.

Profiles (x;Z) in 3D for densities contours f1(x, Z) = 106; 108; 1010. at the moment t≈0.

7e+07 7.5e+07 8e+07 8.5e+07 9e+07 9.5e+07

0 x 1

0

Z

0.08

1010

108

106

f1(X,Y)

-1

X 0

-1

0

1 Y

0

1e+09

0 1 x

0

0.08

Z 1010

108

106

-1

0

X

-1

0

1 Y

0

1e+09

f1(X,Y)

The distribution of [f2(x,Z), f9(x,Z)] in the plane (x, Z). This is a vector field of the velocity v(vr,vz) . It shows the trend of plasma drift in z.

Development of condition ||va|<|vs|| in x of level Z ~ const.

(0.075; 0.08) Z.

(0.055; 0.06)Z.

(0.035; 0.04) Z. (0.001; 0.002)Z.

0 1 x 0

1e+10

0 1 x 0

10000

0 1 x 0

1000

0 1 x 0

1000

0

0.08

Z

1 x

),( zr vvv

|va|<|vs|

|va|<|vs| |va|>|vs|

|va|>|vs| |va|<|vs|

|va|>|vs| |va|<|vs|

|va|>|vs|

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.


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.


Vertical boundary distributions of the function of the equatorial density

Cylindrical boundary contours of the function of the equatorial density

0

-1

X 0

1

Y

1

f1H(X,Y) 0 0.2 0.6 1 x 0

f1(x, H)

0

-1

0

1 1

Y X

f1H(X,Y) 0 0.2 0.6 1 x

0

f1(x, H)

1e+05

1e+08


Dynamics and evolution of accretion discMethods 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.


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.

•Hydrodynamical approximation: Results: 2D vs. 3D



• relation between structure transformation and flare-ups

Stream trajectory from L 1elliptical disc ’s

shape

tidal waves

accretor

hot line

Stream trajectory from L 1elliptical disc ’s

shape

tidal waves

accretor

hot line

50z

20

10 y0x

-10

-10

10

30

-20

-20

20

0

-20

pm P.t~ 2500

20 3010

20

x0

-20y

-20 0

-10

-20

10-10

z

50

pm P.t~ 5500

-20

20-10

0

x y

10

-2030

20 -10

010

-20

z

50

pm P.t~ 7500

50z

20

10 y0x

-10

-10

10

30

-20

-20

20

0

-20

pm P.t~ 2500

50z

20

10 y0x

-10

-10

10

30

-20

-20

20

0

-20

pm P.t~ 2500

20 3010

20

x0

-20y

-20 0

-10

-20

10-10

z

50

pm P.t~ 5500 20 3010

20

x0

-20y

-20 0

-10

-20

10-10

z

50

pm P.t~ 5500

-20

20-10

0

x y

10

-2030

20 -10

010

-20

z

50

pm P.t~ 7500

-20

20-10

0

x y

10

-2030

20 -10

010

-20

z

50

pm P.t~ 7500

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


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.



• 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.


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


• 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.

-80-60

-40-20

020

4060

80

lambda(c)

-40-20

020

4060

80100

120

w(c)

-4

-2

0

2

4Psi(r)

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


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



• 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).


• Colliding stellar winds in massive binaries


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).



• 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 theorigin 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 possessmassive and fast winds driven by radiation pressure and subject to instabilities (radiation-driven instabilities) which may give rise to the formation of strong shocks.


Project “Аccretion” – Nonlinear dynamics of accretion flows in binary Project “Аccretion” – Nonlinear dynamics of accretion flows in binary star systems”. International scientific project between SRTI - BAS star systems”. International scientific project between SRTI - BAS and Institute of Astronomy of the Russian Academy of Sciences and Institute of Astronomy of the Russian Academy of Sciences

(2006-2015).(2006-2015).

Projects

Based on these results there are many publications and two Based on these results there are many publications and two theses are supported in the past three years.theses are supported in the past three years.


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


Thank you!Thank you!

astrophysics and space dynamics © astrophysics and space dynamics © bulgarian academy of sciences...

Documents