Pravidelné semináře pořádáme jednou měsíčně (říjen–červen, zpravidla první pondělí v měsíci) od 13 hod v seminární místnosti pracoviště Ondřejov. (archiv seminářů)
04. 06. 2012
Transition from regular to chaotic motion in black hole magnetospheres
Abstract: We study an astrophysical model consisting of the rotating black hole
immersed into the asymptotically uniform magnetic field. Structure of the
electromagnetic field emerging in the generalized setup involving the
oblique background field (misaligned with the rotation axis) and
translational motion of the black hole is explored in detail. For a
sufficiently rapid drift we localise separator null points of both
electric and magnetic fields. The latter are of an utmost interest since
they prove that the interplay of the rotation and the drift of the compact
body may act as a trigger for magnetic reconnection. Subsequently we study
the motion of charged particles in the simplified setup of aligned field.
We concern ourselves mainly with the dynamic properties of the
trajectories bound in the off-equatorial potential lobes which are
relevant for a description of diluted astrophysical coronae. Employing the
recurrence analysis we locate transitions between regular and chaotic
regimes of motion. Besides the bound off-equatorial orbits we also study
trajectories escaping from the equatorial plane in the collimated jet-like
structures.
( seminární místnost za 2-metrem)
Dále pořádáme menší semináře jednotlivých oddělení:
Semináře slunečního oddělení
Každé úterý v 13:00 (září–červen, s výjimkou úterků po celoústavním semináři) v zasedací místnosti slunečního oddělení pracoviště Ondřejov.
27/06/2012, 13:00Cambridge University UKStudies of Active Regions with Hinode/EIS
Zářivě-(magneto)hydrodynamické semináře
Zpravidla 1x za 14 dní ve čtvrtek od 11 hod (říjen–červen) v zasedací místnosti slunečního oddělení pracoviště Ondřejov.
01/12/2011, 11:00Konkoly Observatory, Budapest, HungaryThe extreme outburst of the young eruptive star EX Lupi in 2008Abstract: EX Lupi is the prototype of EXors, a spectacular group of low-mass pre-main sequence stars characterized by repetitive optical outbursts of 1-5 mag lasting for a few months-to-few years. The outburst is attributed to enhanced accretion from the inner circumstellar disk (within ^X0.1AU) to the stellar surface, probably triggered by an instability in the disk. The historically largest outburst of EX Lupi in 2008 Jan-Sep offered a unique opportunity to understand deeper the physics of the EXor eruptions. In my talk I will summarize the main results of our coordinated observing campaign, in which we used a large set of telescopes to observe and characterize the path of accretion from the disk onto the stellar surface, with the aim of comparing the different models of outburst physics. Our measurements also demonstrated that the brief episodes of highly increased accretion, apart from contributing to the build-up of the final stellar mass, have substantial effect on the structure and composition of the circumstellar material: We discovered episodic crystallization of silicate grains in the disk surface due to the increased luminosity during the 2008 outburst, resulting in material that forms the building blocks of comets and planets.
Semináře oddělení GPS
Zpravidla v knihovně pracoviště Praha–Spořilov v různé dny.
27. 08. 2012, 14:00International School for Advanced Studies, Trieste, ItalyKinetic theory for astrophysical plasmasAbstract: In this talk I will present an overview of the work done during my PhD, which concerns the theoretical foundations of kinetic theory for astrophysical plasmas that can be found in accretion discs around compact objects and in relativistic jets.
First, I will discuss the formulation of kinetic theory for non-relativistic accretion disc plasmas, with particular reference to collisionless axisymmetric magnetized and gravitationally-bound plasmas. I will show how exact quasi-stationary kinetic solutions (equilibria) of the Vlasov equation can be constructed which permit the treatment of quasi-stationary plasmas characterized by non-uniform fluid fields, including temperature and pressure anisotropies, azimuthal and poloidal flows and differential rotation. The significance of these solutions and the implications concerning the self-generation of stationary magnetic fields (kinetic dynamo) in accretion discs will be pointed out.
Second, I will present a solution of the so-called electromagnetic (EM) radiation-reaction (RR) problem characterizing the dynamics of finite-size classical relativistic charged particles. The derivation is based on a variational formulation of the EM RR effect. I will show that, from the Hamiltonian representation of the non-local EM RR effect, a canonical formulation of the kinetic theory for relativistic collisionless plasmas subject to RR can be obtained. This also permits the derivation of the corresponding relativistic fluid equations in which the non-local EM RR contribution can be proved to act as a non-conservative collisional operator. The physical properties of the solution and its astrophysical applications will be discussed.(Takes place at: Sporilov library)